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VHF-21( )/22( ) VHF Comm Transceiver



instruction book (repair manual)



23-12-10



NOTICE INFORMATION SUBJECT TO EXPORT CONTROL LAWS This document contains technical data that may be restricted for export under the International Traffic in Arms Regulations (ITAR) or the Export Administration Regulations (EAR). Violations of these export laws may be subject to fines and penalties under the Arms Export Control Act (22 U.S. C. 2778).



© Copyright 2001, Rockwell Collins, Inc. All rights reserved.



Rockwell Collins, Inc. #523-0771854



Jul 30, 2002



TO:



HOLDERS OF THE COLLINS® VHF-21( )/22( ) VHF COMM TRANSCEIVER INSTRUCTION BOOK (REPAIR MANUAL) (523-0771854) NINTH EDITION, THIRD REVISION, HIGHLIGHTS



The attached change pages replace pages in the existing manual. All changes have been implemented in a manner that retains information required to service earlier equipment models. Black bars in the margin of the page identify all revisions. The purpose of the revision was to implement SB 42, add test select part numbers, and add alternate parts numbers. • • • • •



Cover letter Title page Record of Revisions Schematics and Illustrated Parts Lists Title Page (2 sheets) Schematics and Illustrated Parts Lists pages 6-1, 6-2, 6-3, 6-4, 6-9, 6-10, 6-27, 6-28, 6-133, 6-134, 6-135, 6-136, 6-145, 6-146, 6-147, 6-148, 6-153, 6-154, 6-157, 6-158, 6-159, 6-160, 6-169, 6-170, 6-171, 6-172, 6-177, 6-178, 6-181, 6-182, 6-183, 6-184 TECHNICAL OPERATIONS



VHF-21( )/22( ) VHF Comm Transceiver



instruction book (repair manual) This publication includes: Theory of Operation Maintenance Schematics and Illustrated Parts Lists Bulletins Appendix



523-0771858 523-0771859 523-0771860 523-0771861 523-0771889



Pro Line II Comm/Nav/Pulse System Installation Manual (CPN 523-0772719) contains installation, operation, and on-aircraft fault isolation information for the VHF-21( )/22( ).



Notice Specialized sophisticated test equipment and extensive depot level repair training are required for testing the equipment covered in this manual. Therefore, this manual may not be used to test or repair the subject equipment unless the using facility has been specifically authorized by Rockwell Collins, Inc. to do so. This manual does not need to be kept current if it is only used for reference purposes.



Printed in the United States of America © Copyright 2001, Rockwell Collins, Inc. All rights reserved.



Rockwell Collins, Inc. Cedar Rapids, Iowa 52498 523-0771854-30911A



|secJONLOO|f_Loj|griv|PMLMO|



23-12-10



9th Edition, 1 October 2001 3rd Revision, 30 July 2002 T-1



ROCKWELL COLLINS INSTRUCTION BOOK (REPAIR MANUAL) VHF-21( )/22( ) VHF COMM TRANSCEIVER EXPORT CONTROL LAWS This document contains technical data that may be restricted for export under the International Traffic in Arms Regulations (ITAR) or the Export Administration Regulations (EAR). Violations of these export laws may be subject to fines and penalties under the Arms Export Control Act (22 U.S. C. 2778). PROPRIETARY NOTICE NOTICE: FREEDOM OF INFORMATION ACT (5 USC 552) AND DISCLOSURE OF CONFIDENTIAL INFORMATION GENERALLY (18 USC 1905) This document and the information disclosed herein are proprietary data of Rockwell Collins, Inc. Neither this document nor the information contained herein shall be used, reproduced, or disclosed to others without the written authorization of Rockwell Collins, Inc., except to the extent required for installation or maintenance of recipient’s equipment. This document is being furnished in confidence by Rockwell Collins, Inc. The information disclosed herein falls within exemption (b) (4) of 5 USC 552 and the prohibitions of 18 USC 1905.



SOFTWARE COPYRIGHT NOTICE © COPYRIGHT 2001 - 2002 ROCKWELL COLLINS, INC. ALL RIGHTS RESERVED. All software resident in this equipment is protected by copyright. We welcome your comments concerning this manual. Although every effort has been made to keep it free of errors, some may occur. When reporting a specific problem, please describe it briefly and include the manual part number, the paragraph or figure number, and the page number. Send your comments to: Rockwell Collins, Inc. Collins Aviation Services 350 Collins Road NE, M/S 153-250 Cedar Rapids, IA 52498-0001 Email: [email protected] All requests for product orders or inquires please contact. Send your request to:



Email:



Rockwell Collins, Inc. Customer Response Center 400 Collins Road NE, M/S 133-100 Cedar Rapids, IA 52498-0001 TELEPHONE: 1.888.265.5467 INTERNATIONAL: 1.319.265.5467 FAX: 319.295.4941 [email protected]



23-12-10



T-2 Apr 1/02



VHF-21( )/22( ) instruction book 523-0771854



RECORD OF REVISIONS REV NO



ISSUE DATE



DATE INSERTED



BY



REV NO



ISSUE DATE



DATE INSERTED



BY



Instruction book revision dates prior to the 8th edition are unavailable. 8th Ed



11 Sep 98



9th Ed



1 Oct 01



9th Ed, 1st Rev



1 Apr 02



9th Ed, 2nd Rev



24 May 02



9th Ed, 3rd Rev



30 Jul 02



RR-1/RR-2 30 Jul 2002



23-12-10



ROCKWELL COLLINS INSTRUCTION BOOK (REPAIR MANUAL) VHF-21( )/22( ) VHF Comm Transceiver RECORD OF TEMPORARY REVISIONS TEMPORARY REV NO



PAGE NUMBER



1



5-48



Nov 19/02 Rockwell Collins



1



6-279



Nov 19/02 Rockwell Collins



1



6-280



Nov 19/02 Rockwell Collins



1



6-283



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1



6-295



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6-296



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6-299



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5-34



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6-7



Dec 5/02 Rockwell Collins Sep 15/03 Rockwell Collins



3



6-335



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4-2



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4-3



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Rockwell Collins



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6-32



Oct 9/03



Rockwell Collins



7



6-6



7



6-429



Temporary Revision 14 523-0771854-3E911A



DATE ISSUED



BY



DATE REMOVED



BY



Apr 27/04



Rockwell Collins



Apr 27/04 Rockwell Collins



Mar 6/07



Rockwell Collins



Apr 27/04 Rockwell Collins



Aug 3/04



Rockwell Collins



23-12-10



RTR-1 Mar 6/07



ROCKWELL COLLINS INSTRUCTION BOOK (REPAIR MANUAL) VHF-21( )/22( ) VHF Comm Transceiver RECORD OF TEMPORARY REVISIONS TEMPORARY REV NO



PAGE NUMBER



7



6-432



7



DATE ISSUED



DATE REMOVED



BY



Apr 27/04 Rockwell Collins



Mar 6/07



Rockwell Collins



6-437



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Rockwell Collins



7



6-440



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8



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6-431



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6-437



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6-439



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6-441



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9



5-37



Dec 7/04 Rockwell Collins



Jul 19/05



Rockwell Collins



9



5-47



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Rockwell Collins



10



4-19



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6-101



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6-111



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6-116



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5-36



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Rockwell Collins



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11



5-40



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11



5-47



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Sep 8/05 Rockwell Collins



Temporary Revision 14 523-0771854-3E9113



BY



23-12-10



RTR-2 Mar 6/07



ROCKWELL COLLINS INSTRUCTION BOOK VHF-21( )/22( ) VHF Comm Transceiver RECORD OF TEMPORARY REVISIONS TEMPORARY REV NO



PAGE NUMBER



13



5-36



Oct 10/05 Rockwell Collins



13



5-37



Oct 10/05 Rockwell Collins



13



5-40



Oct 10/05 Rockwell Collins



13



5-47



Oct 10/05 Rockwell Collins



14



Maintenance Section List of Effective Pages



Mar 6/07



Rockwell Collins



14



Schematics and Illustrated Parts Lists Section List of Effective Pages



Mar 6/07



Rockwell Collins



14



6-7



Mar 6/07



Rockwell Collins



14



6-432



Mar 6/07



Rockwell Collins



14



6-440



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15



6-216



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6-225



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6-236



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15



6-237



Sep 17/07 Rockwell Collins



DATE ISSUED



BY



DATE REMOVED



BY



Export Control Classification Notice (ECCN) for this document is 7E994.



Temporary Revision 15 523-0771854-3F911A



23-12-10



RTR-3/RTR-4 Sep 17/07



GENERAL ADVISORIES FOR ALL UNITS



Warning Service personnel are to obey standard safety precautions, such as wearing safety glasses, to prevent personal injury while installing or doing maintenance on this unit. Warning Use care when using sealants, solvents and other chemical compounds. Do not expose to excessive heat or open flame. Use only with adequate ventilation. Avoid prolonged breathing of vapors and avoid prolonged contact with skin. Observe all cautions and warnings given by the manufacturer. Warning Remove all power to the unit before disassembling it. Disassembling the unit with power connected is dangerous to life and may cause voltage transients that can damage the unit. Warning This unit may have components that contain materials (such as beryllium oxide, acids, lithium, radioactive material, mercury, etc) that can be hazardous to your health. If the component enclosure is broken, handle the component in accordance with OSHA requirements 29CFR 1910.1000 or superseding documents to prevent personal contact with or inhalation of hazardous materials. Since it is virtually impossible to determine which components do or do not contain such hazardous materials, do not open or disassemble components for any reason. Warning This unit exhibits a high degree of functional reliability. Nevertheless, users must know that it is not practical to monitor for all conceivable system failures and, however unlikely, it is possible that erroneous operation could occur without a fault indication. The pilot has the responsibility to find such an occurrence by means of cross-checks with redundant or correlated data available in the cockpit. Caution Turn off power before disconnecting any unit from wiring. Disconnecting the unit without turning power off may cause voltage transients that can damage the unit. Caution This unit contains electrostatic discharge sensitive (ESDS) components and ESDS assemblies that can be damaged by static voltages. Although most ESDS components contain internal protection circuits, good procedures dictate careful handling of all ESDS components and ESDS assemblies.



Obey the precautions given below when moving, touching, or repairing all ESDS components and units containing ESDS components. a. Deenergize or remove all power, signal sources, and loads used with the unit. b. Place the unit on a work surface that can conduct electricity (is grounded). c. Ground the repair operator through a conductive wrist strap or other device using a 470-kΩ or 1-MΩ series resistor to prevent operator injury.



i



GENERAL ADVISORIES FOR ALL UNITS (CONT)



d. Ground any tools (and soldering equipment) that will contact the unit. Contact with the operator's hand is a sufficient ground for hand tools that are electrically isolated. e. All ESDS replacement components are shipped in conductive foam or tubes and must be stored in their shipping containers until installed. f. ESDS devices and assemblies that are removed from a unit must immediately be put on the conductive work surface or in conductive containers. g. Place repaired or disconnected circuit cards in aluminum foil or in plastic bags that have a layer of, or are made with, conductive material. h. Do not touch ESDS devices/assemblies or remove them from their containers until they are needed. Failure to handle ESDS devices as described above can permanently damage them. This damage can cause immediate or premature device failure.



ii



n523-0771858-109118 8th Edition, 1 Oct 2001 1st Revision, 24 May 2002



VHF-21( )/22( ) VHF Comm Transceiver Theory of Operation Table of Contents Paragraph



Page



4.1 INTRODUCTION ................................................ 4-1 4.2 PURPOSE OF EQUIPMENT.............................. 4-1 4.3 EQUIPMENT SPECIFICATIONS ..................... 4-2 4.4 OVERVIEW .......................................................... 4-6 4.5 VHF-21/22 (A/B) FUNCTIONAL THEORY OF OPERATION....................................................... 4-7 4.5.1 Interface Circuits .................................................. 4-7 4.5.2 Control Circuits..................................................... 4-7 4.5.3 Frequency Synthesizer ......................................... 4-7 4.5.4 Receiver ................................................................. 4-7 4.5.5 Automatic Squelch Circuits.................................. 4-9 4.5.6 Receiver Audio Circuit.......................................... 4-9 4.5.7 Transmitter ........................................................... 4-9 4.5.8 Modulator Circuit ................................................. 4-9 4.5.9 Power Supply Circuits .......................................... 4-9 4.6 VHF-21/22 (A/B) DETAILED THEORY OF OPERATION....................................................... 4-9 4.6.1 Interface Circuits .................................................. 4-9 4.6.2 Control Circuits................................................... 4-12 4.6.3 Frequency Synthesizer ....................................... 4-14 4.6.4 Receiver Circuit................................................... 4-16 4.6.5 Automatic Squelch Circuits................................ 4-18 4.6.5.1 Noise Squelch Circuit ...................................... 4-18 4.6.5.2 Carrier Squelch Circuit ................................... 4-18 4.6.6 Receiver Audio Circuits ...................................... 4-19 4.6.7 Transmitter Circuit ............................................ 4-20



NOTICE: This title page replaces eighth edition, dated 1 October 2001



Paragraph



Page



4.6.8 Modulator Circuit................................................ 4-21 4.6.9 Power Supply Circuits ........................................ 4-23 4.6.10 Filter Assembly Circuits................................... 4-24 4.7 VHF-21/22 (C/D) FUNCTIONAL THEORY OF OPERATION..................................................... 4-24 4.7.1 Interface Circuits ................................................ 4-24 4.7.2 Control Circuits................................................... 4-24 4.7.3 Frequency Synthesizer ....................................... 4-26 4.7.4 VCO Assembly..................................................... 4-26 4.7.5 Receiver ............................................................... 4-26 4.7.6 Automatic Squelch Circuits................................ 4-26 4.7.7 Transmitter ......................................................... 4-27 4.7.8 Modulator Circuit................................................ 4-27 4.7.9 Power Supply Circuits ........................................ 4-27 4.8 VHF-21/22 (C/D) DETAILED THEORY OF OPERATION..................................................... 4-27 4.8.1 Interface Circuits ................................................ 4-27 4.8.2 Control Circuits................................................... 4-29 4.8.3 Frequency Synthesizer Circuit........................... 4-31 4.8.4 VCO Circuit ......................................................... 4-34 4.8.5 Receiver Circuit................................................... 4-35 4.8.6 Noise Squelch Circuits........................................ 4-37 4.8.7 Receiver Audio Circuit ........................................ 4-38 4.8.8 Transmitter Circuit............................................. 4-38 4.8.9 Modulator Circuit................................................ 4-39 4.8.10 Power Supply Circuits ...................................... 4-40 4.8.11 Filter Assembly Circuits................................... 4-42



List of Effective Pages Page No



*The asterisk indicates pages changed, added, or deleted by the current change.



Issue



* Title ......................................... 24 May 02 * List of Effective Pages............. 24 May 02 4-1 thru 4-20 ............................... 1 Oct 01 * 4-21 thru 4-23 .......................... 24 May 02 4-24 thru 4-42 ............................. 1 Oct 01



RETAIN THIS RECORD IN THE FRONT OF THE MANUAL. ON RECEIPT OF REVISIONS, INSERT REVISED PAGES IN THE MANUAL, AND ENTER DATE INSERTED AND INITIALS.



Record of Revisions REV NO



REVISION DATE



INSERTION DATE/BY



SB NUMBER INCLUDED



1st Ed



10 Jun 83



1



2nd Ed



2 Jan 85



1 thru 8



3rd Ed



13 Apr 87



9 thru 13



4th Ed



19 Jul 90



14 thru 20



5th Ed



1 Apr 92



21



6th Ed



11 Aug 93



20R3, 21R1



7th Ed



11 Sep 98



22, 23R1, 24R1, 25, 26, 27



8th Ed



1 Oct 01



28R1, 29, 30R1, 31, 32R1, 33R1, 34R1, 35 thru 41



1st Rev



24 May 02



REV NO



REVISION DATE



INSERTION DATE/BY



SB NUMBER INCLUDED



section



IV



theory of operation 4.1 INTRODUCTION This repair manual provides all the specifications, principles of operation, and information necessary to test, troubleshoot, and repair the VHF-21( ) and VHF-22( ) VHF Comm Transceivers. Refer to Table 4-1 for a list of equipment covered. Refer to the Pro Line II Comm/Nav/Pulse System Installation Manual (Collins part number 523-0772719) for installation, operation, and on-aircraft fault isolation information. The VHF-22A is shown in Figure 4-1. 4.2 PURPOSE OF EQUIPME NT The VHF-21( )/22( ) transceivers are remote-mounted, multichannel vhf voice transceivers providing AM voice communications in the frequency range from 118.000 through 135.975, 136.975, 136.992, or 151.975 Mhz. The VHF-21/22(A/B) transceivers provide channel spacing in 25-kHz increments. The VHF21/22(C/D) transceivers provide channel spacing in either 8.33- or 25-kHz increments. The major difference between the VHF-21( ) and VHF-22( ) is the type of electrical connector. The VHF-21( ) is intended for direct replacement of a VHF-20( ), while the VHF-22( ) is intended for new installations. The A, B, C, or D suffix on the equipment type number shows the frequency range of that transceiver as indicated in Table 4-1. On the VHF-21/22(A/B), the last three digits of the equipment part number define the bandwidth of the receiver circuits. Units with -0X1 part numbers have a narrow bandwidth and are intended for operation in areas using 25-kHz channel spacing with or without offset carriers. Units with -0X2 part numbers have a wider bandwidth and will operate satisfactorily in areas where the received carrier frequency varies as much as 13 kHz from nominal. All VHF-21/22(C/D) units have a narrow bandwidth. Units with -X2X and -X3X part numbers are compatible with RTCA/DO-160D, section 21, category H emissions in the GPS band (1.575 GHz).



Figure 4-1. VHF-22A VHF Comm Transceiver



Revised 1 October 2001



4-1



theory of operation 523-0771858 Table 4-1. Equipment Covered. CONNECTOR EQUIPMENT



COLLINS PART NUMBER



DPA



THINLINE II



FREQ RANGE (MHZ) 118.000 TO 135.975



118.000 TO 136.975*



118.000 TO 151.975



VHF-21A



622-6389-001



X



X



VHF-21A



622-6389-002



X



X



VHF-21A



622-6389-011



X



X



VHF-21A



622-6389-012



X



X



VHF-21B



622-6390-001



X



X



VHF-21B



622-6390-002



X



X



VHF-21C



822-1111-001



X



VHF-21D



822-1112-001



X



VHF-22A



622-6152-001



X



X



VHF-22A



622-6152-002



X



X



VHF-22A



622-6152-011



X



X



VHF-22A



622-6152-012



X



X



VHF-22A†



622-6152-021



X



X



VHF-22A†



622-6152-022



X



X X



SELECTIVITY NARROW



WIDE



X X X X



X



X X X



X



X X X X X X X



VHF-22A#



622-6152-023



X



VHF-22A†



622-6152-031



X



X



X



VHF-22A†



622-6152-032



X



X



VHF-22A#



622-6152-033



X



X



VHF-22B



622-6153-001



X



VHF-22B



622-6153-002



X



VHF-22B†



622-6153-021



X



VHF-22B†



622-6153-022



X



VHF-22B#



622-6153-023



X



VHF-22C



822-1113-001



X



X



X



VHF-22C†



822-1113-021



X



X



X



X X X X



X



X X



X X



X X



X



X



VHF-22D



822-1114-001



X



X



X



VHF-22D†



822-1114-021



X



X



X



* On VHF-21/22(C) units, frequency range extends to 136.992 MHz. † GPS system compatible. # Reduced low-frequency transmitter input audio response.



4.3 EQUIPMENT SPECIFIC ATIONS Refer to Table 4-2 for equipment specifications. Table 4-2. VHF-21( )/22( ) VHF Comm Transceiver Equipment Specifications. CHARACTERISTIC



SPECIFICATION



Certification FAA TSO



Revised 1 October 2001



-C37c, C38c



4-2



ROCKWELL COLLINS INSTRUCTION BOOK (REPAIR MANUAL) VHF-21( )/22( ), VHF COMM TRANSCEIVER VHF-21( )/22( ) VHF Comm Transceiver INSTRUCTION BOOK (REPAIR MANUAL) (523-0771854, 3RD REVISION, DATED JUL 30/02)



TEMPORARY REVISION NO. 23-12-10-05 Insert facing page 4-2, 23-12-10. Subject: Additional equipment covered. The equipment listed below is added to Table 4-1. Table 4-1. Equipment Covered. CONNECTOR EQUIPMENT



COLLINS PART NUMBER



DPA



FREQ RANGE (MHZ)



THINLINE II



VHF-22C†#



822-1113-023



X



VHF-22D†#



822-1114-023



X



118.000 TO 135.975



118.000 TO 136.975*



118.000 TO 151.975



X



SELECTIVITY NARROW



WIDE



X X



X



* On VHF-21/22(C) units, frequency range extends to 136.992 MHz. † GPS system compatible. # Reduced low-frequency transmitter input audio response.



Temporary Revision 5 523-0771854-35911A



23-12-10



Page 1 of 5 Sep 15/03



ROCKWELL COLLINS INSTRUCTION BOOK (REPAIR MANUAL) VHF-21( )/22( ), VHF COMM TRANSCEIVER VHF-21( )/22( ) VHF Comm Transceiver INSTRUCTION BOOK (REPAIR MANUAL) (523-0771854, 3RD REVISION, DATED JUL 30/02)



TEMPORARY REVISION NO. 23-12-10-05 Insert facing page 4-3, 23-12-10. Subject: Revised equipment weight. Change to VHF-21( )/22( ) nominal weight is shown below in bold text. Table 4-2. VHF-21( )/22( ) VHF Comm Transceiver Equipment Specifications. CHARACTERISTIC Weight



Temporary Revision 5 523-0771854-35911A



SPECIFICATION 2.22 kg (4.9 lb) nominal



23-12-10



Page 2 Sep 15/03



theory of operation 523-0771858 Table 4-2. VHF-21( )/22( ) VHF Comm Transceiver Equipment Specifications. CHARACTERISTIC



SPECIFICATION



EUROCAE



ED-23, ED-24



FCC



Part 15, Part 87 (modulation designator 6A3, 13A9); VHF-21/22(D) is not approved by FCC



Environmental



RTCA document DO-160A, categories /A2E1/B/JY/EXXXXXZ/BZ/AZA; EUROCAE ED-14A



Physical Size



3/8-ATR, short, dwarf



Height



85.3 mm (3.36 in) max



Width



95.3 mm (3.75 in) max



Length



355.6 mm (14.0 in) max



Weight



2.12 kg (4.7 lb) nominal



Mounting



Remote mounted in UMT-12 (preferred) or 390R-19 mount (alternate). (Refer to the VHF21( )/22( ) installation section for details.)



Unit connector



VHF-21( ) — Cannon pn DPA-29W1-34P (CPN 370-2224-020); coax insert: Cannon pn 2495052-000 (CPN 370-2461-010) VHF-22( ) — CPN 634-2699-003 (Thinline II connector); coax insert: CPN 372-2519-210



Mating connector



VHF-21( ) — Cannon pn DPA-29W1-33S-1 (CPN 370-2225-010); coax insert: Cannon pn DPA-50048-2 (CPN 370-2182-000) VHF-22( ) — CPN 653-1286-001 Thinline II, 52/2 pin connector; coax insert: CPN 372-2519040 for RG-58, CPN 372-2519-100 for RG-400



Environmental Temperature range Operational



–55 to +70 °C (–67 to +158 °F)



Storage



–55 to +85 °C (–67 to +185 °F)



Altitude



21300 m (70000 ft) maximum



Cooling



Convection



Relative humidity



95% at +65 °C (+149 °F) for 10 days



Shock Operational



6g



Crash safety



15 g (10-ms duration)



Vibration



Certified for use in piston or turbine, fixed or rotary wing aircraft 0.2 in da, 5.0 to 14 Hz; 2 g, 14 to 44 Hz; 0.02 in da, 44 to 54 Hz; 3 g, 54 to 2000 Hz



Maintenance requirement



On condition.



Electrical Power requirements (VHF-21( ) P1-1; VHF-22( ) P1-49, 50)



Receive — 0.5 A (14 W) at 27.5 V dc Transmit — 6.0 A (165 W) at 27.5 V dc



Power-on relay (VHF-22( ) P1-37, 38)



1.3 W (46 mA at 27.5 V dc). +28 V dc applied to pin P1-37 and ground on P1-38 energizes an internal relay which applies power to the unit from the +28- V dc input, P1-49, 50.



Frequency range VHF-21A/22A



118.000 to 135.975 MHz, VHF-21A/22A: -001 and -002 units; VHF-22A: -021, -022, -023 units 118.000 to 136.975 MHz, VHF-21A/22A:- 011 and -012 units; VHF-22A: -031, -032, -033 units



VHF-21B/22B



118.000 to 151.975 MHz, all VHF-21B units and VHF-22B: -001, -021 and -023 units 118.000 to 136.975 MHz, VHF-22B: -002, -022 units



VHF-21C/22C



118.000 to 136.992 MHz



VHF-21D/22D



118.000 to 151.975 MHz



Revised 1 October 2001



4-3



theory of operation 523-0771858 Table 4-2. VHF-21( )/22( ) VHF Comm Transceiver Equipment Specifications. CHARACTERISTIC



SPECIFICATION



Frequency stability VHF-21/22(A/B)



±0.0015%



VHF-21/22(C/D)



±0.0005%



Frequency control



CSDB or ARINC 2-out-of-5



CSDB inputs (VHF-21( ) P1-23, 25; VHF-22( ) P1-40, 39)



Two-wire CSDB data bus provides a balanced differential signal using nominally 0- to 5-V switching levels from the connected CTL-22/22A/22C.



CSDB outputs (VHF-21( ) P1-16, 11; VHF-22( ) P1-44, 43)



Two-wire CSDB data bus provides a balanced differential signal using nominally 0- to 5-V switching levels to the connected CTL-22/22A/22C.



2-out-of-5



Grounds (0.0 ±1.0 V dc) two inputs out of five for each, open (greater than 100 kΩ) the remaining three lines. Refer to ARINC 410 2-out-of-5.



Serial/parallel select (VHF-21( ) P1-9, 10, 24; VHF-22( ) P1-32)



Strapped = serial (CSDB) selected (VHF-21( ) connect P1-9, 10, and 24 to P1-3; VHF-22( ) connect P1-32 to P1-31); open = parallel (2-out-of-5) selected



Unit ident (VHF-21( ) P1-20, 19; VHF-22( ) P1-28, 27)



Defines the unit as comm 1, comm 2, or comm 3 as follows (open = greater than 100 kΩ; ground = 0.0 ±1.0 V dc): COMM 1



COMM 2



COMM 3



Unit ident A



Open



Ground



Open



Unit ident B



Open



Open



Ground



Channels VHF-21A/22A



720, 25-kHz increments (extendible to 760)



VHF-21B/22B



1360, 25-kHz increments



VHF-21C/22C



8.33- kHz increments from 118.000 through 136.992 MHz. 25-kHz increments only when operated on 2-out-of-5 tuning.



VHF-21D/22D



8.33- kHz increments from 118.000 through 136.992 MHz, 25-kHz increments from 137.000 through 151.975 MHz. 25-kHz increments only when operated on 2-out-of-5 tuning.



Transmitter Output power



16 W minimum into a 52-Ω resistive load; emergency low voltage with 18-V dc input power operation; output power 6 W minimum



Modulation



85% modulation capability with less than 15% distortion; 95% limiting



Mic audio input impedance (VHF-21( ) P1-7; VHF-22( ) P1-13)



150 Ω unbalanced with excitation current for a 50- to 600-Ω transistorized dynamic or transistorized electret microphone. Carbon microphones can be used but are not recommended due to their poor audio quality.



Duty cycle VHF-21/22(A/B)



1 minute transmit, 4 minutes receive



VHF-21/22(C/D)



30 second transmit, 4.5 minutes receive



Sidetone (VHF-21( ) P1-27, 6; VHF-22( ) P1-26, 25)



100 mW into a 600-Ω load



Receiver Sensitivity



Revised 1 October 2001



3 µV for 6-dB (s+n)/n



4-4



theory of operation 523-0771858 Table 4-2. VHF-21( )/22( ) VHF Comm Transceiver Equipment Specifications. CHARACTERISTIC



SPECIFICATION



Selectivity VHF-21/22(A/B) -0X1 part number (narrowband statuses)



Typical 6 dB at ±8 kHz, 60 dB at ±17 kHz



-0X2 part number (wideband statuses)



Typical 6 dB at ±15 kHz, 60 dB at ±35 kHz



VHF-21/22(C/D)



For channels between 118.000 and 136.992 MHz, selected as 1XX.000, 1XX.025, 1XX.050, and 1XX.075 and all channels between 137.000 MHz and 151.975 MHz for “D” units: 6 dB: 60 dB:



±8 kHz minimum ±20 kHz maximum



For all other channels: 6 dB: 60 dB:



±2.78 kHz minimum ±7.37 kHz maximum



Spurious response VHF-21/22(A/B)



10-mV spurious signal produces no more output than a desired signal producing 6 dB (s+n)/n.



VHF-21/22(C/D)



Attenuated at least 80 dB relative to the desired response at or beyond the second adjacent channel. Responses at either adjacent channel are attenuated at least 60 dB relative to the desired response.



Squelch



Automatic (phase noise reduction) with carrier override



AGC characteristics



3 dB maximum variation from 5 µV to 1 V



Emergency low-voltage power operation



Receiver meets all specifications at 18-V input power.



Audio (VHF-21( ) P1-26, 6; VHF-22( ) P1-18, 17)



100 mW into a 600-Ω load; frequency range, within 6 dB from 350 to 2500 Hz; down 18 dB minimum at 4000 Hz



Combined audio (VHF-21( ) P1-5, 6; VHF-22( ) P1-30, 29)



Audio output is switched to sidetone when in transmit (switched with relay contacts), receive audio normally (not in transmit).



SELCALä output (VHF-21( ) P1-28; VHF-22( ) P1-34, 33)



0.5 V rms across a 600-Ω load



Receiver compression disable (VHF-21( ) internal strap; VHF-22( ) P1-9)



Ground (0.0 ±1.0 V dc) on VHF-22( ) P1-9 = receiver audio compressor disabled; open = receiver audio compressor enabled. The VHF-21( ) has the receiver audio compressor disabled; refer to the VHF-21( )/22( ) repair manual for additional information.



Squelch disable (VHF-21( ) P1-4; VHF-22( ) P1-36)



Ground (0.0 to ±1.0 V dc) = squelch disabled; open (greater than 100 kΩ) = squelch normal



Simulcomm (VHF-22( ) P1-21)



Ground from opposite side comm keyline reduces the receiver gain to reduce interference when transmitting.



Noise squelch test (For test only) (VHF-22( ) P1-6)



Carrier squelch test (For test only) (VHF-22( ) P1-5)



AGC test (For test only) (VHF-21( ) P1-21) (VHF-22( ) P1-10)



Revised 1 October 2001



Used for monitoring noise squelch state. Ground = audio output disabled (squelched); noise level at the noise squelch detector is above the preset threshold. +12 V dc = audio output enabled; noise level at the noise squelch detector is below the preset threshold. Used for monitoring carrier squelch state. Ground = audio output disabled (squelched); AGC voltage is below the preset threshold of the carrier squelch circuit. +12 V dc = audio output enabled; AGC voltage is above the preset threshold of the carrier squelch circuit. Provides AGC voltage test point to rear connector.



4-5



theory of operation 523-0771858



4.4 OVERVIEW The VHF-21( ) and VHF-22( ) are used with a frequency control unit, an antenna, and the aircraft audio system to provide two-way vhf voice communications. The VHF-21( ) is intended for direct replacement of a VHF-20( ), while the VHF-22( ) is intended for new installations. The transceivers accept either 2-out-of-5 parallel or RS-422A serial-digital tuning data from a frequency control unit. Figure 4-2 illustrates four typical system configurations, which are described below. a. The retrofit configuration shows the VHF-21( ) replacing a VHF-20( ) in an existing installation with a parallel tune control unit. b. The VHF-21( ) serial control configuration shows the VHF-21( ) with a serial frequency control unit and an external power control relay. c. The VHF-22( ) parallel control configuration shows the VHF-22( ) with a parallel frequency control unit. d. The VHF-22( ) serial control configuration shows the VHF-22( ) with a serial frequency control unit.



Figure 4-2. Typical VHF Comm System Configurations



Revised 1 October 2001



4-6



theory of operation 523-0771858 4.5 VHF-21/22(A/B) FUNCTI ONAL THEORY OF OPERATION (REFER TO FIGURE 4-3) 4.5.1 Interface Circuits All input and output signals to the comm transceivers are applied through the rear connector and interface circuits on circuit card assembly (CCA) A1. Two different A1 assemblies are used; one has a DPA rear connector and is used with the VHF-21( ), and the other has a Collins Thinline connector and is used with the VHF-22( ). The interface circuits on both A1 assemblies provide noise filtering, transient protection, serial output data buffering, and parallel-to-serial input data conversion. 4.5.2 Control Circuits Overall control of the comm transceiver is provided by a single 8-bit microprocessor located on control/synthesizer circuit card A4. All pilot initiated commands entered via the associated panel-mounted comm control and the mic button are connected through the interface circuits on A1 to the microprocessor. The microprocessor interprets these commands to determine the operating mode and frequency of the transceiver. The microprocessor also monitors selected parameters within the transceiver to ensure that each is within a predetermined range. If an out-of-limit condition is detected, the microprocessor sends an audible alert (two beeps at 800 Hz) to the audio system, and may interrupt a transmission if a critical fault is detected during the transmit mode. 4.5.3 Frequency Synthesizer The frequency synthesizer is a large-scale integrated (LSI) circuit, digital frequency synthesizer that phase locks a voltage-controlled oscillator (vco) to a single 6.4-MHz crystal oscillator. The crystal oscillator determines the overall frequency stability of the synthesizer. The synthesizer provides the 118.000- to 151.975MHz excitation for the transmitter RF amplifiers and the 118.000- to 131.950-MHz low-side and 138.025- to 158.025-MHz high-side injection signals for the first mixer circuit in the receiver. All synthesizer frequencies are selectable in 25-kHz increments. The vco tune voltage within the synthesizer is also processed and used to tune the varactors in the 4-stage receiver preselector. 4.5.4 Receiver The receiver is a dual-conversion superheterodyne type with IF frequencies of 25.025 MHz and 455 kHz. Frequency conversion is performed by two mixer circuits. The first is a dual JFET mixer with either highside or low-side injection from the synthesizer, and the second is a dual-gate MOSFET mixer with injection from a 19.57-MHz local oscillator. Four varactor-tuned preselector filters provide RF selectivity. The IF selectivity is determined by two 20.025-MHz crystal filters. The IF filters used in some transceivers have a narrower bandwidth than those used in wide bandwidth transceivers. Refer to Table 4-1 for a listing of these transceivers. This minimizes adjacent channel interference in systems using 25-kHz channel spacing. A 455-kHz IF amplifier IC provides approximately 80 dB of IF gain prior to detection. The audio signal from the detector is applied to the receiver AGC circuits, the automatic squelch circuit, and the audio output amplifiers. Multiple AGC circuits hold the receiver output constant over a wide range of RF signal levels. Filter assembly A8 reduces FM interference caused by high-power FM radio stations.



Revised 1 October 2001



4-7



theory of operation 523-0771858



Figure 4-3. VHF-21/22 (A/B) VHF Comm Transceiver, Block Diagram



Revised 1 October 2001



4-8



theory of operation 523-0771858 4.5.5 Automatic Squelch Circu its Two automatic squelch circuits are used in the transceiver: carrier squelch and noise squelch. The carrier squelch is derived from the receiver AGC voltage and is used to open the squelch when multiple carriers are received. The noise squelch circuit uses a multifunction FM IF IC to detect phase noise rather than amplitude noise. This feature provides reliable automatic squelch operation with minimal degradation due to ignition noise or receiver gain variations. 4.5.6 Receiver Audio Circuit The receiver audio circuit provides three audio outputs: receiver audio, transmit sidetone, and receiver audio with transmit sidetone. An audio compressor reduces loudness variations when receiving signals with different modulation depths. An independent SELCALä amplifier provides unsquelched, low-power audio for connection to a selective calling decoder or direction-finding equipment. 4.5.7 Transmitter The transmitter is a broadband solid-state circuit excited by the synthesizer output. Minimum unmodulated output power is 16 watts over the frequency range from 118.000 to 151.975 MHz. One class-A stage and three class-C stages provide the necessary amplification. The output of the modulator is applied to the two final stages to provide 85 to 95 percent modulation. A low-pass filter following the final stage suppresses harmonic energy. 4.5.8 Modulator Circuit The modulator circuit consists of an audio compressor and a class-D power amplifier that is similar to a power supply switching regulator. The audio compressor ensures that proper modulation depth is maintained with different microphone signal levels. A 107-kHz triangle waveform chops the compressor output signal to generate the pulse width modulated drive for the class-D amplifier. A low-pass filter after the amplifier suppresses the switching signal and its harmonics, but passes the modulated dc component for the RF power amplifiers in the transmitter. 4.5.9 Power Supply Circuits The power supply circuits, on CCA A3, consist of an LC filter, an overvoltage protection circuit, two +12-V dc regulators, a +5-V dc regulator, and a +16-V dc switching regulator. These circuits provide power to all of the circuits in the transceiver except the synthesizer IC and the tune-voltage amplifier, which have separate +5V dc and +23-V dc regulators, respectively, on control/synthesizer circuit card A4. 4.6 VHF-21/22 (A/B) DETAIL ED THEORY OF OPERATION 4.6.1 Interface Circuits (Refer to Figure 4-4 and Figure 6-10 thru Figure 6-13) All input and output signals to the transceiver are applied through the rear connector and interface circuits on circuit card A1. Different interface circuit cards are used in the VHF-21( ) and VHF-22( ) due to the different rear connectors. The major differences between the two circuit cards are the power relay provided only in the VHF-22( ) and the serial/parallel select logic. Both of these differences are caused by the smaller number of pins available in the rear connector on the VHF-21( ).



Revised 1 October 2001



4-9



theory of operation 523-0771858



Figure 4-4. VHF-21/22( ) Interface Circuits, Block Diagram



The power relay in the VHF-22( ) is controlled by a low-current input from the comm control. Both terminals of the relay coil are available at the unit connector so that the transceiver power can be controlled by either a switched +28-V dc signal or a switched ground signal. In the VHF-22( ), the serial/parallel select logic consists of a single rear connector pin (P101-32) that is connected through an RC filter and the parallel-to-serial converter to the microprocessor. Grounding the serial/parallel select pin on the VHF-22( ) causes the microprocessor to take frequency data from the serial tuning control. When this pin is open, the frequency data is taken from the parallel (2-out-of-5) control. Both types of controls can be connected to the transceiver simultaneously, with the state of the serial/parallel select pin determining the tuning source. The serial data output in the VHF-22( ) is always active and provides active frequency and diagnostic information back to the serial tuning control, even when the frequency is determined by the parallel control. Also, when both type controls are connected, the transceiver responds to squelch control from either control and responds to the self-test command from the serial control, even when operating in the parallel mode. Additional serial/parallel select logic is required in the VHF-21( ) because the serial and parallel modes share several of the same rear connector pins and cannot function independently as they can in the VHF22( ). This circuit monitors three of the parallel frequency data lines, and provides a signal to the microprocessor and enables the serial data buffers when the serial mode is selected. The serial data mode is selected when all three of the monitored parallel data lines are grounded simultaneously. This combination of parallel bits would be an invalid 2-out-of-5 code and would never occur legitimately in a parallel-tuned installation. The serial data output buffer is active only when the transceiver is strapped for serial tuning.



Revised 1 October 2001



4-10



theory of operation 523-0771858 The serial data received and transmitted by the VHF-21( )/22( ) conforms to the CSDB (Commercial Standard Digital Bus) format. A non-return-to-zero synchronous transmission is used with one start bit, eight data bits, an odd parity bit, and one stop bit. This group of data is called a byte. A logic 1 is defined as line A positive with respect to line B, and a logic 0 is defined as line B positive with respect to line A. The start bit is always a logic 0 and the stop bit is always a logic 1. The data transmission rate is approximately 12.5 Kbits/second with a refresh rate of approximately 10/second. Data transferred on the comm serial bus is organized in blocks of six bytes. The first block in a transmission must be a sync block consisting of six hexadecimal A5 characters. Each subsequent data block consists of a label byte, a status byte, and four message bytes. The data within each byte is transmitted with the least significant bit first. All parallel frequency data lines and some of the input control lines are filtered by RC filter circuits with pullup resistors connected to +12 V dc. All of these input data lines except the squelch disable and keyline are applied to a parallel/serial converter consisting of two 8-bit shift registers. The data applied to the shift register is periodically latched in the registers by a strobe signal from the microprocessor. The data is then shifted from the registers by clock pulses from the microprocessor. The 17 bits of data available from the parallel-to-serial converter are defined as follows:



BIT



DEFINITION



0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16



1 = parallel tune, 0 = serial tune Unit identification A Unit identification B 10 MHz A 10 MHz B 10 MHz C 1 MHz A 1 MHz B 1 MHz C 1 MHz D 0.1 MHz A 0.1 MHz B 0.1 MHz C 0.1 MHz D 0.01 MHz C 0.01 MHz D Upper frequency limit (VHF-21A/22A only) 0 = 135.975 MHz 0 = 136.975 MHz



Revised 1 October 2001



4-11



theory of operation 523-0771858 The 2-out-of-5 frequency Select Code used for parallel tuning is defined below. FREQ DIGIT 10, 1, 0.1 MHz



2-OUT-OF-5 CODE A B C D



0 1 2 3 4 5 6 7 8 9



1 0 0 1 1 1 1 1 0 0



0 0 1 0 0 1 1 1 1 1



1 1 0 0 1 0 0 1 1 1



1 1 1 1 0 0 1 0 0 1



1 0 0 1



1 1 0 0



kHz 00 25 50 75



All input and output audio signal lines are filtered to suppress noise entering or leaving the transceiver. 4.6.2 Control Circuits (Refer t o Figure 4-5 and Figure 6-31 thru Figure 6-38) The heart of the control circuit is microprocessor U702. The microprocessor (µP) is an 8-bit parallel processor with 2048 bytes of program memory and 128 bytes of data memory on a single MOS chip. The µP monitors the input data lines and internal sensors, generates control signals and data for the synthesizer, and transmits status information to the comm control. The operating frequency of the microprocessor is determined by a 3.2-MHz crystal, Y402, connected to a clock oscillator circuit within the microprocessor. The microprocessor periodically checks the input data lines for frequency tuning data and control signals. The first data checked is the serial/parallel strapping of the transceiver, which determines whether the µP uses the parallel or serial frequency tuning data. This strapping data is the first bit of data available for the µP after strobing parallel data into the parallel-to-serial converter on interface card A1. After receiving frequency tuning data, the µP examines the data to ensure that it is valid and within the operating range of the transceiver. If an invalid frequency is received after operation on a valid frequency, the µP continues to use the last valid frequency for both receive and transmit modes. If an out-of-range frequency is received after operation on a valid frequency, the µP continues to use the last valid frequency for receive mode but inhibits the transmit mode. If an invalid or out-of-range frequency is applied, the µP automatically tunes the transceiver to the 121.500-MHz emergency frequency and permits operation in both the receive and transmit modes. The µP uses the valid frequency data to program the synthesizer to generate the required receiver or transmitter injection frequency. The µP reprograms the synthesizer each time a new frequency is received, each time the key line is closed or opened, and every 120 msec during continuous operation in the receive mode. The data sent to the synthesizer is contained in the 19-bit serial word defined below.



Revised 1 October 2001



4-12



theory of operation 523-0771858 BIT



DEFINITION



1



VHF-21A/22A (don't care) VHF-21B/22B: Logic 0 = 118.000 thru 138.000 MHz Logic 1 = 138.025 thru 151.975 MHz (This bit adjusts for the tune voltage break between high-side and lowside receiver injection.) Don't care N counter MSB



2 3 thru 12 13 thru 19



N counter LSB A counter MSB A counter LSB



The programmed frequency data word is sent to the synthesizer via dedicated data, clock, and latch lines. The 19-bit data word is transferred into the synthesizer shift register one bit at a time by the clock signal (see Figure 4-6). The data word is then transferred to latches that control loading of the A and N counters. The microprocessor initiates the transmit mode when it detects a logic 0 on the key line. This causes the µP to apply a logic 0 to the RF enable line which removes the synthesizer injection to both the receiver and the transmitter. The µP then sends the proper frequency data to the synthesizer to generate the desired transmitter injection frequency and waits for a logic 1 lock detector signal. After the synthesizer is locked, the µP applies a logic 1 to the RF enable and XMIT enable lines and starts a 120-second timer. This applies the RF injection signal to the transmitter and enables operation of the modulator circuit. If the transmit mode is maintained for 120 seconds, the µP returns the transceiver to the receive mode by resetting the RF and XMIT enable lines to logic 0, reprogramming the synthesizer for the receiver injection frequency, then resetting the RF enable line to logic 1. After detecting a logic 1 on the key line (transmit key released), the µP initiates two audio bursts on the receive audio output to indicate that the 120-second transmit limit was exceeded. If the transmit key is released before the 120-second limit, the µP returns the transceiver to the receive mode but does not generate the audio bursts. The µP monitors the transmitter temperature and the synthesizer lock signal during the transmit mode. If the synthesizer is not locked or the temperature sense voltage exceeds 1.60 V dc, the µP returns the transceiver to the receive mode and generates two audio bursts to indicate the failure. The µP will not initiate the transmit mode if the key line is closed while excessive transmitter temperature is being monitored unless the key line is closed, opened, and then closed a second time within 1.5 seconds. This allows emergency transmissions during an overtemperature condition. During normal operation, the µP sends a logic 0 pulse to the heartbeat circuit every 100 milliseconds. Failure of the µP to send this pulse causes the heartbeat circuit to reset the µP. After any reset (including power up), the µP performs a checkerboard test of its internal RAM and starts the 800-Hz audio oscillator. If the test is successfully completed, the µP turns off the audio tone and resumes normal operation. If a failure is detected, the µP locks up in an endless loop that prevents further operation of the transceiver. During normal operation, the µP routinely performs various diagnostic checks to ensure proper operation of the transceiver. Many of these checks involve the measurement and comparison of analog voltages which must be converted to digital data before they can be processed by the µP. This conversion is performed by a/d converter U707 under the control of the µP. Only one analog voltage can be converted at a time. Each conversion is initiated when the µP sets the address of the desired analog on the 3-bit address bus and applies a logic 0 to the ALE input to the converter. The conversion is performed by the successive approximation method and takes at least 64 cycles of the ALE output from the µP to complete. The resulting digital data is



Revised 1 October 2001



4-13



theory of operation 523-0771858



Figure 4-5. VHF-21/22 (A/B) Control Circuit, Block Diagram



then transferred to the µP on an 8-bit parallel data bus. The analog voltages that can be measured and their 3-bit addresses are listed below. ANALOG VOLTAGE Tuning volts +5-V dc power supply +12-V dc power supply Forward power AGC voltage Receiver RF injection level Reflected power Transmitter temperature



ADDRESS 0 0 0 0 1 1 1 1



0 0 1 1 0 0 1 1



0 1 0 1 0 1 0 1



4.6.3 Frequency Synthesizer (R efer to Figure 4-6, Figure 5-20, and Figure 6-31 thru Figure 6-38) The frequency synthesizer provides the transmitter excitation, receiver injection, and the receiver preselector tune voltage. The synthesizer, shown in Figure 4-6, consists of a voltage-controlled oscillator (vco) in a phase-locked loop that is controlled by an LSI digital synthesizer IC. Frequency select data is provided to the digital synthesizer IC by the microprocessor. Frequency stability is determined by a 6.4-MHz crystal oscillator. Basically, the phase-locked loop consists of the voltage-controlled oscillator, a variable-ratio divider consisting of a dual-modulus prescaler and two counters (A and N), a frequency/phase detector, a 25-kHz reference frequency, and a low-pass filter.



Revised 1 October 2001



4-14



theory of operation 523-0771858



Figure 4-6. VHF-21/22 (A/B) Synthesizer Circuit, Block Diagram



The output of the vco, which is the output of the synthesizer, is applied to the input of the variable-ratio divider, where it is divided by the ratio R. (The ratio R is determined by the microprocessor from the operating mode and active frequency of the transceiver.) The variable-ratio divider provides an output pulse for every R cycle of the vco frequency. The output pulses from the divider are compared with the 25-kHz reference by the frequency/phase detector. The frequency/phase detector provides an error signal whenever the divider output is not 25 kHz or is not in phase with the reference frequency. The error output of the detector is applied through the low-pass filter to control the vco. The low-pass filter sums the error pulses from the detector to provide a dc tune voltage for the vco. The ratio R, provided by the variable-ratio divider, can be calculated by dividing the desired vco operating frequency by 25 kHz. The ratio R varies from 4720 at 118 MHz (lowest transmit frequency) to 6321 at 158.025 MHz (highest receiver injection frequency). The variable-ratio divider does not use the ratio R directly but arrives at the same result by using a prescaler that first divides the vco frequency into 41-cycle or 40-cycle increments. The required number of 41-cycle increments plus the number of 40-cycle increments are then added together to obtain the ratio R. For example, if the desired vco frequency is 118.025 MHz, it takes one 41-cycle increment plus 117 40-cycle increments to equal 4721, which is also equal to 118.025 MHz divided by 25 kHz. The number of 41-cycle increments can vary from 0 to 39 and corresponds to the number of 25-kHz increments selectable in each 1-MHz segment to which the synthesizer can be tuned. This number is stored by the microprocessor into one of two down counters (A counter) in digital synthesizer IC U401. The other down counter (N counter) is loaded with the total number of 40-cycle and 41-cycle increments which correspond to the MHz portion of the selected frequency (118 through 158.025 MHz).



Revised 1 October 2001



4-15



theory of operation 523-0771858 The divide operation begins when the A and N counters in U401 are loaded. If the contents of the A counter is greater than zero, a logic 0 is sent to pin 1 of dual-modulus prescaler U403, causing it to divide the vco frequency into 41-cycle increments. After each 41-cycle increment, the prescaler sends a logic 1 pulse to pin 10 of U401 to decrement both the A and N counters. When the A counter is decremented to zero, a logic 1 is applied to pin 1 of U403, causing it to divide the vco frequency into 40-cycle increments. The process continues until the N counter is decremented to zero. A logic 1 pulse is then applied to the frequency/phase detector in U401 and both counters are reset to their original values, starting a new divide cycle. The divide operation is continuous and results in a series of pulses being applied to one input of the frequency/phase detector. The 25-kHz reference frequency is applied to the other input of the frequency/phase detector. The 25-kHz reference frequency is derived within the digital synthesizer IC by dividing the 6.4-MHz crystal oscillator output by 256. The reference frequency also establishes the minimum frequency spacing (or channel spacing) between selectable frequencies (or channels). Variable capacitor C422 provides fine adjustment of the 6.4-MHz oscillator frequency. The frequency/phase detector has two outputs, φV and φR, that provide error information. If the divided down vco frequency or phase is greater than 25 kHz, then φR is high and φV is pulsed low. If the divided down vco frequency or phase is less than 25 kHz, then φR is pulsed low and φV remains high. When the frequency and phase of the divided down vco frequency are equal to the 25-kHz reference, φR and φV remain high except for brief periods every 40 µs when both are pulsed low. The outputs of the frequency/phase detector are applied to integrator U402, and an 8-kHz low-pass filter. The output of the low-pass filter is the dc tune voltage applied to the vco and to the receiver tune voltage amplifier U404A. The normal range of the dc tune voltage at test point TP8 is from +5.0 V dc at 118 MHz to +20 V dc at 158 MHz (138 MHz in receive mode). The vco is a series tuned Colpitts oscillator (Q405) with two buffer stages (Q410 and Q403). The output frequency of the vco is determined by the dc tune voltage applied to varactor CR403 by the low-pass filter. Variable capacitor C415 and inductor L406 provide adjustment of the tune voltage at high and low frequencies, respectively. The buffered output of the vco is applied to the first mixer stage in the receiver, the transmitter power amplifier, and through Q406 to the input of dual-modulus prescaler U403, which is the first stage of the variable ratio divider. Transistor switches Q401 and Q402 control the vco output applied to the transmitter and receiver, respectively. These switches are controlled by the transmit key line and a synthesizer-locked signal to prevent simultaneous operation of the receiver and transmitter, and to prevent operation of both the receiver and transmitter while the vco is tuning. 4.6.4 Receiver Circuit (Refer t o Figure 4-7 and Figure 6-14 thru Figure 6-21) During the receive mode the antenna signal is applied to the receiver preselector through forward biased T/R diode CR602. The preselector consists of four identical parallel resonant RF filters. Each filter consists of an inductor, a capacitor, and two varactors (voltage variable capacitance diodes). Tuning voltage for the varactors is provided by the synthesizer and varies from +5.0 V dc at 118 MHz to +20.0 V dc at 151.975 MHz. The preselector attenuates undesired signal components to control spurious responses. A variable capacitor and variable inductor in each preselector is used to tune each preselector at high and low frequencies respectively. The output of the preselector is applied to pin-diode attenuator CR209, which is controlled by the RF AGC signal and provides up to 25 dB of attenuation in the presence of strong RF signals. The pin-diode attenuator can also be controlled externally in early models of the VHF-22( ). A separate pin-diode attenuator, CR211, is provided in later models of the VHF-22( ) for external control. This external control is used in dual-comm in-



Revised 1 October 2001



4-16



theory of operation 523-0771858



Figure 4-7. VHF-21/22 (A/B) Receiver Circuit, Block Diagram



stallations, where one transceiver is operated in the transmit mode while the other transceiver is simultaneously used to monitor a different receive frequency. The output of pin-diode attenuator CR209 is applied along with the injection signal from the synthesizer to dual-junction FET mixer Q201 to obtain the first IF signal. The high-side injection frequency varies from 138.025 MHz at receive frequency 118 MHz to 158.025 MHz at receive frequency 138.000 MHz to obtain a first IF frequency of 20.025 MHz. Those transceivers with extended frequency range also use low-side injection (118.000 to 131.950 MHz) to extend the receive frequency up to 151.975 MHz. The output of the first mixer is applied through 20.025-MHz crystal filter FL201 to the first IF amplifier, Q202. Filter FL201 is the only component that is different in the wide-band and narrow-band receivers; it is an 8-pole, 1800-ohm filter in the wide-band receivers and a 10-pole, 1800-ohm filter in the narrow-band receivers. The output of the first IF amplifier is applied to a second IF amplifier before being applied to a second 20.025-MHz filter, FL202. AGC voltages are applied to both Q202 and Q203 for further gain reduction in the presence of strong RF signals. The combined voltage gain of Q202 and Q203 is approximately 25 dB with no AGC signal. Variable capacitors C218, C220, C228, and C230 are used to adjust the 20.025-MHz IF circuits for maximum AGC voltage.



Revised 1 October 2001



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theory of operation 523-0771858 The output of the second IF filter is applied to the second mixer, Q204, along with a 1-V, 19.57-MHz injection signal to obtain the 455-kHz second IF signal. The 19.57-MHz low-side injection signal is provided by crystal-controlled local oscillator Q205. The power gain of the mixer is approximately 12 dB. The resultant 455-kHz output of the mixer is amplified by the 2-stage linear IF amplifier IC, U201. U201 provides approximately 80 dB of power gain. AGC is applied to both stages for gain reduction in the presence of strong received signals. The output of IF amplifier U201 is applied to a class-B transistor detector, Q206. Since Q206 is biased on the verge of conduction, it provides both half-wave rectification (detection) and amplification of the audio signal. The output of the detector is applied to the inverting input of IF AGC amplifier U202B, where it is compared with a +6.5-V dc reference. The average dc output of the detector must be less than this reference before the AGC amplifier begins to reduce receiver gain. During normal operation, the amplified RF noise with no input signal is enough to lower the average output voltage of the detector and cause AGC gain reduction to occur. This ample-gain concept ensures that receiver performance remains satisfactory as components age. The output of IF AGC amplifier U202B is applied to both 455-kHz IF amplifiers, the source of both 20.025MHz IF amplifiers, the carrier squelch circuit, and to the inverting input of RF AGC amplifier U202A. The output of the RF AGC amplifier varies from 0 V dc with a strong signal to +8 to +10 V dc with a weak signal, and is applied to pin-diode attenuator CR209 and to gate 2 of both 20.025-MHz IF amplifiers. The application of AGC to both the gate and the source of the 20.025-MHz IF amplifiers extends the attenuation range of each amplifier to approximately 30 dB. 4.6.5 Automatic Squelch Circu its (Refer to Figure 4-8 and Figure 6-14 thru Figure 6-21) Two automatic squelch circuits are used in the receiver. The noise squelch circuit is sensitive to the phase noise normally received when no signal is present and opens the squelch switch when the noise exceeds the noise threshold. The carrier squelch circuit is sensitive to the output of the IF AGC amplifier and closes the squelch switch when the received carrier exceeds 20 µV. 4.6.5.1 Noise Squelch Circuit (R efer to Figure 4-8 and Figure 6-14 thru Figure 6-21) The noise squelch circuit consists of high-gain limiting amplifier U306A, quadrature detector U306B, audio amplifier U306C, high-pass filter U307A, diode detector CR304, and comparator U304A. U306A, B, and C are contained in a single multifunction FM IF IC. The noise squelch circuit receives its input from the third IF amplifier, U201A. This signal is amplified and limited by the high-gain FM IF amplifier to eliminate any amplitude variations before it is applied to the quadrature detector. Quadrature detector U306B converts any FM or phase noise on the received signal to an audio frequency noise signal. Variable inductor L301 is used to tune the quadrature detector for a maximum noise signal with no RF input applied to the transceiver. This noise signal is then filtered by high-pass filter U307A to remove any low-frequency voice components resulting from the residual FM present in many comm transmitters. The filtered noise signal is detected by diode CR304 and filtered by C323 to obtain a dc voltage proportional to the phase noise level. The resulting dc noise signal is applied to comparator U304A along with the noise threshold established by potentiometer R345. The output of the comparator is approximately +12 V dc when the dc noise signal is less than the noise threshold, and approximately 0 V dc when greater than the threshold. The positive output from the comparator turns on squelch switch U302C in the receiver audio circuit (Figure 4-9) and applies the receiver audio signal to the audio output amplifier. The noise squelch threshold is normally adjusted so that a 3-µV carrier signal will cause the squelch switch to close. 4.6.5.2 Carrier Squelch Circuit (Refer to Figure 4-8 and Figure 6-14 thru Figure 6-21) The carrier squelch circuit, consisting of U304B and U307B, closes squelch switch U302 whenever the received carrier signal exceeds 20 µV. The carrier squelch circuit receives its input signal directly from IF AGC



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ROCKWELL COLLINS INSTRUCTION BOOK (REPAIR MANUAL) VHF-21( )/22( ), VHF Comm Transceiver VHF-21( )/22( ) VHF Comm Transceiver INSTRUCTION BOOK (REPAIR MANUAL) (523-0771854, 3RD REVISION, DATED JUL 30/02)



TEMPORARY REVISION NO. 23-12-10-10 Insert facing page 4-19, 23-12-10. Subject: Miscellaneous corrections. The fourth line down from the top of page 4-19 reads in part “…to drive NOR gates U306A, B, and C.” This portion of text is corrected as “…to drive NOR gates U305A, B, and C.” This correction puts the text and the schematic (Figure 6-15) in agreement.



Temporary Revision 10 523-0771854-3A911A



23-12-10



Page 1 of 5 Mar 30/05



theory of operation 523-0771858 amplifier U202B. The AGC signal is applied to amplifier U307B along with the carrier threshold established by R328. Amplifier U307B provides a positive output when the AGC signal is more positive than the threshold. U304B is a comparator with hysteresis that converts the output of U307B to zero and 12-V dc logic levels to drive NOR gates U306A, B, and C. The NOR gates permit either the noise squelch, carrier squelch, or the external squelch test signal to close squelch switch U302C. The NOR gates also prevent closing the squelch switch during the transmit mode.



Figure 4-8. VHF-21/22 (A/B) Squelch Circuits, Block Diagram



4.6.6 Receiver Audio Circuits (Refer to Figure 4-9 and Figure 6-14 thru Figure 6-21) During the receive mode, the detected receiver audio is applied through an active audio filter, the compressor circuit, and the squelch switch to the audio output amplifier. Audio filter U301 is an active low-pass filter that amplifies the speech components in the received signal and attenuates any higher frequency audio components. The compressor circuit, consisting of U308B, Q301, and Q302, has a very limited range and helps to smooth out the variations in speech levels between various received signals. The compressor can be disabled by a jumper to ground on circuit card A2 or, in the VHF-22( ), by a jumper to ground at rear connector pin 9. The compressor output is applied through the squelch switch to audio output amplifier U303 along with the transfer tone from the microprocessor and a sidetone signal from the transmitter. The output level of U303 can be adjusted for specific installations by audio level controls R318 (receive audio), R323 (transfer tone), and R325 (sidetone). Three audio output signals (receiver audio, sidetone, and combined receiver audio and sidetone) are provided to meet the requirements of various installations. Maximum output power of the audio amplifier is 100 mW with a 3-µV RF input signal. Sidetone switch U302A is provided in units with Service Bulletin No 5 to increase the isolation between the receiver and transmitter circuits. The increased isolation eliminates any DME-to-comm interference during the receive mode. The detected receive output is also applied to SELCALä amplifier U308A, which provides an unprocessed audio output that can be used by a selective calling decoder or direction-finding equipment. The SELCALä amplifier can provide a 0.5-V rms signal with a 3-µV RF input signal.



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theory of operation 523-0771858



Figure 4-9. VHF-21/22 ( ) Receiver Audio Circuits, Block Diagram



4.6.7 Transmitter Circuit (Ref er to Figure 4-10, Figure 6-51, Figure 6-52, or Figure 6-57) The transmitter is a 4-stage broadband solid-state circuit that amplifies the +20-dBm synthesizer output to an RF output of 16 watts minimum. The first stage, Q601, of the transmitter is a class-A amplifier and the final three stages, Q602, Q603, and Q604, are class-C amplifiers. The first two stages are powered directly from the +16-V dc transmitter power bus. Driver stage Q603 is powered from the +16-V dc transmitter power bus with limited collector modulation, while power amplifier Q604 receives all of its power from the modulator. Output tuning is provided by variable capacitor C650, which is normally adjusted for maximum RF output power at the highest frequency that the transmitter is to be used on. The output is low pass filtered to reject harmonics of the carrier. Modulation limiting is provided by the circuit consisting of R618, CR606, CR607, and R619 to prevent overmodulation of the RF output. This circuit applies collector modulation to driver Q603 through CR607 except when the modulation voltage drops below the +16-V dc transmit bus. When the modulation voltage drops below +16 V dc, CR607 is reverse biased and CR606 is forward biased so that part of the +16-V dc transmit bus voltage is applied to the collector of Q603. This permits Q603 to conduct even though Q604 may be cut off by low modulation voltage. Normal leakage through Q604 ensures that some RF is applied to the antenna to prevent overmodulation. During the receive mode, T/R switch diodes CR601 and CR602 are forward biased and provide a path for the received signal from the antenna to the receiver preselector. CR601 provides a virtual ground in the lowpass filter to help isolate the antenna from the final stage of transmitter Q604. During the transmit mode, the +16-V dc transmitter power reverse biases CR601 and CR602 to disconnect the antenna from the receiver.



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theory of operation 523-0771858



Figure 4-10. VHF-21/22 (A/B) Transmitter, Simplified Schematic Diagram



Forward and reverse transmit power is sampled through hot-carrier diode detectors CR603 and CR604, connected to transformer T603. The forward and reverse power signals are monitored by the microprocessor to ensure proper operation of the transmitter. The forward power signal is also used to provide the sidetone signal applied to the receiver audio output amplifier. U601 is a temperature-controlled current source that provides the microprocessor with the operating temperature of the RF power amplifier. 4.6.8 Modulator Circuit (Refe r to Figure 4-11 and Figure 6-25 thru Figure 6-27) The modulator circuit consists of an audio compressor, a comparator, and a switching amplifier with lowpass filtering of the output. The modulator circuit provides the modulated dc power for the RF amplifiers in the transmitter. During the transmit mode, the 5-V XMIT signal from the microprocessor is converted to a +12-V logic signal by level converter U507A. The 12-V XMIT signal turns on the 106.7-kHz triangle-wave generator, U506. This signal is also applied to the squelch circuits on receiver circuit card A2 to prevent the squelch from opening. The triangle-wave generator is an integrating amplifier that is controlled by a 106.7-kHz square-wave signal which is provided by the control circuits on control/synthesizer circuit card A4. The output from the trianglewave generator is a 2-Vp-p signal with approximately +6 V dc bias. The triangle-wave signal is applied to the comparators in the +16-V dc transmit power supply and the modulator, causing them to become operational.



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theory of operation 523-0771858



Figure 4-11. VHF-21/22 (A/B) Modulator Circuit, Block Diagram



The audio compressor, consisting of U501A, Q501, and Q509, ensures that proper modulation depth is maintained with different microphone signal levels. This is achieved by automatically varying the gain of operational amplifier U501A with the active feedback loop consisting of Q501 and Q509. When the output of U501A exceeds the threshold established by the biasing circuit on Q501, Q501 begins to conduct. This causes Q501 to draw current through R523, which lowers the gate bias on Q509. This reduces the source-to-drain impedance of Q509, which reduces the gain of U501A and limits its output to prevent excessive modulation depth. Potentiometer R510 is provided to compensate for high or low output microphones and is normally set so that compression begins when the microphone output is at 125 mV rms. The output from the compressor is applied through modulation depth control R519 to the inverting input of U502A, where it is superimposed on the dc bias voltage provided by transmit power control R520. This dc biased audio signal is compared with the 106.7-kHz triangle-wave signal by U502A to generate a 4.5-Vp-p, 106.7-kHz, pulse width modulated signal. The dc feedback bias provided by R520 determines the average pulse width of the square wave, while the audio signal causes the pulse width to vary according to the amplitude of the audio signal. Resistor R517 provides the feedback required to hold the output power constant over the entire band. The output from the comparator is applied to the switching amplifier, Q503, Q504, and Q506, which provides a 25-Vp-p pulse width modulated signal to low-pass filter L501 and associated capacitors. The low-pass filter averages the +25-V pulses to provide the modulated dc required by the RF power amplifiers in the transmitter. The modulator is turned off during the receive mode by disabling the triangle-wave generator, which prevents the transistors in the switching amplifier from turning on. This causes the output of the modulator to be 0 volt and prevents operation of the RF power amplifiers in the transmitter.



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theory of operation 523-0771858 The +16-V dc transmit power supply, consisting of U502B, Q502, and Q507, is a switching regulator. The switching frequency of the regulator is determined by the 106.7-kHz triangle-wave signal. Voltage regulation is provided by varying the pulse width of the drive signal applied to the switching transistors. The pulse width of the drive signal is controlled by U502B, which compares the feedback signal provided by voltage divider R524 and R525 with the triangle-wave signal. The 4.5 Vp-p output of U502B is amplified by Q507 and Q502 to approximately 25 Vp-p. L502 and C514 provide energy storage and ripple filtering for the +16-V dc output. Resistor R509 and diode CR501 ensure that the +16-V dc power supply is turned off during the receive mode by holding pin 6 more positive (+4 V dc) than pin 5 (+1.2 V dc) when the triangle-wave generator is turned off. 4.6.9 Power Supply Circuits (R efer to Figure 4-12 and Figure 6-25 thru Figure 6-27) Primary dc power for the transceiver is applied through interface circuit card A1 to power supply/modulator circuit card A3, where it is filtered by L503, C506, C507, C519, and C528 before it is applied to any other circuits. The input filter provides both inductive and capacitive filtering to the primary power. The filtered primary power is applied directly to the switching amplifier in the modulator, the +16-V dc transmitter power supply, and to an overvoltage protection circuit.



Figure 4-12. VHF-21/22 (A/B) Power Supply Circuit, Block Diagram



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theory of operation 523-0771858 The overvoltage protection circuit, consisting of Q505, Q510, Q511, and VR510, turns off the power supplies when the primary supply voltage exceeds +36 V dc. This circuit also turns off the primary power if the output of either +12-V dc regulator or the main +5-V dc regulator should exceed a predetermined limit. During normal operation (less than +36-V dc input power), transistors Q510 and Q511 are biased off by resistor R544. This allows Darlington transistor Q505 to turn on and provides dc power to the voltage regulators and other circuits in the transceiver. If the primary power exceeds +36 V dc, zener diode CR510 begins to conduct and turns on transistor Q511. The current flowing through Q511 increases the bias voltage across R534, which turns transistor Q505 off. If the output of one of the voltage regulators exceeds its associated zener voltage, the current through the zener diode turns on transistor Q510. This turns on transistor Q511, which turns off transistor Q505. The +5-V dc and +12-V dc voltage regulators are 3-terminal series regulator ICs with capacitive filtering on the outputs. The +5-V dc regulator (U407) on circuit card A4 provides regulated power only for synthesizer IC U401. The +5.12-V dc regulator (U708), also located on circuit card A4, provides a precise voltage reference for a/d converter U707. Potentiometer R708 provides fine adjustment of the output voltage level of the +5.12-V dc regulator. +23-V dc, 3-terminal voltage regulator U405 is provided on circuit card A4 to supply well regulated power to the tune-voltage amplifiers in the synthesizer circuit. This voltage regulator receives unregulated power from a voltage boost circuit that ensures adequate tune voltage during emergency low-voltage operation. The voltage boost circuit, Q701, Q702, and Q704, adds +12 V dc to the input voltage (nominally +27 V dc). Drive for the circuit is obtained from the ALE output of the microprocessor, which results in a drive frequency of 213.3 kHz. When the ALE signal is high, Q701 and Q704 are turned on, Q702 is turned off, and capacitor C713 charges to approximately +26 V dc through CR701 and Q701. When the ALE signal is low, Q701 and Q704 are turned off and Q702 is turned on. This replaces the ground at the on side of C713 with +12 V dc and raises the voltage at the other side of C713 to approximately +37 V dc. The voltage on C713 forward biases CR702 and charges filter capacitor C705 to +34 V dc or more. The voltage on C705 ensures that there is sufficient voltage available for the +23-V dc regulator. 4.6.10 Filter Assembly Circuits (Refer to Figure 4-7, Figure 4-10, and Figure 6-58) Filter assembly A8 is used to reduce FM interference caused by high-power FM radio stations. The filter has two sections. The first section consists of A8C101, C102, C103, L101, and L102. These components are connected between the antenna jack, P101-A1 or J102 and A5J611. The second part consists of A8C104 thru C108, L103, and L104. These components are connected from the output of T/R switching diodes A5CR601 and CR602 to the input to the preselector on the A2 receiver card. A8C108 is adjustable to minimize input signals around 102 MHz. 4.7 VHF-21/22(C/D) FUNCTI ONAL THEORY OF OPERATION (REFER TO FIGURE 4-13) 4.7.1 Interface Circuits All input and output signals to the comm transceivers are applied through the rear connector and interface circuits on CCA A1. Two different A1 assemblies are used; one has a DPA rear connector and is used with the VHF-21( ), and the other has a Collins Thinline connector and is used with the VHF-22( ). The interface circuits on both A1 assemblies provide noise filtering, transient protection, serial output data buffering, and parallel-to-serial input data conversion. 4.7.2 Control Circuits Overall control of the comm transceiver is provided by a single 16-bit microprocessor located on the A4A1 control card, part of the A4 synthesizer CCA. All pilot initiated commands entered via the associated panel-



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theory of operation 523-0771858 mounted comm control and the mic button are connected through the interface circuits on A1 to the microprocessor on the A4A1 control card. The microprocessor interprets these commands to determine the operating mode and frequency of the transceiver. The microprocessor also monitors selected parameters within the transceiver to ensure that each is within a predetermined range. If an out-of-limit condition is detected, the microprocessor sends an audible alert (two tone bursts of approximately 800 Hz) to the audio system, and may interrupt a transmission if a critical fault is detected during the transmit mode. A single 800 Hz burst is generated when the channel data is switched from active to preset at the control head or FMS.



Figure 4-13. VHF-21/22 (C/D) VHF Comm Transceiver, Block Diagram



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theory of operation 523-0771858 4.7.3 Frequency Synthesizer The frequency synthesizer is comprised of three custom large scale integration (LSI) circuits and supporting components. The circuit phase locks the voltage controlled oscillator (VCO) selected by the operating conditions to the 19.6 MHz temperature compensated crystal oscillator (TCXO). This gives every channel the stability of the TCXO. The synthesizer provides the 118.000- to 151.975-MHz excitation for the transmitter and both the 138.025- to 158.025-MHz high-side and 118.000- to 131.950-MHz low-side injections for the receiver first mixer. All channels are selectable in increments of 8.333 kHz. The frequency synthesizer used in the VHF-21/22 (C/D) utilizes a proprietary approach to fractional-N synthesis, allowing these radios to meet stringent adjacent channel performance while maintaining the advantages of a single loop phase locked loop (PLL) synthesizer. Fractional-N techniques reduce phase noise and allow wider loop bandwidths, aiding in the suppression of vibration-induced microphonics. 4.7.4 VCO Assembly The VCO assembly is a shielded module mounted on the A4 synthesizer CCA. It consists of two VCOs built into shielded cans, along with switching and amplification required for operation in the VHF comm transceiver. The VCO assembly also contains the modulator which creates the low-level AM modulation used in conjunction with the modulation control loop. The low VCO tunes from 118.000 to 138.000 MHz, while the high VCO tunes from 138.000 to 158.000 MHz. In a VHF-21/22 (C), the high VCO is used for receive local oscillator (LO) (high-side injection) while the low VCO is used for the transmit LO (low-side injection). In a VHF-21/22 (D), the same VCOs are used for the regular aeronautical band, but when the transceiver is used between 138 and 158 MHz, the VCOs are switched: the high VCO becomes the transmit LO, and the low VCO becomes the receive LO injection. The receiver switches from high-side to low-side injection. 4.7.5 Receiver The receiver is a dual-conversion superheterodyne type with IF frequencies of 20.025 MHz and 450 kHz. Frequency conversion is performed by two mixer circuits. The first is a dual JFET mixer with either highside or low-side injection from the synthesizer, and the second is a dual-gate MOSFET mixer with injection from a 19.575-MHz crystal-controlled local oscillator. Four varactor-tuned preselector filters provide RF selectivity. The channel bandwidth and IF selectivity is determined by two 20.025-MHz crystal filters. The crystal filters are switched depending on the mode the operator selects. On a conventional 25-kHz channel, the receiver will use a wider crystal filter than it does for an 8.33-kHz channel. The switching is controlled by the control circuits on the A4A3 control/synthesizer card, and the filters are located on the A3 power supply/modulator card. By entering the desired channel for operation, the pilot selects the mode and filter that will be used. A 450-kHz IF amplifier IC provides approximately 80 dB of IF gain prior to detection. The audio signal from the detector is applied to the receiver AGC circuits, the automatic squelch circuit, and the audio output amplifiers. Multiple AGC circuits hold the receiver output constant over a wide range of RF signal levels. Filter assembly A8 reduces FM interference caused by high-power FM radio stations. 4.7.6 Automatic Squelch Circu its Two automatic squelch circuits are used in the transceiver: carrier squelch and noise squelch. The carrier squelch is derived from the receiver AGC voltage and is used to open the squelch when multiple carriers are



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theory of operation 523-0771858 received. The noise squelch circuit uses the detected AM that will be used for output audio, and processes it to amplify noise beyond the range of human speech, but still present in the audio output. Separate controls are provided for setting the squelch opening point for 8.33-kHz and 25-kHz mode channels. 4.7.7 Transmitter The transmitter is a broadband solid-state circuit excited by the synthesizer output. Minimum unmodulated output power is 16 watts over the frequency range from 118.000 to 151.975 MHz. One class A stage, two class AB stages, and one class C stage provide the necessary amplification. The drive to the transmitter is low-level modulated on the VCO assembly (part of the A4 synthesizer CCA), under control of the A3 power supply/modulator. Output from the transmitter is sampled by a directional coupler on the A3 assembly and this sample is used to regulate the drive to the transmitter. The transmitter incorporates a three section lowpass filter to attenuate harmonic energy, and the transceiver contains additional lowpass filtering in the A8 module before signal reaches the antenna port. 4.7.8 Modulator Circuit The modulator in the VHF-21/22 (C/D) transceiver uses low level modulation, and a feedback control system to prevent overmodulation of the carrier during audio peaks. Unlike conventional AM transmitters, and earlier versions of this transceiver, modulation is done well before the final amplifiers. The control circuit functions by comparing the detected envelope of the RF waveform with the modulating audio input, and varying the drive to the PA to match the envelope to the audio. The incoming audio from the user’s microphone is compressed by an audio compressor. This circuit reduces the peak to average ratio of the audio applied to the modulator, allowing more consistent modulation percentage, and accommodating variation between microphones. This audio signal is then lowpass filtered and applied to circuitry that varies its dc level and the magnitude of its peak to peak swing. The carrier produced by the A4 synthesizer assembly is modulated in a double-balanced mixer. The output from the modulator is amplified in the A5 transmitter and routed to the antenna. Before leaving the radio, the output is sampled by a directional coupler on the A3 power supply/modulator. The sampled carrier is envelope detected, yielding an ac audio frequency signal that corresponds to the modulation. This signal is then compared to the audio input and an error signal is derived that corrects the modulation by controlling the voltage to the double-balanced mixer. The modulation control loop allows precise setting of average power, peak envelope power, and the limitation of both positive and negative modulation peaks. These adjustments are not accessible to the user. The circuit will turn down the output power if the antenna is disconnected or damaged, thus reducing the danger of damage to the PA, or the risk of transmitting distorted modulation. 4.7.9 Power Supply Circuits The power supply circuits on the A3 power supply/modulator card consist of an LC power line filter, an overvoltage protection circuit, two +12-V dc linear regulators, a +5-V dc linear regulator, a +16-V dc linear regulator, and switching voltage inverters to generate -5-V and -10-V dc at low current. These circuits provide power for all the of the circuits in the transceiver, except for the synthesizer components on the A4 CCA. The synthesizer has its own voltage regulators. 4.8 VHF-21/22 (C/D) DETAIL ED THEORY OF OPERATION 4.8.1 Interface Circuits (Refer to Figure 4-4 and Figure 6-13) All input and output signals to the transceiver are applied through the rear connector and interface circuits on circuit card A1. Different interface circuit cards are used in the VHF-21( ) and VHF-22( ) due to the different rear connectors. The major differences between the two circuit cards are the power relay provided



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theory of operation 523-0771858 only in the VHF-22( ) and the serial/parallel select logic. Both of these differences are caused by the smaller number of pins available in the rear connector on the VHF-21( ). The power relay in the VHF-22( ) is controlled by a low-current input from the comm control. Both terminals of the relay coil are available at the unit connector so that the transceiver power can be controlled by either a switched +28-V dc signal or a switched ground signal. In the VHF-22( ), the serial/parallel select logic consists of a single rear connector pin (P101-32) that is connected through an RC filter and the parallel-to-serial converter to the microprocessor. Grounding the serial/parallel select pin on the VHF-22( ) causes the microprocessor to take frequency data from the serial tuning control. When this pin is open, the frequency data is taken from the parallel (2-out-of-5) control. Both types of controls can be connected to the transceiver simultaneously, with the state of the serial/parallel select pin determining the tuning source. The serial data output in the VHF-22( ) is always active and provides active frequency and diagnostic information back to the serial tuning control, even when the frequency is determined by the parallel control. Also, when both type controls are connected, the transceiver responds to squelch control from either control and responds to the self-test command from the serial control, even when operating in the parallel mode. Additional serial/parallel select logic is required in the VHF-21( ) because the serial and parallel modes share several of the same rear connector pins and cannot function independently as they can in the VHF22( ). This circuit monitors three of the parallel frequency data lines, and provides a signal to the microprocessor and enables the serial data buffers when the serial mode is selected. The serial data mode is selected when all three of the monitored parallel data lines are grounded simultaneously. This combination of parallel bits would be an invalid 2-out-of-5 code and would never occur legitimately in a parallel-tuned installation. The serial data output buffer is active only when the transceiver is strapped for serial tuning. The serial data received and transmitted by the VHF-21( )/22( ) conforms to the CSDB (Commercial Standard Digital Bus) format. A non-return-to-zero synchronous transmission is used with one start bit, eight data bits, an odd parity bit, and one stop bit. This group of data is called a byte. A logic 1 is defined as line A positive with respect to line B, and a logic 0 is defined as line B positive with respect to line A. The start bit is always a logic 0 and the stop bit is always a logic 1. The data transmission rate is approximately 12.5 Kbits/second with a refresh rate of approximately 10/second. Data transferred on the comm serial bus is organized in blocks of six bytes. The first block in a transmission must be a sync block consisting of six hexadecimal A5 characters. Each subsequent data block consists of a label byte, a status byte, and four message bytes. The data within each byte is transmitted with the least significant bit first. All parallel frequency data lines and some of the input control lines are filtered by RC filter circuits with pullup resistors connected to +12 V dc. All of these input data lines except the squelch disable and keyline are applied to a parallel/serial converter consisting of two 8-bit shift registers. The data applied to the shift register is periodically latched in the registers by a strobe signal from the microprocessor. The data is then shifted from the registers by clock pulses from the microprocessor. The 17 bits of data available from the parallel-to-serial converter are defined as follows:



BIT



DEFINITION



0 1 2 3 4



1 = parallel tune, 0 = serial tune Unit identification A Unit identification B 10 MHz A 10 MHz B



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theory of operation 523-0771858 BIT



DEFINITION



5 6 7 8 9 10 11 12 13 14 15 16



10 MHz C 1 MHz A 1 MHz B 1 MHz C 1 MHz D 0.1 MHz A 0.1 MHz B 0.1 MHz C 0.1 MHz D 0.01 MHz C 0.01 MHz D Upper frequency limit (VHF-21C/22C only)



The 2-out-of-5 frequency Select Code used for parallel tuning is defined below. FREQ DIGIT 10, 1, 0.1 MHz



2-OUT-OF-5 CODE A B C D



0 1 2 3 4 5 6 7 8 9



1 0 0 1 1 1 1 1 0 0



0 0 1 0 0 1 1 1 1 1



1 1 0 0 1 0 0 1 1 1



1 1 1 1 0 0 1 0 0 1



1 0 0 1



1 1 0 0



kHz 00 25 50 75



All input and output audio signal lines are filtered to suppress noise entering or leaving the transceiver. 4.8.2 Control Circuits (Refer t o Figure 4-14, Figure 6-40 and Figure 6-41) The A4A1 control card contains the synthesizer frequency control circuits. The frequency controller takes the tuning data applied to the transceiver and converts it to the proper code to be used by the synthesizer. 2-outof-5 tuning data is fed directly to the field programmable gate array (FPGA) U401. CSDB tuning data is fed directly to microprocessor U400 and is sent to the FPGA for further processing. In either case, synthesizer tuning is provided via three data lines outputted by the FPGA and functions to set the synthesizer frequency to the desired receive and transmit local oscillator (LO) frequencies. The FPGA is the discrete I/O interface to the frequency controller and provides the transceiver with discrete control outputs such as Transmit Enable, Receive Enable, etc. A switchable IF filter circuit on the synthe-



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theory of operation 523-0771858 sizer selects the appropriate filter for 8.33-kHz spacing or 25-kHz spacing receiver operation. The FPGA selects the correct filter depending on the frequency input data. When the synthesizer loses lock, the phase frequency detector (PFD) on the A4A3 control/synthesizer card sends a loss-of-lock signal to the FPGA.



Figure 4-14. VHF-21/22(C/D) Control Circuit, Block Diagram



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theory of operation 523-0771858 Timing for the controller is provided by a 19.6-MHz temperature compensated crystal oscillator (TCXO) on the A4A3 control/synthesizer card. The FPGA divides the oscillator frequency by 10 to provide the 1.96-MHz reference frequency for the synthesizer. Program memory for the CPU resides in 2-Mbyte FLASH nonvolatile memory IC U411. The FLASH can be board-level programmed. Data memory is provided by a 128-kbyte RAM (U404). A/D converter U406 provides the frequency controller with analog data such as forward and reflected power. The A/D converter also supplies data to determine the health of the transceiver such as PA heatsink temperature and power supply voltages. The frequency controller also provides D/A converter U415 with data for tuning the receiver’s preselector. The 8-bit data is converted by the controller from the frequency information received from the frequency bus. During normal operation, the microprocessor sends a logic 1 pulse to the watchdog circuit U414 at regular intervals. Failure of the microprocessor to send this pulse causes the watchdog circuit to reset the microprocessor. The microprocessor also monitors selected parameters within the transceiver to ensure that each is within a predetermined range. If an out-of-limit condition is detected, the microprocessor sends an audible alert (two 800 Hz tone bursts) to the audio system and may interrupt a transmission if a critical fault is detected during the transmit mode. A single 800 Hz burst is generated when channel data is switched from active to preset at the control head or FMS. 4.8.3 Frequency Synthesizer C ircuit (Refer to Figure 4-15 and Figure 6-39 through Figure 6-50) The frequency synthesizer provides the receive LO injection to the first mixer on the A2 receiver and the transmit LO to the A5 transmitter. The A4 synthesizer CCA consists of the A4A1 control card, the A4A2 VCO card (part of VCO assembly), and the A4A3 control/synthesizer card. The synthesizer consists of a proprietary three chip set that performs the functions of a new type of synthesizer, a Fractional-N synthesizer. Frequency select data is provided over a three wire bus from the A4A1 control card’s microprocessor. The user’s frequency command is sent to the radio over the data interface from the control head or FMS. Once inside the radio, the A4A1 control card converts the frequency command into the channel programming data and sends the information to the synthesizer as three lines: a data line, a clock line that clocks the data into internal registers in the main PLL chip U704, and a latch line to tell the PLL chip that the data transmission is complete. Frequency stability is determined by the 19.6-MHz TCXO U700. The frequency synthesizer utilizes a proprietary approach to fractional-N synthesis, allowing the VHF-21/22 (C/D) radios to meet stringent adjacent channel performance while maintaining the advantages of a single loop PLL synthesizer. Fractional-N reduces the divider count of synthesizer for a given output frequency, which reduces phase noise and improves adjacent channel performance in both receive and transmit. Further, since it has a higher reference frequency for a given output frequency, Fractional-N allows a wider loop bandwidth. The wider loop bandwidth allows faster settling time when switching channels, and simpler filter designs. A conventional PLL synthesizer produces an output that is an integer (N) multiple of its comparison or reference frequency. Fout = N* Fref where Fout is the output frequency and Fref is the reference frequency. A fractional-N synthesizer, as its name implies, produces an output that is the equivalent of adding a fraction to the N and multiplying that sum times the Fref. In a conventional synthesizer, there is a simple relationship between the reference frequency and the channel spacing; they are the same. In a fractional N synthesizer, this relationship does not hold. The simplest example is referred to as 1-bit fractional N and the simplest method of implementing this is to switch the N divider between N and N+1 every counter cycle. If the switching were done at a much slower rate than the reference period, it would simply cause the PLL to



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theory of operation 523-0771858 change between two adjacent channels. But since the time for one counter cycle is much faster than the PLL can respond, the PLL takes on the average output produced by a counter value of ((N+1) + N) / 2 = (2N+1)/2 = N + ½ and the output frequency is (N + ½)*Fref. It is possible to extend the range of this technique to very small fractional parts, but implemented in this simple way, various problems surface. For example, this method produces a spurious output at ½ of Fref on either side of the desired output carrier. A conventional PLL produces spurious products at Fref, which is twice as far away from the carrier. Filtering the ½ Fref spur (the so-called “fractional spur”) is therefore harder to do. As the value of N goes up, the fractional spur gets progressively closer to the carrier, negating one of the main benefits of the Fractional-N approach; the wider loop bandwidth (since the wider bandwidth will offer less filtering of the now-closer Fractional reference spur). The Rockwell Collins Fractional-N proprietary chip set uses a more sophisticated approach to Fractional N synthesis and eliminates the fractional spur problem. The output of the VCO, which is the output of the synthesizer, is fed into amplifier U710. This assures adequate drive for the programmable prescaler U708. The output from U708 goes into the main PLL chip, U704, which acts as a programmable divider and the controller for U708. The control information from U704 is in four data lines, called PRESC1 through PRESC4 on U704 and N1 through N4 on the prescaler. Many frequency synthesizers use a dual-modulus divider for the prescaler; a divider which divides at one of two different ratios such as 40 and 41 or, more commonly, 32 or 33. This sort of prescaler only requires one control line to tell it which of the two values to divide by. U708 has four lines and is thus capable of 16 different divide values. The exact divider values used are of little use to the technician attempting to troubleshoot this synthesizer. When programmed to some channel, the PRESC1 - PRESC4 control lines will be toggling. The 19.6-MHz TCXO output goes to the field programmable gate array (FPGA) on the A4A1 control card. The FPGA divides the clock by 10 to 1.96 MHz and returns it to the synthesizer. The 1.96 MHz is used as the reference input to the phase/frequency detector (PFD), U702. The variable input to U702 is the divided output from the PLL chip, U704. U702 is a straightforward implementation of a PFD, but it has several outputs. Only one of these is needed and used. It has another type of output, a loss of lock detector, which operates essentially as a phase detector. This output is used to tell the control card that the loop is out of lock.



Figure 4-15. VHF-21/22 (C/D) Synthesizer Circuit, Block Diagram



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theory of operation 523-0771858 Any digital implementation of a phase detector operates by comparing the timing (phase) of the variable pulse’s edge with the reference pulse’s edge. The comparison is made at the reference rate. The PFD’s advantage is better performance when the loop is not locked. Once locked, the PFD output charge pump either sources (provides) or sinks (pulls in) a current pulse. When locked, the ratio of source to sink is essentially the same and the dc voltage at pin 16 is constant, with some products at the reference rate visible. These are filtered by the following circuitry. The error signal from the charge pump is connected to the loop integrator composed of U705 and the associated components. This circuitry essentially sets the dynamic response of the loop; switching time, settling time, and lock time. It also provides some lowpass filtering of the error signal. The loop bandwidth is approximately 2 kHz. R734 and R733 provide a dc voltage to center the output of U705 in its range, since U705 runs from a single supply. After the integrator, the error signal is more commonly called the control or tuning voltage. U706 and its associated components make up a lowpass filter for additional filtering of the control voltage. Its ripple bandwidth is approximately 70 kHz. By the time the voltage reaches the Tune_Volts pin on the VCO assembly, it should be exceptionally clean dc. R716 and C7002 provide one last pole of filtering. The voltage is proportional to frequency here; that is, the higher the tuning voltage, the higher the output frequency. When a phase locked loop is out of lock, the tuning voltage is generally at one supply limit or the other; in this case, either around +1.5 V dc or +20 V dc. In normal operation, if the variable frequency (VCO) at the PFD is lower in frequency than the reference, the loop will act to pull the frequency up. In this system, that is accomplished by raising the voltage. So if the loop thinks the reference is low, it will bang the control voltage to the positive supply limit. If the oscillator does not come up to frequency, the voltage will stay at the positive limit. Likewise, if the divided VCO frequency at the PFD is too high, the loop will pull the tuning voltage to the negative supply limit. The negative supply is ground in this case and the output of U706 can go as low as about +1.5 V dc. When troubleshooting, it is almost always helpful to open the loop by removing the jumper resistor R743. Apply a variable dc voltage to the tune voltage pin on the VCO and monitor its output with a spectrum analyzer. If the VCO is running, vary the tuning voltage and verify that the VCO tunes higher in frequency with higher dc applied and lower in frequency with lower dc applied. Note The supply voltage is not clean enough to receive signals with, or to look closely at on a spectrum analyzer, but should be adequate to determine that the VCO is running. A 12-V battery and a variable resistor is a good method for generating this tuning voltage. If the output is present, has a good amplitude (the signal at U708 pin 9 should be approximately 1 V p-p), and tunes properly with changes in the tuning voltage, the problem is likely to be elsewhere in the circuitry. Monitor the output of U706 with an oscilloscope or voltmeter. Set the radio to some frequency, near midband is adequate, and set the tuning volts to its minimum. The output of U706 should be pulling high (at the positive limit). Now vary the tuning voltage until the frequency goes above the programmed channel. The output of U706 should go to the negative supply limit. If this behavior doesn’t occur or is improper, the digital parts of the circuit may be bad. Make sure that the divided VCO frequency is present at pin 1 of the PFD, U702. When the VCO is close to the tuned frequency, pin 1 should be approximately the same frequency as the reference, 1.96 MHz, a period of approximately 510 nsec. There are other functions on the synthesizer CCA. The critical components have their own voltage regulators: U711 for +12 V dc and U709 for +5V dc. The loop filter opamps U705 and U706 run from a +24-V dc supply generated by voltage boost circuitry on the A4A3 control/synthesizer card. A clock running at approximately 296 kHz from the A4A1 control card is used to drive the switching power supply composed of



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theory of operation 523-0771858 Q700, Q701 and Q702 along with CR700, CR701, C709, C712, and C717. Programmable voltage regulator U707 is used to regulate the new supply. The tuning voltage for the receiver four pole voltage tuned filter is derived by amplifying voltage from the control card in the circuitry of U703. The receiver injection level test point from the VCO assembly is conditioned and applied to the control card. Finally, forward and reverse power sense lines from the transmitter assembly A5 are lowpass filtered and conditioned before being routed to the A4A1 control card for monitoring. 4.8.4 VCO Circuit (Refer to Fi gure 4-16 and Figure 6-42 thru Figure 6-46) The VCO assembly contains the two VCOs used for transmit and receive local oscillator injection, along with switching, amplification, the AM modulator (a double balanced mixer) for low-level modulation, and all other functions required. U10 and U11 are twin VCO modules built into EMI shielded, hermetically sealed, cans. They are unrepairable assemblies. The power is switched to the appropriate VCO by the LOW-BAND (low true) signal from the A4A1 control card driving transistors Q1, Q2, and Q5. The low VCO tunes from 118.000 to 138.000 MHz, while the high VCO tunes from 138.000 to 158.000 MHz. In a VHF-21/22 (C), the high VCO is used for receive LO injection (high-side injection), while the low VCO is used for the transmit LO (low-side injection). In a VHF-21/22 (D), the same VCOs are used for the regular aeronautical band, but when the transceiver is used between 138 and 158 MHz, the VCOs are switched. That is, the high VCO becomes the transmit LO, and the low VCO becomes the receive LO. The receiver switches from high-side to low-side injection.



Figure 4-16. VHF-21/22 (C/D) VCO Circuit, Block Diagram



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theory of operation 523-0771858 Since only one VCO is on at any given moment, the outputs are combined in resistive power combiner composed of R23, R25, and R26. The output is attenuated by another 3 dB and then amplified by U4, a Monolithic Microwave Integrated Circuit (MMIC). This part was chosen for its output saturated power. The level at the output of the amplifier should be +7 dBm (typical); the resistive power split on the output will drop this to +1, with 0 dBm being almost assured. The next stage is a discrete transistor amplifier based on an NPN medium power transistor, Q6, which will provide approximately 17 to 20 dB of gain. The output of this amplifier is switched using PIN diodes CR3 and CR4, along with transistors Q3 and Q4, so that the output is either routed to the RCVR_INJ output or attenuated and routed to the AM modulator, mixer U1. Modulation from the A3 power supply/modulator is dc coupled to the IF port of the mixer, and the output is padded and amplified by U3. The power level at the XMTR_INJ port is similar to the receiver side, close to +17 dBm. The RF feedback is provided by the resistive splitter at the input to Q6. This output is amplified by U2, to a level of approximately 0 dBm. A built-in test (BIT) line is provided that measures the power at the receiver local oscillator injection port. This power is detected in a simple RF power meter that rectifies a sample of the RF and provides a voltage proportional to the LO power. This voltage is used by the A4A1 control card as part of its monitoring of the health of the transceiver. 4.8.5 Receiver Circuit (Refer t o Figure 4-17 and Figure 6-18 , Figure 6-19, Figure 6-22 or Figure 6-23) During the receive mode the antenna signal is applied to the receiver preselector through forward biased T/R diode CR602. The preselector consists of four identical parallel resonant RF filters. Each filter consists of an inductor, a capacitor, and two varactors (voltage variable capacitance diodes). Tuning voltage for the varactors is provided by the A4 synthesizer. The synthesizer incorporates software that determines the optimum tuning voltage for each channel and drives a digital to analog converter (DAC) with this information. The voltage from the DAC is scaled by amplifier U703 on the synthesizer. It varies from +5.0 V dc at 118.000 MHz to +20 V dc at 151.975 MHz. The preselector attenuates undesired signal components to control spurious responses. A variable capacitor and variable inductor in each preselector is used to tune each preselector at high and low frequencies respectively. The output of the preselector is applied to pin-diode attenuator CR209, which is controlled by the RF AGC signal and provides up to 25 dB of attenuation in the presence of strong RF signals. The output of pin-diode attenuator CR209 is applied along with the injection signal from the synthesizer to dual-junction FET mixer Q201 to obtain the first IF signal. The high-side injection frequency varies from 138.025 MHz at receive frequency 118 MHz to 158.025 MHz at receive frequency 138.000 MHz to obtain a first IF frequency of 20.025 MHz. Those transceivers with extended frequency range also use low-side injection (118.000 to 131.950 MHz) to extend the receive frequency up to 151.975 MHz. The output of the first mixer is routed to a switched filter assembly on the A3 power supply/modulator. The logic for determining which filter to select comes from the A4A1 control card. Both filters are 50 ohm crystal filters, with the appropriate 6 and 60 dB bandwidths for 25-kHz and 8.333-kHz channel operation. The output of either FL501 for 25-kHz operation, or FL500 for 8.333-kHz operation, is routed back to the A2 receiver and the input of first IF amplifier Q202. The output of the first IF amplifier is applied to a second IF amplifier before being applied to a second 20.025-MHz filter, FL202. AGC voltages are applied to both Q202 and Q203 for further gain reduction in the presence of strong RF signals. The combined voltage gain of Q202 and Q203 is approximately 25 dB with no AGC signal. Variable capacitors C218, C220, C228, and C230 are used to adjust the 20.025-MHz IF circuits for maximum AGC voltage. The output of the second IF filter is applied to the second mixer, Q204, along with a 1-V, 19.575-MHz injection signal to obtain the 450-kHz second IF signal. The 19.575-MHz low-side injection signal is provided by crystal-controlled local oscillator Q205. The power gain of the mixer is approximately 12 dB. The resultant 450-kHz output of the mixer is amplified by the 2-stage linear IF amplifier U201. U201 provides approximately 80 dB of power gain. AGC is applied to both stages for gain reduction in the presence of strong re-



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theory of operation 523-0771858 ceived signals. The output of IF amplifier U201 is applied to a class-B transistor detector, Q206. Since Q206 is biased on the verge of conduction, it provides both half-wave rectification (detection) and amplification of the audio signal. The output of the detector is applied to the inverting input of IF AGC amplifier U202B, where it is compared with a +6.5-V dc reference. The average dc output of the detector must be less than this reference before the AGC amplifier begins to reduce receiver gain. During normal operation, the amplified RF noise with no input signal is enough to lower the average output voltage of the detector and cause AGC gain reduction to occur. This ample-gain concept ensures that receiver performance remains satisfactory as components age. The output of IF AGC amplifier U202B is applied to both 450-kHz IF amplifiers, the source of both 20.025MHz IF amplifiers, the carrier squelch circuit, and to the inverting input of RF AGC amplifier U202A. The output of the RF AGC amplifier varies from 0 V dc with a strong signal to +8 to +10 V dc with a weak signal, and is applied to pin-diode attenuator CR209 and to gate 2 of both 20.025-MHz IF amplifiers. The application of AGC to both the gate and the source of the 20.025-MHz IF amplifiers extends the attenuation range of each amplifier to approximately 30 dB.



Figure 4-17. VHF-21/22 (C/D) Receiver Circuit, Block Diagram



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theory of operation 523-0771858 4.8.6 Noise Squelch Circuits ( Refer to Figure 4-18 and Figure 6-18 , Figure 6-19, Figure 6-22 or Figure 6-23) The noise squelch circuit consists of audio processing circuitry to operate the squelch switch based on the presence of noise in a frequency band that is out of the range of normal speech frequencies, but dependent on the amount of noise in the IF passband of the receiver. The detected audio from Q206 is sampled by R361 and applied to the high pass filter comprised of U307A, capacitors C319, 320, 321 and resistors R337 and 338. This circuit has a gain peak at approximately 11 kHz; this is high enough in frequency that noise density here is largely independent of the IF bandwidth chosen (FL500 or FL501). The highpass-filtered noise is detected by CR304 and filtered by C323 to obtain a dc voltage proportional to the noise level. The resulting noise is applied to comparator U304A. The voltage reference for the comparator is set by R345 for the 25-kHz channels, and by R336 for the 8.33-kHz channels. This is because of residual differences between channels that appear to arise from individual component differences. The chosen control is switched to U304 pin 3 by single-pole-double-throw (SPDT) FET switch U306, under control of the BW_Select command from the A4A1 control card. This arrangement allows setting the opening point for both modes to be identical. The closing point is determined by hysteresis resistor R341 on U304A, and will vary somewhat between channel modes. The output of the comparator is approximately +12 V dc when the noise signal is less than the noise threshold, and 0 V dc when greater than the threshold. The positive output from the comparator turns on squelch switch U302C in the receiver audio circuit and applies the receiver audio signal to the audio output amplifier. The noise squelch threshold is normally adjusted so that a 3 µV carrier signal will cause audio to be present.



Figure 4-18. VHF-21/22 (C/D) Squelch Circuits, Block Diagram



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theory of operation 523-0771858 4.8.7 Receiver Audio Circuit ( Refer to Figure 4-9 and Figure 6-18 , Figure 6-19, Figure 6-22 or Figure 6-23) Refer to paragraph 4.6.6. 4.8.8 Transmitter Circuit (Re fer to Figure 4-19 and Figure 6-53 thru Figure 6-56) The transmitter is a 4-stage broadband solid-state circuit that amplifies the +20-dBm synthesizer output to an RF output of 16 watts minimum. The first stage, Q601, is a class-A amplifier. Transistors Q602 and Q603 have a small amount of feedback applied and are operating closer to class-AB, while the output amplifier, Q604, is operating class-C. The first two stages are powered by the +16-V dc power supply, while the last two stages are powered by the filtered and protected +27-V dc supply. Both supplies are generated on the A3 power supply/modulator. Output tuning is provided by variable capacitor C650, which is normally adjusted for maximum RF output power at the highest frequency that the transmitter is to be used on. The output is low pass filtered to reject harmonics of the carrier. During the receive mode, T/R switch diodes CR601 and CR602 are forward biased and provide a path for the received signal from the antenna to the receiver preselector. CR601 provides a virtual ground in the lowpass filter to help isolate the antenna from the final stage of transmitter Q604. During the transmit mode, the +16-V dc transmitter power reverse biases CR601 and CR602 to disconnect the antenna from the receiver. Forward and reverse transmit power is sampled through hot-carrier diode detectors CR603 and CR604, connected to transformer T603. The forward and reverse power signals are monitored by the microprocessor to ensure proper operation of the transmitter. The forward power signal is also used to provide the sidetone signal applied to the receiver audio output amplifier. U601 is a temperature-controlled current source that provides the microprocessor with the operating temperature of the RF power amplifier.



Figure 4-19. VHF-21/22 (C/D) Transmitter, Simplified Schematic Diagram



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theory of operation 523-0771858 4.8.9 Modulator Circuit (Refe r to Figure 4-20, Figure 6-28 thru Figure 6-30) The modulator circuitry for the VHF-21/22 (C/D), located on the A3 power supply/modulator, uses low level modulation and a feedback control system to prevent overmodulation of the carrier during audio peaks. Modulation takes place in the VCO assembly, part of the A4 synthesizer CCA, not in the final amplifiers. The feedback circuit functions by comparing the detected envelope of the RF waveform with the modulating audio input, and varying the RF drive to the PA to match the envelope to the audio. The benefits of a modulation control loop are tighter control of modulation to prevent overmodulation, and to prevent excessive distortion as evidenced by AM to FM conversion or spurious components in the transmitted audio spectrum. The incoming audio from the user’s microphone is compressed by an audio compressor consisting of U506, Q500 and Q502. This circuit reduces the peak to average ratio of the audio applied to the modulator, accommodating variation between microphones and voice characteristics. The circuit acts as variable gain amplifier, with the gain set by the feedback path through Q502 and Q500. When the output of U506 exceeds the bias point on Q502, Q502 begins to conduct. This causes Q502 to draw current through R513, which lowers the gate bias on Q500. This reduces the source to drain impedance of Q500, which reduces the signal applied to U506, and therefore the circuit’s output. Potentiometer R505 is provided to compensate for high or low output microphones, and is normally set so that compression begins when the microphone output is at 125 mV rms. The compressed audio signal is applied to switched capacitor lowpass filter U507. U507 is an eighth order elliptic filter which cuts off sharply at 1/100 of the clock frequency. The filter clock is set to 215 kHz for 8.33kHz channels and 816 kHz for 25-kHz channels. The filter clock is generated on the A4A1 control card. U507 provides the audio passband limiting required for the channel width selected. The output of U507 is attenuated through a pair of potentiometers used to set the modulation depth, R503 and R504, selected by switch U511



Figure 4-20. VHF-21/22 (C/D) Modulator Circuit, Block Diagram



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theory of operation 523-0771858 Switched capacitor filters, being sampled structures, need to be post-filtered by a continuous time filter to remove higher frequency aliases in their output. This is accomplished by using a single multiple-feedback (MFB) lowpass filter produced by U506A, capacitors C530 and C534, along with resistors R549, R568, and R570. The -3 dB point on this filter is approximately 17 kHz, or twice the widest bandwidth from U507, but has much less skirt selectivity than U507. U506D, between the filter and the switch U511, is a unity gain buffer to prevent interaction between the LPF and the preceding circuitry. The audio from the LPF, now at the desired peak to peak amplitude and spectrally pure, is applied to U508A through capacitor C537. The output of this amplifier is the desired audio superimposed on a dc level set by carrier power adjust R518. There is a continuous dc path from this point through to the modulator mixer on the VCO assembly. R555 and R515 divide the output of U508A by two. The circuit composed of U508C, R511 (the peak power limit control), diodes CR508A and B, and Q503, acts to reduce the peak swings on the audio by changing the source to drain impedance of Q503. This occurs when peaks of audio from the microphone exceed the voltage sourced by the peak power limit control, changing the bias on the gate of Q503 and shunting signal to ground. In doing so, it also affects the dc level at the junction of R555, R515, and pin 5 of U508B. The signal amplitude is small at this point, to prevent distortion in Q503. U508B is a single pole lowpass filter and amplifier combination, with a cutoff frequency of approximately 16 kHz and a signal gain of 38 (31.7 dB). Before being applied to the error amplifier, positive clipper (U506B, R573) and negative clipper (U508D, R512) are used to restrict the absolute maximum and minimum voltages that the modulating audio-plus-dc signal may reach. The clippers function by providing dc limits on their sides of the high-speed diodes U518 and U500. If the audio exceeds this clamp voltage by a small amount, the diodes conduct and the signal is clamped at the dc level on the respective opamp’s output pin. The forward power signal for the error amplifier is obtained by directional coupler T500, and dc buffered by U509 A&B. The error amplifier consists of high speed op amp U512, the feedback network of R588 and C554, input resistor R595 on the noninverting input, and the combination of R591, R592 on the inverting input. The error amplifier functions by taking the audio on the noninverting input, and subtracting off the detected envelope on the inverting input. The difference between the two is the error in the modulation at that instant. The dynamic characteristics are primarily set by the combination of C554 and R595, with some effects from the C554, R588 combination. C562 and R594 provide balance in the circuit and better performance. There is a time delay between the input audio and the appearance of that audio on the modulated output, but that time delay is small and is accounted for in the design of the control loop. U512 drives Q507, an NPN current buffer, to increase the opamp’s capability for driving the mixer in the VCO assembly A4A1. The reflected power sensed by the directional coupler is used to inhibit the transmit power if reflected power should go too high. This would indicate a defective, damaged, or disconnected antenna. 4.8.10 Power Supply Circuits (R efer to Figure 4-21, Figure 6-28 thru Figure 6-30) Primary dc power for the transceiver is applied through A1 interface circuit card to A3 power supply/modulator circuit card, where it is filtered by L504, C580, and C545 before it is applied to any other circuits. The input filter provides both inductive and capacitive filtering to the primary power. The filtered primary power is applied directly to the switching amplifier in the modulator, the +16-V dc transmitter power supply, and to an overvoltage protection circuit. The overvoltage protection circuits consisting of Q505, Q506, Q501 and VR500 turn off the power supplies when the primary voltage exceeds +36 V dc. During normal operation (less than +36-V dc limit) transistors



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theory of operation 523-0771858 Q506 and Q505 are biased off by the parallel combination of R589 and R590. This allows Darlington transistor Q501 to turn on and provide dc power to the voltage regulators and other circuits in the transceiver. If the primary power exceeds +36 V dc, zener diode VR500 begins to conduct which increases the voltage on the base of Q506, turning it on. This, in turn, increases the current through the combination of resistors R580, R562, R581 and R582, dropping the base voltage on Q505 enough to turn it off, and this turns off Q501. If the voltage produced by the resistive divider on the overvoltage shutdown switch driver U505 exceeds +6V dc, the comparator goes low and turns on switch U503A. This in turn shuts down the transmit lines. The protected +27-V dc supply powers programmable voltage regulator U501, set to deliver a nominal +16 V dc. Diodes CR500 and CR501 protect U501 during the turn off transient. The +16 V dc produced by U501 is used by the A5 transmitter, and is further regulated by +12-V dc regulators U504 and U510, and by +5 V-dc regulator U513. These regulators are self-protecting; in the event of an output short circuit they will foldback current limit rather than be destroyed. They are thermally protected; in the event of thermal overload, they will cycle into a shutdown mode. The +12-V dc regulator drives two switched capacitor voltage inverters, U516 and U517, that produce -5 V dc and -10 V dc respectively. These voltages are used on the modulator. Additional voltage regulation is provided on the A4 synthesizer CCA. Refer to paragraphs 4.8.2 and 4.8.3.



Figure 4-21. VHF-21/22 (C/D) Power Supply Circuit, Block Diagram



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theory of operation 523-0771858 4.8.11 Filter Assembly Circuits (Refer to Figure 4-17, Figure 4-19, Figure 6-58) Filter assembly A8 is used to reduce FM interference caused by high-power FM radio stations. The filter has two sections. The first section consists of A8C101, C102, C103, L101, and L102. These components are connected between the antenna jack, P101-A1 or J102 and A5J611. The second part consists of A8C104 thru C108, L103, and L104. These components are connected from the output of T/R switching diodes A5CR601 and CR602 to the input to the preselector on the A2 receiver card. A8C108 is adjustable to minimize input signals around 102 MHz.



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n523-0771859-208118 8th Edition, 1 October 2001 2nd Revision, 24 May 2002



VHF-21( )/22( ) VHF Comm Transceiver Maintenance Table of Contents Paragraph



Page



5.1 GENERAL ................................................................................................................................................................ 5-1 5.2 TEST EQUIPMENT REQUIRED........................................................................................................................... 5-1 5.2.1 Standard Test Equipment ............................................................................................................................................. 5-1 5.2.2 Special Test Equipment................................................................................................................................................. 5-1 5.3 HANDLING OF UNITS CONTAINING ESDS COMPONENTS ......................................................................... 5-2 5.4 TESTING/ALIGNMENT/TROUBLESHOOTING ................................................................................................. 5-4 5.4.1 Test Setup With ISA Computer .................................................................................................................................... 5-5 5.4.2 Procedures Using Remote Comm Control .................................................................................................................. 5-15 5.4.3 Final Performance (Customer Acceptance) Test ........................................................................................................ 5-16 5.4.4 Adjustment/Alignment Procedures ............................................................................................................................. 5-41 5.4.5 Troubleshooting Tests and Procedures (VHF-21/22(A/B) only)................................................................................. 5-53 5.5 DISASSEMBLY/REPAIR/ASSEMBLY................................................................................................................. 5-75 5.5.1 Disassembly ................................................................................................................................................................. 5-75 5.5.2 Repair ........................................................................................................................................................................... 5-76 5.5.3 Assembly ...................................................................................................................................................................... 5-77 5.5.4 Storage.......................................................................................................................................................................... 5-78 5.6 STRAPPING OPTIONS ........................................................................................................................................ 5-78 5.6.1 VHF-21( ) Audio Compressor Enable.......................................................................................................................... 5-78



NOTICE: This title page replaces eighth edition, first revision title page dated 1 April 2002.



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*The asterisk indicates pages changed, added, or deleted by the current change.



Issue



* Title ......................................... 24 May 02 * List of Effective Pages............. 24 May 02 5-1 thru 5-6................................. 1 Oct 01 * 5-7 thru 5-8.............................. 24 May 02 5-9 thru 5-17 ............................... 1 Oct 01 * 5-18 thru 5-23 .......................... 24 May 02 5-24 thru 5-40 ............................. 1 Oct 01 * 5-41 .......................................... 24 May 02 5-42 thru 5-43 ............................. 1 Oct 01 5-44 ............................................ 1 Aor 02 5-45 thru 5-56 ............................. 1 Oct 01 * 5-57 .......................................... 24 May 02 5-58 thru 5-59 ............................. 1 Oct 01 * 5-60 .......................................... 24 May 02 5-61 thru 5-84 ............................. 1 Oct 01



RETAIN THIS RECORD IN THE FRONT OF THE MANUAL. ON RECEIPT OF REVISIONS, INSERT REVISED PAGES IN THE MANUAL, AND ENTER DATE INSERTED AND INITIALS.



Record of Revisions REV NO



REVISION DATE



1st Ed



INSERTION DATE/BY



SB NUMBER INCLUDED



REV NO



REVISION DATE



10 Jun 83



1



2



24 May 02



2nd Ed



2 Jan 85



1 thru 8



3rd Ed



13 Apr 87



9 thru 13



4th Ed



19 Jul 90



14 thru 20



5th Ed



1 Apr 92



21



6th Ed



11 Aug 93



20R3, 21R1



7th Ed



11 Sep 98



22, 23R1, 24R1, 25, 26, 27



8th Ed



1 Oct 01



28R1, 29, 30R1, 31, 32R1, 33R1, 34R1, 35 thru 41



1



1 Apr 02



INSERTION DATE/BY



SB NUMBER INCLUDED



ROCKWELL COLLINS INSTRUCTION BOOK (REPAIR MANUAL) VHF-21( )/22( ) VHF Comm Transceiver VHF-21( )/22( ) VHF Comm Transceiver INSTRUCTION BOOK (REPAIR MANUAL) (523-0771854, 3RD REVISION, DATED JUL 30/02)



TEMPORARY REVISION NO. 23-12-10-14 Insert facing page List of Effective Pages of the Maintenance Section, 23-12-10 This temporary revision supersedes Temporary Revision 23-12-10-07 Subject: Correct LEP issue. The List of Effective Pages entry for 5-44 should read as follows: 5-44 ...........................1 Apr 02



Temporary Revision 14 523-0771854-3E9113



23-12-10



Page 1 of 5 Mar 6/07



section



V



maintenance 5.1 GENERAL This section provides testing, troubleshooting, alignment, and repair procedures for the VHF-21( )/22( ) VHF Comm Transceiver. These procedures reference instructions that are displayed on the video monitor at the test station. Use the final performance (customer acceptance) test as the first step in fault isolation to locate the functional area of the defective or misaligned circuit. Then perform the troubleshooting or alignment procedures pertaining to that circuit. The troubleshooting procedures provide additional tests and checks to isolate a fault in a functional area. After repair, repeat the final performance (customer acceptance) test to verify proper operation before returning the unit to service. The schematic diagrams in the schematics and illustrated parts lists section and the test point and adjustment location diagrams provided in this section are arranged for convenient viewing when performing the testing, alignment, and troubleshooting procedures. Warning Service personnel are advised to observe standard safety precautions, such as wearing safety glasses, to prevent personal injury while performing maintenance with the covers removed from this unit. 5.2 TEST EQUIPMENT REQ UIRED 5.2.1 Standard Test Equipmen t Table 5–1 lists standard test equipment required for testing, troubleshooting, and alignment of the transceiver. Table 5–2 lists alternate test equipment required for testing, troubleshooting, and alignment of the transceiver Table 5–3 lists the tools required for disassembly/assembly, repair, and alignment. Equivalent equipment may be substituted. 5.2.2 Special Test Equipment Table 5–4 lists the special test equipment required for testing, troubleshooting, and alignment when using an Industry Standard Architecture (ISA) computer. The VHF-21( )/22( ) interface test fixture may be purchased from either JcAIR or ASi at the addresses listed below:



JcAIR, Inc. 400 New Century Parkway New Century, KS 66031 Phone: (913) 764-2452



Revised 1 October 2001



or



JcAir, Inc. P.O. Box 9 New Century, KS 66031-0009



ASi Avionics Specialist, Inc. 3833 Premier Ave. Memphis, TN 38118 Phone: (901) 362-9700



5-1



maintenance 523-0771859 The VHF-21( )/22( ) interface test fixture may also be fabricated locally (refer to Figure 5–25 and Table 5–29). The interconnect cables for connecting the VHF-21( )/22( ) to the interface test fixture are provided with fixtures purchased from JCAir or ASi. The interconnect cables may also be fabricated locally (refer to Figure 5–2 and Figure 5–3). Table 5–5 lists the special test equipment required for the remote comm control method of testing the VHF21( )/22( ) described in paragraph 5.4.2. This method of testing is used for troubleshooting a VHF-21( )/22( ) without a computer. 5.3 HANDLING OF UNITS C ONTAINING ESDS COMPONENTS The VHF-21( )/22( ) contains electrostatic discharge sensitive (ESDS) components that can be damaged by static voltages present in most repair facilities. Although most ESDS components contain internal gate protection circuits, good practice dictates careful handling of all ESDS components. Table 5–1. Standard Test Equipment Required. EQUIPMENT



MANUFACTURER



CHARACTERISTIC



FUNCTION



Dc power source



HP-6267B-005



0 to +30 V dc, 0 to 10 A



Supply input power



RF signal generator



HP-8654B, HP-8640B*, or IFR-NAV-750B



100 to 170 MHz ±1%, 0 to 95% modulation, 0- to 1-V output*, 50-Ω input impedance



RF signal source



Marconi/IFR 2040, 2023, or HP-8657B† RF amplifier*



Q-bit model QB-300 (bnc)** or Mini Circuits model ZHL-6Abnc***



+20 dB RF gain in 100- to 170MHz range, max input drive greater than or equal to 1 V rms.



Provides +20 dB or greater RF gain



Audio signal generator



HP-467A/HP-200CD or HP-3311A



20 Hz to 40 kHz ±2%, 1W into 600 Ω



Audio signal source



Frequency counter



HP-5245L with HP-5253B converter or HP-5345A



100 to 170 MHz ±1 digit



Frequency measurements



Oscilloscope



Tektronix 465, 475, 2235, or 2335



Dc to 80 MHz



Modulation envelope and waveforms



Dvm



Fluke 8040A/8010 with A90 current shunt set



100 mV to 50 V dc ±1 digit, 0 to 10 A ±2%



Dc measurements



Ac voltmeter



HP-400D/E



1.0 mV to 10 V rms ±2% of fullscale, 10 Hz to 20 kHz



Audio output measurements



RF voltmeter



Boonton 92C with 52-ohm probe



1 to 500 mV ±5%, 100 to 170 MHz



RF voltage measurements



RF wattmeter



Bird Thruline 50C or Bird 612



50 W, 115 to 170 MHz



RF power measurements



RF load



Bird Termaline 81B



50 Ω, 50 W, 115 to 170 MHz



RF load



6-dB pad



Weinschel 1A-6



50 Ω



Impedance matching



1W, 600 Ω, ±1.5 dB



Signal-to-noise measurements



Audio power meter or Sinadder



Helper Inst Co. Model S-103



RF power attenuator RF fuseholder



* ** *** †



HP-11509A



20 mV to 10 V rms, ±1 dB 50 Ω, 50 W, 40 dB



RF measurements



Frequency range: 30 to 156 MHz Loss ≤ 1 dB Swr ≤ 1:35



Protection of RF generator if radio accidentally transmits



RF amplifier is required when using an HP-8640B or IFR-NAV-750B to meet the required 1-V rms output. Q-bit Corp., 2575 Pacific Ave., Palm Bay, FL 32905, Phone (407) 727-1838 Mini Circuits, P.O. Box 350166, Brooklyn, NY 11235, Phone (800) 523-8451 Low-noise generator (or equivalent) required for testing 8.33 kHz channel selectivity on C/D units.



Revised 1 October 2001



5-2



maintenance 523-0771859 Table 5–2. Alternate Test Equipment. EQUIPMENT Digital modulation analyzer



MANUFACTURER



CHARACTERISTIC



HP-8901 or equivalent



150 kHz to 1300 MHz



FUNCTION Provides an alternate method from using an oscilloscope to analyze modulation envelope and waveforms



Table 5–3. Tools Required. DESCRIPTION



CHARACTERISTIC



FUNCTION



20-W soldering iron



Any with grounded tip



Remove/replace ICs and components



Solder sucker



Any



Remove solder



Needle-nose pliers



Any



Bend component leads



Cutting tools



Various, small diagonal cutter, end nippers, etc (sharp tools that do not leave burrs)



Cut IC and component leads



Adjustment tools



JFD 5284 or equivalent



Adjust various resistors and capacitors



Plastic hex



Adjust various coils



Various Phillips



Disassembly/reassembly



Standard



Dust cover removal/replacement



Screwdrivers



Table 5–4. Special Test Equipment Required With ISA Computer. EQUIPMENT VHF-21( )/22( ) Interface Test Fixture



DESCRIPTION Available in three options: 1.



Fabricate as shown in Figure 5–25 and Table 5–29.



2.



JcAIR Model 22H-1A



3.



Avionics Specialists ASI-200-3 test module for use in the ASI-2000 test system



VHF-21( ) Interconnect Cable



Fabricate as shown in Figure 5–2. (Cable supplied with JcAIR Model 22H-1A and ASI-200-3 test module.)



VHF-22( ) Interconnect Cable



Fabricate as shown in Figure 5–3. (Cable supplied with JcAIR Model 22H-1A and ASI-200-3 test module.)



Computer (Minimum Requirements)



ISA-bus (AT Compatible), 8 MHz 286 CPU, 640 KB ram, 40-MB hard drive, 3-1/2inch (1.44 MB) floppy drive, VGA video, 1 parallel port, 3 empty full-size ISA expansion slots Microsoft DOS version 3.3



Computer (Recommended Requirements)



VESA local bus computer, 66 MHz 486DX2 CPU, 1 MB ram (expandable to 16 MB), 200 MB hard drive, 3-1/2-inch (1.44 MB) floppy drive, SVGA video, 1 parallel port, 1 serial port, 5 empty full-size ISA expansion slots Microsoft DOS version 6.2 (or newer)



ASCII Printer (optional) Cable, printer



Epson FX-870, HP LaserJet or compatible (80 characters wide, 60 lines per page) Standard Centronics-type parallel printer cable



Collins CTC-429 CSDB/ARINC Interface Test Card



CPN 822-0854-001; used for CSDB, ARINC 429, and digital I/O interface



*Pro Line II/PC Interface Panel and Cables (7 required)



Made by JcAIR and Avionics Specialists, Inc (ASi). The JcAIR model number for the Pro Line II PC Interface Panel is PLPC2000 (part no 01-0684-00); the ASi model number is ASI-401.



Revised 1 October 2001



5-3



maintenance 523-0771859 Table 5–4. Special Test Equipment Required With ISA Computer. EQUIPMENT



DESCRIPTION Cables:



Test Software for ISA Computer



W2 W3 W7 W8 W10 W12 W14



DISCRETE INPUTS DISCRETE OUTPUTS CSDB/CABLE ID ARINC 429 ARINC 429/CSDB CTC-429 DISCRETE I/O CTC-429 DISCRETE I/O



CPN 523-0777-552, VHF-21( )/22( ) Test Disk. Note No calibration of the special test equipment is required.



Table 5–5. Special Test Equipment Required For Remote Comm Control Testing. EQUIPMENT



DESCRIPTION



VHF-22( )/Comm Control Test Set



Fabricate as shown in Figure 5–10 and Table 5–6.



VHF-22( )/CTL-20/Comm Control Test Set, Interconnect Cable



Fabricate as shown in Figure 5–8.



VHF-22( )/CTL-22/Comm Control Test Set, Interconnect Cable



Fabricate as shown in Figure 5–9



VHF-20/20A/20B Test Panel



Fabricate as shown in Figure 5–6. (Refer to the VHF-20A/20B VHF Transceiver instruction book for additional information.) Note No calibration of the special test equipment is required.



The following precautions should be observed when handling all ESDS components and units containing ESDS components. a. Deenergize or disconnect all power and signal sources and loads used with unit. b. Place the unit on a grounded, conductive work surface. c. Ground the repair operator through a conductive wrist strap or other device using a 1-MΩ series resistor to protect the operator. d. Ground any tools (including soldering equipment) that will contact the unit. Contact with the operator’s hand provides a sufficient ground for tools that are otherwise electrically isolated. e. All ESDS replacement components are shipped in conductive foam or tubes and must be stored in the original shipping container until installed. f. When ESDS devices and assemblies are removed from the unit, they should be placed on the conductive work surface or in conductive containers. g. When not being worked on, wrap disconnected circuit boards in aluminum foil or in plastic bags that have been coated or impregnated with a conductive material. h. Do not handle ESDS devices unnecessarily or remove them from their packages until actually used or tested. Failure to observe all of these precautions can cause permanent damage to the ESDS device. This damage can cause the device to fail immediately or at a later date when exposed to an adverse environment. 5.4 TESTING/ALIGNMENT/ TROUBLESHOOTING Two methods for testing, aligning, and troubleshooting the VHF-21 ( )/22( ) are provided in this section. The first method uses a data bus simulator consisting of an Industry Standard Architecture (ISA) computer to test the radio. Step-by-step procedures are displayed along with the desired results. A printer option allows the technician to retain a hard copy of the test results for reference/file use. The test programs are written to provide explicit operator instructions and to allow a variety of monitoring/troubleshooting approaches. Some



Revised 1 October 2001



5-4



maintenance 523-0771859 selected test operations are automatically performed by the software to lower test time and enhance technician efficiency. The second method of testing requires a remote comm control. Step-by-step procedures are given in paragraph 5.4.2. This test method allows an alternate test station to be built and is intended to be used for troubleshooting purposes only. The final performance (customer acceptance) test listed in Table 5–15 must be performed using the data bus simulator method of testing before returning a repaired VHF-21( )/22( ) to service. Both test methods assume that the technician is familiar with the use of the test equipment. 5.4.1 Test Setup With ISA Com puter 5.4.1.1 ISA Computer Setup Refer to the CTC-429 CSDB/ARINC Interface Test Card repair manual (CPN 523-0777510) for setup information on the ISA Computer. 5.4.1.2 Test Setup Connect the test setup as shown in Figure 5–1. Connect the dc power source to the Pro Line II/PC interface panel but do not apply power until instructed to do so in the test program. Connect the transceiver to be tested to the test setup. If using a fabricated interface test fixture, use the interconnect cable illustrated in Figure 5–2 for the VHF-21( ) or the one illustrated in Figure 5–3 for the VHF-22( ). 5.4.1.3 ISA Computer Test Prog ram Loading Insert the floppy disk into the appropriate disk drive on the ISA computer. Type in the floppy drive followed by “INSTALL”, example A:\INSTALL, and press ENTER. The install program loads the VHF-21( )/22( ) test program files onto the computer’s hard drive in the \COLLINS\VHF-21_22 directory. When completed, the VHF-21( )/22( ) VHF Comm Test Program appears in the Collins Program Menu. If the installation of the test program is the first Collins program on the computer, the program will require installation of the Collins Program Menu. Follow the instructions given by the program on the screen. The program lists the drives available. Select the drive to install the software on. The program then copies the files to run the menu and the VHF-21( )/22( ) test program on the appropriate directories. The menu program files are in the \COLLINS directory and the VHF-21( )/22( ) program files are in the \COLLINS/VHF21_22 directory. The AUTOEXEC.BAT and CONFIG.SYS files on the computer are then inspected and if changes are required, three options are displayed. The files can be modified, example files can be made to show what the changes would be, or the installation program can be aborted and no changes made. Following the installation, the computer should be rebooted (CTRL-ALT-DELETE) to permit the AUTOEXEC.BAT and CONFIG.SYS changes to take effect. Refer to your DOS reference manual for additional information on AUTOEXEC.BAT and CONFIG.SYS files.



Revised 1 October 2001



5-5



maintenance 523-0771859



Figure 5–1. Data Bus Simulator With ISA Computer, Test Setup



Revised 1 October 2001



5-6



maintenance 523-0771859



Figure 5–2. VHF-21( ) Interconnect Cable



Revised 24 May 2002



5-7



maintenance 523-0771859



Figure 5–3. VHF-22( ) Interconnect Cable



Revised 24 May 2002



5-8



maintenance 523-0771859 5.4.1.4 Operation of Collins Pro gram Menu To run the Collins Program Menu from the DOS prompt, type in “Collins” and press ENTER. The screen displays the current test programs loaded on the computer’s hard drive. Highlight the VHF-21( )/22( ) test program then press ENTER to start the program. 5.4.1.5 ISA Test Program Overv iew The test programs for the VHF-21( )/22( ) are loaded onto the computer hard drive when using an ISA computer. The test programs are designed to be self-reading and provide prompts when user input is required. The MAIN TEST MENU is shown below: MAIN TEST MENU 1. 2. 3. 4. 5. 6. 7.



UUT Identification Final Performance Test Final Performance Test Printer Alignment Comm Control Self-Test Internal Monitoring



Your choice: Press ESC to exit The paragraphs that follow provide a detailed description of each item from the MAIN TEST MENU. 5.4.1.5.1 UUT Identification (Init ialization) On initial testing of unit, select menu item 1, UUT Identification, to input the part number of the unit, serial number, and installed service bulletins. The data entered allows the program to use the particular tests appropriate for the UUT (unit under test).



Revised 1 October 2001



5-9



maintenance 523-0771859 5.4.1.5.2 Final Performance Test After initialization, select Final Performance Test from the MAIN TEST MENU. A menu is displayed which allows three different methods of running the Final Performance Test: Select one of the following test methods 1. manual testing 2. semiautomatic testing 3. semiautomatic testing until a test fails Your choice: Select menu item 1, 2, or 3 to start the final performance test in the desired mode. In the manual test mode, press ENTER after the test program displays “TEST:PASSED”, “TEST:FAILED”, or “NO DATA ENTERED” on the screen. In the semiautomatic test mode, the next test step starts automatically after the current test displays “TEST:PASSED”, “TEST:FAILED”, or “NO DATA ENTERED”. In semiautomatic testing until a test fails mode, testing is similar to semiautomatic testing except testing stops on any test that fails. Pressing the escape key when viewing the MAIN TEST MENU screen makes the program return to the initial screen. Pressing the escape key when viewing the select test method screen makes the program return to the MAIN TEST MENU. After selecting the desired testing method, the next screen describes how to control the movement through the test. This screen is followed by the pretest instructions. The program then initializes the UUT. During the initialization, the program checks for test cable ID and verifies CSDB data from the UUT. The program then proceeds to the final performance test. The data bus simulator displays the test number of the current test step. If the data bus simulator escape key is pressed while the final performance test is in operation, the current test is interrupted and the following test control information appears at the bottom of the screen. TEST: PASSED or FAILED or NOT TESTED RETURN=CONT ESC=MENU P=PREV R=REPEAT Press ENTER to continue operation, press escape to show the TEST CONTROL MENU, press P to run the previous test, or press R to repeat the current test. Press the data bus simulator escape key only if there is a need to interrupt the unit tests or to quit the unit test procedure. The TEST CONTROL MENU is given below. TEST CONTROL MENU 1. 2. 3. 4. 5.



Run current test Run previous test Run next test Select test mode Select top-level test



Press ESC to exit



Revised 1 October 2001



5-10



maintenance 523-0771859 The TEST CONTROL MENU lets the test operator start the test procedure at the test step when escape was pressed (selection 1), run the previous test (selection 2), run the next test (selection 3), select the test method you would like, manual, semiautomatic, or semiautomatic until a test fails (selection 4), or show the top-level test menu (selection 5). No data is lost if escape is pressed while the test program is in operation. However, all test results are lost if the TEST CONTROL MENU is shown and escape is pressed again to go to the MAIN TEST MENU. Pressing 5 to go to the top-level test menu makes the program display a list of VHF-21( )/22( ) final performance tests in test order. The test names on the TOP LEVEL TESTS MENU might not be the same as the test names given in the test descriptions table but the test numbers match. You can run any test on the TOP LEVEL TESTS MENU by keying in the test number and then pressing the ENTER key. The TOP LEVEL TESTS MENU is as follows: TOP LEVEL TESTS 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.



CSDB DIFFERENTIAL OUTPUT CSDB (SERIAL) CONTROL PARALLEL (2 X 5) CONTROL RECEIVER SENSITIVITY RECEIVER RESIDUAL OUTPUT/QUIETING SIMULCOMM LEVEL RECEIVER AGC RECEIVER AUDIO RECEIVER AUDIO COMPRESSOR RECEIVER AUDIO FREQ RESPONSE RECEIVER SELCAL RECEIVER SQUELCH RECEIVER SELECTIVITY TRANSMITTER OUTPUT TRANSMITTER MODULATION TRANSMITTER AUDIO LEVELS TRANSMITTER FREQUENCY



5.4.1.5.3 Final Performance Test Printer Program Item 3 on the MAIN TEST MENU, Final Performance Test Printer, is a printer program that prints a hard copy of the final performance test results, provided the test results were saved prior to exiting the final performance test program described in paragraph 5.4.3. The following menu is displayed when the printer program is selected. PRINTER SELECT MENU 1. Print test results 2. Display test results on monitor 3. Change header name Your choice: Press ESC to exit Select item 1 to display printer setup instructions and to print a hard copy of the test results. Select item 2 to view the test results before printing. Select item 3 to modify the name printed on the header of the first page of the hard copy. Press the escape key to return to the MAIN TEST MENU.



Revised 1 October 2001



5-11



maintenance 523-0771859 5.4.1.5.4 Alignment Procedure Prog ram The alignment program provides a step-by-step procedure for the transceiver during which the computer automatically tunes the transceiver to the desired frequency and selects any pertinent discretes for each test. Select item 4, Alignment, from the MAIN TEST MENU and instructions are displayed to control movement through the test. The program then initializes the UUT. During the initialization, the program checks for test cable ID and verifies CSDB data from the UUT. The program then proceeds to the alignment procedure. The alignment program displays the computer tuning frequency in the upper left corner of the monitor screen and the frequency returned by the transceiver in the upper right corner. In most alignment steps the two frequencies should be the same. This indicates correct transceiver tuning. If a frequency response is not received from the transceiver, a “NO DATA” message is displayed. This indicates that the transceiver is not transmitting data and the procedure cannot be completed with the desired results. A text version of the alignment procedures is provided in Table 5–16. Pressing the escape key when “ESC=MENU” is displayed at the bottom of the screen will cause the control menu to be displayed: CONTROL MENU 1. 2. 3. 4. 5.



Run current step Run previous step Run next step Select test mode Select Top-Level Test



Your choice: Press ESC to exit Selecting option 5 makes the program display a list of alignment steps which may be individually selected: ALIGNMENT STEPS 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.



Initial Setup Power Supply Synthesizer Alignment Filter Alignment Receiver Alignment Receiver AGC Adjustment Receiver Squelch Audio Output Level Adjustment Transfer Tone Level Simulcomm Test Select Transmitter Microphone Gain Transmitter RF Output Modulation Depth Adjustment Sidetone Adjustment Frequency Standard Adjustment End of Alignment



Your choice: Press ESC to exit



Revised 1 October 2001



5-12



maintenance 523-0771859 5.4.1.5.5 Comm Control Program The comm control program provides a versatile means of exercising the VHF-21( )/22( ). When first selected from the MAIN TEST MENU, this program performs a self-test on the transceiver to verify its status and to identify any faults that are found. Figure 5–4 shows the screen display that would appear immediately after the self-test when a fully operational VHF-22B is connected to the test fixture. The lighty-shaded items on the screen display can be either modified or selected by the operator to fully exercise and examine the transceiver. These items are selected by either pressing the space bar or by typing the first letter of the desired item (T for TEST, F for FREQ, etc). Reverse text is used to identify the item to edit or toggle. To edit an item, press the ENTER key and enter the desired frequency or number. To toggle an item, press the ENTER key and the item will change to the next mode. An example would be to change the TUNE MODE: from CSDB by pressing ENTER to toggle the TUNE MODE: to 2 × 5. Pressing ENTER again returns the TUNE MODE: back to CSDB.



Figure 5–4. Control Program Display Screen, CSDB Tune Mode



The COMM CONTROL screen is divided into the following four sections. The top section is the DIAG CODES and input/output discretes used by the VHF-21( )/22( ). When DIAG CODE is highlighted, press ENTER to view one of the diagnostic codes output from the VHF-21( )/22( ). The COMM CONTROL screen allows the user to be able to toggle the input discretes to the VHF-21( )/22( ) and verify the changes in the CSDB output from the VHF-21( )/22( ). The following paragraphs list the discretes operation.



Revised 1 October 2001



5-13



maintenance 523-0771859 SQUELCH: This discrete can be toggled between DSBL (disabled) and ENBL (enabled). When squelch is enabled (provided the CSDB WORD 10 SQCH: bit is set to enable), the audio output is squelched until a signal is applied. When squelch is disabled, the audio output noise is always present. SIMULCOM: (VHF-22( ) only) This discrete can be toggled between ON and OFF. When simulcom is on, the receiver sensitivity is decreased from 3 to 10 µV. Simulcom is used to lower the sensitivity of the receiver when another comm is transmitting. TUNE MODE: This discrete allows selection of either CSDB or 2 × 5 mode. TUNE MODE changes the strap on the VHF-21( )/22( ) that selects the serial (CSDB) or parallel (2 × 5) mode. CSDB OUT discrete is automatically set to ON for CSDB mode and OFF for 2 × 5 mode. CSDB OUT changes with TUNE MODE to provide a normal operating environment default. However, if a different configuration is desired, simply select CSDB OUT after setting TUNE MODE. With TUNE MODE in the 2 × 5 mode, the FREQ discrete (in the next section) is used to change the 2 × 5 frequency information sent to the VHF-21( )/22( ). CSDB OUT: See TUNE MODE. CARRIER SQ: This is an output from the VHF-21( )/22( ) indicating the current status of the carrier squelch circuit, LO or HI. RXCOMPR: This discrete is toggled between OFF and ON. When ON the receiver compressor circuit helps smooth out the variation in speech levels between various received signals. UID: The unit identifier discrete is toggled between COMM 1, COMM 2, COMM 3, and 0. Note Changing the CSBD UID input discretes to the transceiver may cause invalid conditions and/or loss of communication between the computer and the transceiver. Note In the VHF-21( )/22( ) interface test fixture, the 0.01-MHz and UID lines are the same pins on the rear connector. This is necessary for testing the VHF-21( ). In an aircraft installation this does not cause a problem, since either CSDB or 2 × 5 mode is selected at the time of installation and is not changed in normal operation. However, this program allows switching between CSDB and 2 × 5 modes. To compensate for this, the UID or last 2 bits of the 2 × 5 frequency are stored as that information goes off the computer display. When they return to the screen, the previous value is restored. Another similar condition exists on the VHF-21( ), where the 10-MHz pins also are used to select TUNE MODE. In this case, memory is used only when testing a VHF-21( ). 2 × 5 10-MHz information is stored when in CSDB mode and restored in 2 × 5 mode. The next section is the CSDB DATA WORD (hex 10 or 12). This word is also referred to as the CSDB COMM FREQUENCY INPUT WORD. The data in this section is sent from the computer to the VHF-21( )/22( ) at all times (except when CSDB OUT is set to OFF). Frequency, ID, self-test, squelch, and transfer control can be modified by changing the appropriate entry. This section also allows modification of each bit in bytes 1 through 5 of the frequency word (modification of byte 0 is not allowed, as it is the label). Refer to Table 5–7 or Table 5–8 for a more detailed description of the CSDB comm frequency input words. Table 5–11 shows the correspondence between actual operating frequency, channel name, CSDB label transmitted to the transceiver, and CSDB word content.



Revised 1 October 2001



5-14



maintenance 523-0771859 Note In the CSDB DATA WORD section, the user may modify frequency data in the FREQ field. This data entry must be the desired operating frequency and NOT the channel name. Refer to Table 5–11 to cross reference operating frequency with channel name. Note The CSDB control screen now includes the data word labels 10 and 12, as well as the bench word label F1 (refer to Table 5–14). The user may select any label by positioning the cursor over the label and pressing ENTER. Once selected, transmission of the label to the UUT can be turned on or off. By positioning the cursor on the field to the right of each label and pressing ENTER, the user can toggle between OFF or XMT, turning transmission of the label to the UUT off or on, respectively. By using this method, all, none, or any combination of the 3 labels can be transmitted to the UUT. Be sure to turn on only the label to be transmitted. For example, when transmitting label 12 (8.33 kHz), turn off label 10 (25 kHz) and label F1 for proper operation. If labels 10 and 12 are both being transmitted to the UUT, label 10 has priority. Turn off labels 10 and 12 if transmitting the bench word label F1. Labels 10, 12, and F1 will be available when testing 8.33 kHz units, while only labels 10 and F1 will be available while testing 25 kHz units.



The third section is identified by COMM FREQ WORD (hex 11 or 13). This word is also referred to as the CSDB COMM DATA OUTPUT WORD. The data in this section is sent from the VHF-21( )/22( ) to the computer at all times. This section indicates if the VHF-21( )/22( ) is running a self-test or transmitting. Also indicated is the frequency to which the VHF-21( )/22( ) is tuned, the ID of the word being received by the computer, and the maximum tunable frequency. Adjacent to COMM FREQ WORD are hex bytes 1 through 5 of the data word. Refer to Table 5–9 or Table 5–10 for a detailed description of the CSDB comm frequency output words. Table 5–12 shows the correspondence between actual operating frequency, channel name, CSDB label transmitted by the transceiver, and CSDB word content. The fourth section is identified by CSDB DIAG WORD (hex F3). The data in this word is sent from the VHF21( )/22( ) to the computer. The highest priority diagnostic code being sent from the VHF-21( )/22( ) is displayed in this section along with a description of the code meaning. Adjacent to CSDB DIAG WORD (F3) are hex bytes 1 through 5 of the diagnostic word; refer to Table 5–13 for a detailed description of the CSDB diagnostic output word. 5.4.1.5.6 Self-Test Diagnostics Pr ogram Item 4 on the MAIN TEST MENU provides a CSDB independent self-test program on the transceiver. The self-test describes any diagnostic codes that are returned by the transceiver after the test. The CSDB selftest can also be initiated during the control program. 5.4.1.5.7 Internal Monitoring Pro gram The internal monitoring program, MAIN TEST MENU item 5, provides a convenient means for examining the analog values that can be measured with the CSDB bench test word (label F1) described in Table 5–14. Selected values are displayed on the screen along with any other pertinent data, such as the normal operating limits.



Revised 1 October 2001



5-15



maintenance 523-0771859 5.4.2 Procedures Using Remot e Comm Control Instead of automatic tuning by a data bus simulator, a remote comm control can be used to tune the VHF-21( )/22( ) to the desired frequency. In each step where applicable, the final performance test specifies when the data bus simulator tunes the VHF-21( )/22( ). When using a remote comm control, manually channel the comm control to the specified frequency. Note The remote comm control method of testing is intended to be used for troubleshooting purposes only and will not perform all of the final performance tests listed in Table 5–15. This method cannot be used to test VHF-21/22(C/D) units in 8.33-kHz tuning mode. A repaired VHF-21( )/22( ) is required to pass all final performance tests using a data bus simulator before it is returned to service. 5.4.2.1 Test Setup 5.4.2.1.1 VHF-21A/21B Ensure that the VHF-20/20A/20B test panel power is turned off and connect the transceiver to be tested to the test setup illustrated in Figure 5–5. Use the VHF-21( ) interconnect cable illustrated in Figure 5–2. Use a 313N-( ) Comm Control when parallel data transfer must be verified. To verify serial data transfer and to utilize the self-test capabilities of the transceiver, use a CTL-22 Comm Control. The VHF-20/20A/20B test panel schematic diagram is shown in Figure 5–6. 5.4.2.1.2 VHF-22A/22B Ensure that test set power is turned off and connect the transceiver to be tested to the test setup illustrated in Figure 5–7. Use a CTL-20 Comm Control and the interconnect cable shown in Figure 5–8 when parallel data transfer must be verified. To verify serial data transfer and to utilize the self-test capabilities of the transceiver, use a CTL-22 Comm Control and the interconnect cable shown in Figure 5–9. Refer to Figure 5–10 and Table 5–6 for the VHF-22( )/comm control test set schematic diagram and parts list. 5.4.3 Final Performance (Cus tomer Acceptance) Test The final performance test program provides a step-by-step test of the transceiver. A description of each final performance test is provided in Table 5–15 using an ISA computer. The final performance test program uses the computer to automatically tune the transceiver to the desired frequency and select any pertinent discretes for each test. The final performance test can be performed as a customer acceptance test. The final performance test must be performed after repairs have been made and/or whenever the unit dust cover has been removed. The final performance tests can also be used to isolate a fault to a functional area, thus determining which troubleshooting or adjustment procedures are applicable. Some of the performance criteria have been adjusted to allow for the tolerances of typical test equipment. The final performance test should be run in sequence for a proper final test of the transceiver and to ensure that the results are stored properly for printout later. Caution A 50-ohm coaxial in-line fuse is recommended for additional generator protection against accidental transmitter keying. Up to a 1-dB loss may result, which should be accounted for if the measurement is marginal.



Revised 1 October 2001



5-16



maintenance 523-0771859 Note All specified RF signal generator output levels are hard microvolts. These are the levels marked on the attenuators of most signal generators, provided that a 6-dB pad is connected between the signal generator and the transceiver antenna connector. If a Collins 479S-6A VOR/ILS Signal Generator is used, set it up to indicate signal levels in microvolts and do not use an external 6-dB pad. If a 6-dB pad is not available to use with most other generators, less accurate but generally useful results can be obtained by dividing all RF levels by two. Use of the pad is recommended, both to provide consistent and repeatable results and to provide some protection for the generator if the transmitter is accidentally keyed. When the final performance test is run, the bottom of the monitor displays serial data output (WORD 11 from VHF) and the status of the discretes. This data can be used to verify the unit is responding properly to the test. Connect the transceiver to be tested to the appropriate test setup (refer to paragraph 5.4.1). Ensure that all test set switches are set at the down position. Apply +27.5 ±0.5-V dc power to the test setup and turn on the comm control. If a permanent record of the final performance test results is required, they can be stored at the end of each test. Upon completion of the final performance test, the stored test results must be saved to the disk before they can be sent to the printer by the printer program. The procedure for transferring the test results is displayed on the monitor when the transfer must be performed. Failure to transfer the test results before exiting the final performance test will result in the loss of the test results. Once the test results have been transferred to the disk, the results can be printed on the printer either immediately or at a later time. Note, however, that only one set of test results can be stored on the disk at a time.



Revised 1 October 2001



5-17



maintenance 523-0771859



Figure 5–5. VHF-21( ) Test Setup Using Remote Comm Control



Revised 24 May 2002



5-18



maintenance 523-0771859



Figure 5–6. VHF-20/20A/20B Test Panel, Schematic Diagram



Revised 24 May 2002



5-19



maintenance 523-0771859



Figure 5–7. VHF-22( ) Test Setup Using Remote Comm Control



Revised 24 May 2002



5-20



maintenance 523-0771859



Figure 5–8. VHF-22( )/CTL-20 Comm Control Test Set, Interconnect Cable



Revised 24 May 2002



5-21



maintenance 523-0771859



Figure 5–9. VHF-22( )/CTL-22 Comm Control Test Set, Interconnect Cable



Revised 24 May 2002



5-22



maintenance 523-0771859 Table 5–6. VHF-22( )/Comm Control Test Set, Parts List. SYMBOL



COMPONENT DESCRIPTION



COLLINS PART NUMBER



C1



Capacitor, 100µF, 50V



184-5102-010



F1



Fuse, 7A slow-blow, 125V



264-0221-000



Fuseholder



265-1171-000



J1



Connector, 37-pin



371-0171-000



J2



Binding post, double



372-2240-010



J3, J5, J7, J9, J11, J13



Jack, tip, black



360-0151-000



J4, J6, J8, J10, J12, J14



Jack, tip, red



360-0150-000



S1



Switch, 1pdt, toggle



266-3068-000



S2, S3, S4



Switch, 1pdt, miniature toggle



266-5321-150



Figure 5–10. VHF-22( ) Comm Control Test Set, Schematic Diagram



Revised 24 May 2002



5-23



maintenance 523-0771859 Table 5–7. CSDB Comm Frequency Input Word — Hex 10. BYTE



BIT



0



1 2 3 4 5 6 7 8



Label = 0 (LSB) Label = 0 Label = 0 Label = 0 Label = 1 Label = 0 Label = 0 Label = 0 (MSB)



1



9 10 11 12 13 14 15 16



*Unit ID *Unit ID Self-test = 1 Active/preset Squelch (1 = disabled) XFR tone Pad = 0 Freq valid = 1



17 18 19 20 21 22 23 24



2



3



4



5



DEFINITION



CSDB CONTROL PROGRAM DISPLAY OF BYTES 1 THROUGH 5



FREQ VALID =1



PAD



XFR TONE =1



SQ DSBL =1



PRESET =1



SELFTEST =1



UNIT ID



UNIT ID



16



15



14



13



12



11



10



9



Pad = 0 Pad = 0 Pad = 0 Pad = 0 0.001 MHz 0.002 MHz 0.004 MHz 0.008 MHz



0.008 MHz



0.004 MHz



0.002 MHz



0.001 MHz



PAD



PAD



PAD



PAD



24



23



22



21



20



19



18



17



25 26 27 28 29 30 31 32



0.01 MHz 0.02 MHz 0.04 MHz 0.08 MHz 0.1 MHz 0.2 MHz 0.4 MHz 0.8 MHz



0.8 MHz



0.4 MHz



0.2 MHz



0.1 MHz



0.08 MHz



0.04 MHz



0.02 MHz



0.01 MHz



32



31



30



29



28



27



26



25



33 34 35 36 37 38 39 40



1 MHz 2 MHz 4 MHz 8 MHz 10 MHz 20 MHz 40 MHz Pad = 0



PAD



40 MHz



20 MHz



10 MHz



8 MHz



4 MHz



2 MHz



1 MHz



40



39



38



37



36



35



34



33



41 43 44 45 46 47 48



Pad = 0 Pad = 0 Pad = 0 Pad = 0 Pad = 0 Pad = 0 Pad = 0



PAD



PAD



PAD



PAD



PAD



PAD



PAD



PAD



48



47



46



45



44



43



42



41



*Unit ID (identifier) bits are defined below: BIT 10



BIT 9



UNIT ID



VHF-21( ) UID STRAPS



VHF-22( ) UID STRAPS



0 0 1 1



0 1 0 1



All units 1 2 3



P1-19/20 gnd P1-19/20 open P1-19 open/P1-20 gnd P1-19 gnd/P1-20 open



P1-27/28 open P1-27 open/P1-28 gnd P1-27 gnd/P1-28 open



The VHF-21( )/22( ) will not accept tune information if the unit ID does not match the unit ID straps. UID straps on the VHF-21( ) are P1-19 and P1-20; on the VHF-22( ), they are P1-27 and P1-28.



Revised 1 October 2001



5-24



maintenance 523-0771859 Table 5–8. CSDB Comm Frequency Input Word (8.33-kHz Channels) — Hex 12. BYTE



BIT



0



1 2 3 4 5 6 7 8



Label = 0 (LSB) Label = 1 Label = 0 Label = 0 Label = 1 Label = 0 Label = 0 Label = 0 (MSB)



1



9 10 11 12 13 14 15 16



*Unit ID *Unit ID Self-test = 1 Active/preset Squelch (1 = disabled) XFR tone Pad = 0 Freq valid = 1



17 18 19 20 21 22 23 24



2



3



4



5



DEFINITION



CSDB CONTROL PROGRAM DISPLAY OF BYTES 1 THROUGH 5



FREQ VALID =1



PAD



XFR TONE =1



SQ DSBL =1



PRESET =1



SELFTEST =1



UNIT ID



UNIT ID



16



15



14



13



12



11



10



9



Pad = 0 Pad = 0 Pad = 0 Pad = 0 0.001 MHz 0.002 MHz 0.004 MHz 0.008 MHz



0.008 MHz



0.004 MHz



0.002 MHz



0.001 MHz



PAD



PAD



PAD



PAD



24



23



22



21



20



19



18



17



25 26 27 28 29 30 31 32



0.01 MHz 0.02 MHz 0.04 MHz 0.08 MHz 0.1 MHz 0.2 MHz 0.4 MHz 0.8 MHz



0.8 MHz



0.4 MHz



0.2 MHz



0.1 MHz



0.08 MHz



0.04 MHz



0.02 MHz



0.01 MHz



32



31



30



29



28



27



26



25



33 34 35 36 37 38 39 40



1 MHz 2 MHz 4 MHz 8 MHz 10 MHz 20 MHz 40 MHz Pad = 0



PAD



40 MHz



20 MHz



10 MHz



8 MHz



4 MHz



2 MHz



1 MHz



40



39



38



37



36



35



34



33



41 43 44 45 46 47 48



Pad = 0 Pad = 0 Pad = 0 Pad = 0 Pad = 0 Pad = 0 Pad = 0



PAD



PAD



PAD



PAD



PAD



PAD



PAD



PAD



48



47



46



45



44



43



42



41



*Unit ID (identifier) bits are defined below: BIT 10



BIT 9



UNIT ID



VHF-21( ) UID STRAPS



VHF-22( ) UID STRAPS



0 0 1 1



0 1 0 1



All units 1 2 3



P1-19/20 gnd P1-19/20 open P1-19 open/P1-20 gnd P1-19 gnd/P1-20 open



P1-27/28 open P1-27 open/P1-28 gnd P1-27 gnd/P1-28 open



The VHF-21( )/22( ) will not accept tune information if the unit ID does not match the unit ID straps. UID straps on the VHF-21( ) are P1-19 and P1-20; on the VHF-22( ), they are P1-27 and P1-28.



Revised 1 October 2001



5-25



maintenance 523-0771859 Table 5–9. CSDB Comm Data Output Word — Hex 11. BYTE



BIT



DEFINITION



0



1 2 3 4 5 6 7 8



Label = 1 (LSB) Label = 0 Label = 0 Label = 0 Label = 1 Label = 0 Label = 0 Label = 0 (MSB)



1



9 10 11 12 13 14 15 16



*Unit ID *Unit ID Self-test = 1 Active/preset Transmit (1 = on) **Freq limit **Freq limit Freq valid = 1



17 18 19 20 21 22 23 24



2



3



4



5



CSDB CONTROL PROGRAM DISPLAY OF BYTES 1 THROUGH 5



FREQ VALID =1



**FREQ LIMIT



**FREQ LIMIT



XMIT =1



PRESET =1



SELFTEST =1



*UNIT ID



*UNIT ID



16



15



14



13



12



11



10



9



Pad = 0 Pad = 0 Pad = 0 Pad = 0 0.001 MHz 0.002 MHz 0.004 MHz 0.008 MHz



0.008 MHz



0.004 MHz



0.002 MHz



0.001 MHz



PAD



PAD



PAD



PAD



24



23



22



21



20



19



18



17



25 26 27 28 29 30 31 32



0.01 MHz 0.02 MHz 0.04 MHz 0.08 MHz 0.1 MHz 0.2 MHz 0.4 MHz 0.8 MHz



0.8 MHz



0.4 MHz



0.2 MHz



0.1 MHz



0.008 MHz



0.004 MHz



0.002 MHz



0.001 MHz



32



31



30



29



28



27



26



25



33 34 35 36 37 38 39 40



1 MHz 2 MHz 4 MHz 8 MHz 10 MHz 20 MHz 40 MHz Pad = 0



PAD



40 MHz



20 MHz



10 MHz



8 MHz



4 MHz



2 MHz



1 MHz



40



39



38



37



36



35



34



33



41 43 44 45 46 47 48



Pad = 0 Pad = 0 Pad = 0 Pad = 0 Pad = 0 Pad = 0 Pad = 0



PAD



PAD



PAD



PAD



PAD



PAD



PAD



PAD



48



47



46



45



44



43



42



41



*Unit ID (identifier) bits are defined below: BIT 10 BIT 9 UNIT ID VHF-21( ) UID STRAPS VHF-22( ) UID STRAPS 0 0 0 P1-19/20 gnd P1-27/28 gnd 0 1 1 P1-19/20 open P1-27/28 open 1 0 2 P1-19 open/P1-20 gnd P1-27 open/P1-28 gnd 1 1 3 P1-19 gnd/P1-20 open P1-27 gnd/P1-28 open The VHF-21( )/22( ) will not accept tune information if the unit ID does not match the unit ID straps. **Frequency limit bits are defined below: BIT 15 BIT 14 FREQ LIMIT 0 1 135.975 MHz 1 0 136.975 MHz 1 1 151.975 MHz



Revised 1 October 2001



5-26



maintenance 523-0771859 Table 5–10. CSDB Comm Data Output Word (8.33-kHz Channels) — Hex 13. BYTE



BIT



DEFINITION



0



1 2 3 4 5 6 7 8



Label = 1 (LSB) Label = 1 Label = 0 Label = 0 Label = 1 Label = 0 Label = 0 Label = 0 (MSB)



1



9 10 11 12 13 14 15 16



*Unit ID *Unit ID Self-test = 1 Active/preset Transmit (1 = on) **Freq limit **Freq limit Freq valid = 1



17 18 19 20 21 22 23 24



2



3



4



5



CSDB CONTROL PROGRAM DISPLAY OF BYTES 1 THROUGH 5



FREQ VALID =1



**FREQ LIMIT



**FREQ LIMIT



XMIT =1



PRESET =1



SELF TEST =1



*UNIT ID



*UNIT ID



16



15



14



13



12



11



10



9



Pad = 0 Pad = 0 Pad = 0 Pad = 0 0.001 MHz 0.002 MHz 0.004 MHz 0.008 MHz



0.008 MHz



0.004 MHz



0.002 MHz



0.001 MHz



PAD



PAD



PAD



PAD



24



23



22



21



20



19



18



17



25 26 27 28 29 30 31 32



0.01 MHz 0.02 MHz 0.04 MHz 0.08 MHz 0.1 MHz 0.2 MHz 0.4 MHz 0.8 MHz



0.8 MHz



0.4 MHz



0.2 MHz



0.1 MHz



0.08 MHz



0.04 MHz



0.02 MHz



0.01 MHz



32



31



30



29



28



27



26



25



33 34 35 36 37 38 39 40



1 MHz 2 MHz 4 MHz 8 MHz 10 MHz 20 MHz 40 MHz Pad = 0



PAD



40 MHz



20 MHz



10 MHz



8 MHz



4 MHz



2 MHz



1 MHz



40



39



38



37



36



35



34



33



41 43 44 45 46 47 48



Pad = 0 Pad = 0 Pad = 0 Pad = 0 Pad = 0 Pad = 0 Pad = 0



PAD



PAD



PAD



PAD



PAD



PAD



PAD



PAD



48



47



46



45



44



43



42



41



*Unit ID (identifier) bits are defined below: BIT 10 BIT 9 UNIT ID VHF-21( ) UID STRAPS VHF-22( ) UID STRAPS 0 0 0 P1-19/20 gnd P1-27/28 gnd 0 1 1 P1-19/20 open P1-27/28 open 1 0 2 P1-19 open/P1-20 gnd P1-27 open/P1-28 gnd 1 1 3 P1-19 gnd/P1-20 open P1-27 gnd/P1-28 open The VHF-21( )/22( ) will not accept tune information if the unit ID does not match the unit ID straps. **Frequency limit bits are defined below: BIT 15 BIT 14 FREQ LIMIT 0 1 135.975 MHz 1 0 136.975 MHz 1 1 151.975 MHz



Revised 1 October 2001



5-27



maintenance 523-0771859 Table 5–11. CSDB Comm Frequency Input Word Structure OPERATING FREQUENCY (MHZ)



CHANNEL NAME (CONTROL HEAD)



CSDB HEX ADDRESS (10 = 25 KHZ CHANNELS) (12 = 8.33 KHZ CHANNELS)



CSDB DATA WORD CONTENT



118.0000



118.000



10



18.000



118.0000



118.005



12



18.000



118.0083



118.010



12



18.008



118.0167



118.015



12



18.017



118.0250



118.025



10



18.025



118.0250



118.030



12



18.025



118.0333



118.035



12



18.033



118.0416



118.040



12



18.042



118.0500



118.050



10



18.050



118.0500



118.055



12



18.050



118.0583



118.060



12



18.058



118.0667



118.065



12



18.067



118.0750



118.075



10



18.075



118.0750



118.080



12



18.083



118.0833



118.085



12



18.083



118.0917



118.090



12



18.092



118.1000



118.100



10



18.100



118.10000



118.105



12



18.100



etc.



Revised 1 October 2001



5-28



maintenance 523-0771859 Table 5–12. CSDB Comm Data Output Word Structure OPERATING FREQUENCY (MHZ)



CHANNEL NAME (CONTROL HEAD)



CSDB HEX ADDRESS (11 = 25 KHZ CHANNELS) (13 = 8.33 KHZ CHANNELS)



CSDB DATA WORD CONTENT



118.0000



118.000



11



18.000



118.0000



118.005



13



18.000



118.0083



118.010



13



18.008



118.0167



118.015



13



18.017



118.0250



118.025



11



18.025



118.0250



118.030



13



18.025



118.0333



118.035



13



18.033



118.0416



118.040



13



18.042



118.0500



118.050



11



18.050



118.0500



118.055



13



18.050



118.0583



118.060



13



18.058



118.0667



118.065



13



18.067



118.0750



118.075



11



18.075



118.0750



118.080



13



18.083



118.0833



118.085



13



18.083



118.0917



118.090



13



18.092



118.1000



118.100



11



18.100



118.10000



118.105



13



18.100



etc.



Revised 1 October 2001



5-29



maintenance 523-0771859 Table 5–13. CSDB Diagnostic Output Word — Hex F3. BYTE



BIT



DEFINITION



0



1 2 3 4 5 6 7 8



Label = 1 (LSB) Label = 1 Label = 0 Label = 0 Label = 1 Label = 1 Label = 1 Label = 1 (MSB)



1



9 10 11 12 13 14 15 16



*Unit ID *Unit ID Test = 1 Pad = 0 Fault = 1 Pad = 0 Pad = 0 Pad = 0



2



17 18 19 20 21 22 23 24



Tuning voltage out of limit at highest receive frequency Tuning voltage out of limit at 118 MHz Local oscillator output below limit No-signal AGC voltage below limit Inadequate AGC voltage increase with RF signal Reflected RF power above limit Transmitter timed out Not assigned



3



25 26 27 28 29 30 31 32



Not assigned Bcd frequency code invalid 2 × 5 frequency code invalid CSDB message invalid Frequency out of range Forward RF power below limit Transmitter temperature above limit Not assigned



4



33 34 35 36 37 38 39 40



+5-V dc power below limit +5-V dc power above limit +12-V dc power below limit +12-V dc power above limit Synthesizer not locked Not assigned Noise squelch open without signal Noise squelch not open with signal



5



41 42 43 44 45 46 47 48



1 2 4 8 1 2 4 8



Least significant diagnostic code digit (bcd)



See Table 5–18 for a list of diagnostic codes.



Most significant diagnostic code digit (bcd)



*Unit ID (identifier) bits are defined below: BIT 10



BIT 9



UNIT ID



0 0 1 1



0 1 0 1



0 1 2 3



VHF-21( ) UID STRAPS



VHF-22( ) UID STRAPS



P1-19/20 gnd P1-19/20 open P1-19 open/P1-20 gnd P1-19 gnd/P1-20 open



P1-27/28 gnd P1-27/28 open P1-27 open/P1-28 gnd P1-27 gnd/P1-28 open



The VHF-21( )/22( ) will not accept tune information if the unit ID does not match the unit ID straps.



Revised 1 October 2001



5-30



maintenance 523-0771859 Table 5–14. CSDB Bench Test Input Word — Hex F1. (Bit definitions for this word are provided for reference only.) BYTE



BIT



DEFINITION



0



1 2 3 4 5 6 7 8



Label = 1 (LSB) Label = 0 Label = 0 Label = 0 Label = 1 Label = 1 Label = 1 Label = 1 (MSB)



1



9 10 11 12 13 14 15 16



*Unit ID *Unit ID Self-test = 1 Active/preset Squelch (1 = disabled) XFR tone Pad = 0 Freq valid = 1



2



17 18 19 20 21 22 23 24



Pad = 0 Pad = 0 Pad = 0 Pad = 0 0.001 MHz 0.002 MHz 0.004 MHz 0.008 MHz



3



25 26 27 28 29 30 31 32



0.01 MHz 0.02 MHz 0.04 MHz 0.08 MHz 0.1 MHz 0.2 MHz 0.4 MHz 0.8 MHz



4



33 34 35 36 37 38 39 40



1 MHz 2 MHz 4 MHz 8 MHz 10 MHz 20 MHz 40 MHz Pad = 0



5



41 42 43 44 45 46 47 48



1 (LSB) Diagnostic request code 2 3 4 5 6 7 (MSB) Diagnostic request code Xmit inhibit = 0



BITS 47-41



*Unit ID (identifier) bits are defined below: BIT 10 BIT 9 UNIT ID 0 0 0 0 1 1 1 0 2 1 1 3



VHF-21( ) UID STRAPS P1-19/20 gnd P1-19/20 open P1-19 open/P1-20 gnd P1-19 gnd/P1-20 open



000 0000 000 0010 000 0011 000 1011 001 0001 001 0010 001 0101 001 0110 001 0111 001 1000



DIAGNOSTIC DATA REQUESTED Main µP software rev level Preselector tuning voltage Local oscillator injection voltage AGC voltage +5-V dc power supply voltage +12-V dc power supply voltage Stops heartbeat pulse, resets µP Transmitter temperature Forward transmit power Reflected transmit power



VHF-22( ) UID STRAPS P1-27/28 gnd P1-27/28 open P1-27 open/P1-28 gnd P1-27 gnd/P1-28 open



The VHF-21( )/22( ) will not accept tune information if the unit ID does not match the unit ID straps.



Revised 1 October 2001



5-31



maintenance 523-0771859 Table 5–15. Final Performance (Customer Acceptance) Test For Use With ISA Computer. STEP



PROCEDURE



DESIRED RESULTS



The radio will be strapped by the test computer as follows unless otherwise stated: SERIAL/PARALLEL SELECT



SERIAL (CSDB)



UNIT IDENT A



OPEN (COMM 1)



SIMULCOMM



OPEN (OFF)



KEYLINE



OPEN (REC MODE)



UNIT IDENT B



OPEN (COMM 1)



SQUELCH DISABLE



ENABLED (SQUELCH OFF)



RECEIVER COMPRESSOR DISABLE (VHF-22( ) ONLY)



ENABLED (COMPRESSOR OFF) Note



Optional selectivity test in steps 13.6 through 13.9 requires the use of a generator with a low-noise threshold. Recommended generators are Marconi/IFR 2040, 2023 and Hewlett Packard 8657B or equivalent. If this test is to be performed, it is recommended that the required generator type be used during initial test set-up. Note The cover must be in place and securely fastened during the following tests. 1



CSDB Differential Output Test Computer tunes comm transceiver to 135.000 MHz. Connect one oscilloscope lead to one of two CSDB DATA OUT jacks and gnd to the black RCVR AUDIO jack on test fixture. Connect another oscilloscope lead to the second CSDB DATA OUT jack. Press RETURN to continue.



Verify 12.5 kHz digital data is present on both oscilloscope leads. Enter Y (yes) or N (no).



Disconnect oscilloscope after test. 2



CSDB (Serial) Control Test



2.1



CSDB (Serial) Control 121.975 MHz Computer tunes transceiver to 121.975 MHz and verifies frequency.



2.2



CSDB (Serial) Control 122.000 MHz Computer tunes transceiver to 122.000 MHz and sets unit ident to Comm 2.



2.3



Computer verifies CSDB frequency is 122.000 MHz.



CSDB (Serial) Control 123.000 MHz Computer tunes transceiver to 123.000 MHz and sets unit ident to Comm 3.



3



Computer verifies CSDB frequency is 121.975 MHz.



Computer verifies CSDB frequency is 123.000 MHz.



Parallel (2 X 5) Control Test Note



The following tests, steps 3.1 through 3.3, do not verify accuracy of the transmitted signal frequency. Tolerances have been widened to avoid a transmitter failure from appearing to be a control failure. However, a transmitter failure may still cause a failure in this test. Transmitter frequency accuracy is tested in a later step. 3.1



Parallel (2 X 5) Control 118.000 MHz Computer tunes radio to 118.000 MHz and serial/parallel strapped to parallel. Connect a frequency counter thru a 50-Ω, 50-W, 40-dB power attenuator to the antenna coax connector. Set KEYLINE to CLOSED (transmitter keyed). Return KEYLINE to OPEN after verification.



3.2



Enter frequency. Computer verifies frequency is between 117.988 and 118.012 MHz.



Parallel (2 X 5) Control 123.825 MHz Computer tunes radio to 123.825 MHz and serial/parallel strapped to parallel. Set KEYLINE to CLOSED (transmitter keyed). Return KEYLINE to OPEN after verification.



Revised 1 October 2001



Enter frequency. Computer verifies frequency is between 123.813 and 123.837 MHz.



5-32



maintenance 523-0771859 Table 5–15. Final Performance (Customer Acceptance) Test For Use With ISA Computer. STEP 3.3



PROCEDURE



DESIRED RESULTS



Parallel (2 X 5) Control 131.375 MHz Computer tunes radio to 131.375 MHz and serial/parallel strapped to parallel. Set KEYLINE to CLOSED (transmitter keyed). Return KEYLINE to OPEN after verification.



Enter frequency. Computer verifies frequency is between 131.363 and 131.387 MHz.



End of Control Tests 4



Receiver Sensitivity Test Computer tunes transceiver to 118.000 MHz, sets tune mode to CSDB (serial). On VHF-22( ) transceivers, RCVR COMPRESSOR DISABLE discrete is DISABLED. Connect RF signal generator through a 6-dB pad to antenna connector.



4.1



Receiver Sensitivity at 118.000 MHz Adjust RF signal generator for 3 µV, at 118.000 MHz, modulated 30% by 1 kHz. Connect audio power meter to RCVR AUDIO jacks on test set. Measure audio power level at RCVR AUDIO jacks (s+n). Remove modulation from RF signal and measure audio noise level (n).



4.2



Receiver Sensitivity at 127.600 MHz Computer tunes radio to 127.600 MHz. Adjust RF signal generator for 3 µV, at 127.600 MHz, modulated 30% by 1 kHz. Measure audio power level at RCVR AUDIO jacks (s+n). Remove modulation from RF signal and measure audio noise level (n).



4.3



Verify that (s+n)/n is greater than or equal to 6 dB.



Verify that (s+n)/n is greater than or equal to 6 dB.



Receiver Sensitivity at 135.975 or 136.975 MHz Computer tunes radio to 135.975 or 136.975 MHz. Reduce primary power supply voltage to 22.0 ±0.5 V dc. Press RETURN to continue. Adjust RF signal generator for 3 µV, at the highest frequency (135.975 or 136.975 MHz), modulated 30% by 1 kHz. Measure audio power level at RCVR AUDIO jacks (s+n). Remove modulation from RF signal and measure audio noise level (n).



Verify that (s+n)/n is greater than or equal to 6 dB.



Reset primary power supply voltage to 27.5 ±0.5 V dc. 4.4



Receiver Sensitivity at 151.975 MHz (VHF-21/22 (B/D) only) Computer tunes radio to 151.975 MHz. Ensure that primary power supply voltage is reduced to 22.0 ±0.5 V dc. Adjust RF signal generator for 3 µV, at 151.975 MHz, modulated 30% by 1 kHz. Measure audio power level at RCVR AUDIO jacks (s+n). Remove modulation from RF signal and measure audio noise level (n).



Verify that (s+n)/n is greater than or equal to 6 dB for VHF-22(B) and 4.5 dB for VHF-22(D).



Reset primary power supply voltage to 27.5 ±0.5 V dc. 5



Receiver Residual Output and Quieting Test Computer tunes transceiver to 127.600 MHz. Connect RF signal generator through a 6-dB pad to antenna connector. Adjust RF generator for 100 µV, at 127.600 MHz, modulated 30% by 1 kHz. Connect audio power meter to RCVR AUDIO jacks. Measure audio power level at RCVR AUDIO jacks (s+n). Remove modulation from RF signal and measure audio noise level (n).



6



Simulcomm Test



6.1



Simulcomm Level – ON (on VHF-22( ) without SB 22) Computer tunes radio to 127.600 MHz and selects SIMULCOMM to GND (on). Connect RF signal generator through a 6-dB pad to antenna connector. Apply a 10-µV, 127.600-MHz signal modulated 30% by 1000 Hz. Adjust the RF level to obtain a signal-to-noise (SINAD) ratio of 6 ±1dB.



Revised 1 October 2001



Verify (s+n)/n is greater than or equal to 30 dB.



Enter the RF signal level in µV (range is 3.0 to 10.0 µV). Press RETURN to continue.



5-33



maintenance 523-0771859 Table 5–15. Final Performance (Customer Acceptance) Test For Use With ISA Computer. STEP 6.2



PROCEDURE



DESIRED RESULTS



Simulcomm Level – OFF (on VHF-22( ) without SB 22) Computer selects SIMULCOMM to OPEN (off). Apply a 3.2-µV, 127.600-MHz signal modulated 30% by 1000 Hz. Adjust the RF level to obtain a signal-to-noise (SINAD) ratio of 6 ±1dB.



6.3



Enter the RF signal level in µV (range is 1.0 to 3.2 µV). Press RETURN to continue.



Simulcomm Level – Attenuation (on VHF-22( ) without SB 22) Applicable only to units with SB 22 installed



6.1



Simulcomm Level – ON (on VHF-22( ) with SB 22) Computer tunes radio to 127.600 MHz, selects SIMULCOMM to GND (on). Connect RF signal generator through a 6-dB pad to antenna connector. Apply a 16µV, 127.600-MHz signal modulated 30% by 1000 Hz. Adjust the RF level to obtain a signal-to-noise (SINAD) ratio of 6 ±1dB.



6.2



Simulcomm Level – OFF (on VHF-22( ) with SB 22) Computer selects SIMULCOMM to OPEN (off). Apply a 3.2 µV 127.600-MHz signal modulated 30% by 1000 Hz. Adjust the RF level to obtain a signal-to-noise (SINAD) ratio of 6 ±1dB.



6.3



Enter the RF signal level in µV (range is 7.1 to 22.5 µV). Press RETURN to continue.



Enter the RF signal level in µV (range is 1.0 to 3.2 µV). Press RETURN to continue.



Simulcomm Level – Attenuation (on VHF-22( ) with SB 22) Computer calculates results. (6-dB signal-to-noise ratio with SIMULCOMM on minus 6-dB signal-to-noise ratio with SIMULCOMM off.)



Computer verifies the difference between RF levels. For 687-0960004 thru -007 receiver cards, the difference is 19 ± 1 db. For all other receiver cards the difference is 15 to 20 dB. Press ENTER to continue.



7



Receiver AGC Test Connect RF generator through a 6-dB pad to antenna connector. Computer tunes radio to 127.600 MHz, sets SIMULCOMM to off, RCVR COMPRESSOR DISABLE discrete to DISABLED and SQUELCH DISABLE discrete to ENABLED.



7.1



Receiver AGC Modulated Test Adjust RF generator for 1 mV, at 127.600 MHz modulated 30% by 1 kHz. Measure audio power at RCVR AUDIO jacks and record as a reference level. Observe audio output level as RF signal is varied slowly from 5 µV to 1.0 V.



7.2



Variation between maximum and minimum levels shall be less than or equal to 3 dB.



Receiver AGC Not Modulated Test Remove RF generator from antenna connector. Measure voltage at RCVR AGC jacks. Enter RCVR AGC voltage. Press RETURN to continue.



For 687-0960-004 thru -007 receiver cards, verify AGC voltage is greater than 1.75 V dc. For all other receiver cards, verify AGC voltage is greater than 1.15 Vdc.



8



Receiver Audio Output Test Note Factory nominal levels are specified. Customer level may be different for particular installations. Connect RF generator through a 6-dB pad to antenna connector. The computer tunes transceiver to 127.600 MHz, sets RCVR COMPRESSOR DISABLE discrete to OFF, and SQUELCH DISABLE discrete to ENABLED.



Revised 1 October 2001



5-34



ROCKWELL COLLINS INSTRUCTION BOOK (REPAIR MANUAL) VHF-21( )/22( ), PART NO VHF Comm Transceiver VHF-21( )/22( ) VHF Comm Transceiver INSTRUCTION BOOK (REPAIR MANUAL) (523-0771854, 3RD REVISION, DATED JUL 30/02)



TEMPORARY REVISION NO. 23-12-10-02 Insert facing page 5-34, 23-12-10. Subject: Corrected Table 5-15. Step 6.3 without SB 22 is corrected to read as shown. Changes are shown in bold text. Table 5–15. Final Performance (Customer Acceptance) Test For Use With ISA Computer. STEP 6.3



PROCEDURE



DESIRED RESULTS



Simulcomm Level – Attenuation (on VHF-22( ) without SB 22) Computer calculates results. (6-dB signal-to-noise ratio with SIMULCOMM on minus 6-dB signal-to-noise ratio with SIMULCOMM off.)



Temporary Revision 2 523-0771854-32911A



23-12-10



Computer verifies the difference between RF levels. The difference is 6 to 10 dB. Press ENTER to continue.



Page 1 of 1 Nov 26/02



maintenance 523-0771859 Table 5–15. Final Performance (Customer Acceptance) Test For Use With ISA Computer. STEP 8.1



PROCEDURE



DESIRED RESULTS



Receiver Audio COMBINED Output Test Adjust RF generator for 100 µV, at 127.600 MHz modulated 85% by 1 kHz. Measure and enter audio level at COMBINED AUDIO output jacks across a 600Ω load.



8.2



Receive Audio RCVR Output Test Measure and enter audio level at RCVR AUDIO output jacks across a 600-Ω load.



8.3



Factory limit is 6.4 to 9.2 V rms (68 to 141 mW) across a 600-Ω load.



Receiver Audio Sidetone Output Test Measure and enter audio level at SIDETONE output jacks across a 600-Ω load.



9



Factory limit is 6.4 to 9.2 V rms (68 to 141 mW) across a 600-Ω load.



Factory limit is 0.6 V rms (0.6 mW) or less across a 600-Ω load.



Receiver Audio Compressor Test (Not required when testing a VHF-21( )). Note



The following audio compressor test is valid for all VHF-22( ). The VHF-21( ) is delivered with the receiver audio compressor disabled so that it is directly interchangeable with a VHF-20( ). If the audio compressor is desired in a particular installation, a strap must be removed from the receiver circuit card A2 (reference strapping options). Computer tunes transceiver to 127.600 MHz, sets RCVR COMPRESSOR DISABLE discrete to ON, and SQUELCH DISABLE discrete to ENABLED. Connect RF generator through a 6-dB pad to antenna connector. Adjust RF signal generator for 100 µV, at 127.600 MHz, modulated 85% by 1kHz. Measure audio power at RCVR AUDIO jacks and record as a reference level. Reduce modulation to 30 percent. Calculate reference – reduced and enter results. 10



Verify audio power level does not vary more than 3 dB from reference.



Frequency Response Test Computer tunes transceiver to 127.600 MHz, sets RCVR COMPRESSOR DISABLE discrete to OFF, SQUELCH DISABLE discrete to ENABLED, and SIMULCOMM to OPEN (OFF). Connect RF generator through a 6-dB pad to antenna connector.



10.1



Receiver Audio Frequency Response at 350 Hz Adjust RF signal generator for 100 µV, at 127.600 MHz, modulated 30% by 1kHz. Measure audio power at RCVR AUDIO jacks and record as a reference level. Change modulation frequency to 350 Hz. Calculate reference – reduced and enter results.



10.2



Receiver Audio Frequency Response at 2500 Hz Adjust RF signal generator for 100 µV, at 127.600 MHz, modulated 30% by 1kHz. Measure audio power at RCVR AUDIO jacks and record as a reference level. Change modulation frequency to 2500 Hz. Calculate reference – reduced and enter results.



10.3



Verify audio power level does not drop more than 6 dB below reference.



Receiver Audio Frequency Response at 4000 Hz Adjust RF signal generator for 100 µV, at 127.600 MHz, modulated 30% by 1kHz. Measure audio power at RCVR AUDIO jacks and record as a reference level. Change modulation frequency to 4000 Hz. Calculate reference – reduced and enter results.



11



Verify audio power level does not drop more than 6 dB below reference.



Verify audio power level drops greater than or equal to 18 dB below reference.



Receiver SELCALä Test Computer tunes radio to 127.600 MHz, selects RCVR COMPRESSOR DISABLE discrete to DISABLED, SQUELCH DISABLE discrete to DISABLED, and SIMULCOMM to OPEN (off). Connect RF generator through a 6-dB pad to the antenna connector. Adjust RF signal generator for 1000 µV, at 127.600 MHz, modulated 30% by 1000 Hz.



Revised 1 October 2001



Verify that SELCALä output level is 0.5 V rms (0.4 mW) or greater across 600-Ω load. Record for reference.



5-35



maintenance 523-0771859 Table 5–15. Final Performance (Customer Acceptance) Test For Use With ISA Computer. STEP 12



PROCEDURE



DESIRED RESULTS



Receiver Squelch Test Computer tunes radio to 127.600 MHz, selects RCVR COMPRESSOR DISABLE discrete to DISABLED, SQUELCH DISABLE discrete to ENABLED, and SIMULCOMM to OPEN (off). Connect RF generator through a 6-dB pad to the antenna connector.



12.1



Noise Squelch Test Note



Factory nominal squelch level is set at 3 µV on VHF-21/22(A/B) and 2.7 µV on VHF-21/22(C/D). Customers can set squelch up to a maximum of 10 µV. Customer level may be different for particular installations. 12.1.1



Noise Squelch Disabled Test - 25-kHz Mode Adjust RF signal generator for 3 µV, at 127.600 MHz, modulated 30% by 1000 Hz. Measure the audio level at the RCVR AUDIO jacks across a 600-Ω load.



12.1.2



Noise Squelch Enabled Test - 25-kHz Mode Adjust RF signal generator for 1 µV, at 127.600 MHz, modulated 30% by 1000 Hz. Measure audio level at RCVR AUDIO jacks across a 600-Ω load.



12.1.3



Verify audio level is less than 5 mV rms.



Noise Squelch Disabled Test - 8-kHz Mode (VHF-21/22(C/D) only) Adjust RF signal generator for 3 µV, at 127.600 MHz, modulated 30% by 1000 Hz. Measure the audio level at the RCVR AUDIO jacks across a 600-Ω load.



12.1.4



Verify audio level is 1.0 V rms or greater.



Verify audio level is 1.0 V rms or greater.



Noise Squelch Enabled Test - 8-kHz Mode (VHF-21/22(C/D) only) Adjust RF signal generator for 0.7 µV, at 127.600 MHz, modulated 30% by 1000 Hz. Measure audio level at RCVR AUDIO jacks across a 600-Ω load.



12.2



Carrier Squelch Test



12.2.1



VHF-21/22(A/B) Procedure



12.2.1.1



Preferred Method



Verify audio level is less than 5 mV rms.



Note Use alternate method 1 (step 12.2.1.2) or alternate method 2 (step 12.2.1.3) for testing carrier squelch on the VHF-21/22( ) when a signal generator with simultaneous AM and FM capability is not available. 12.2.1.1.1



Adjust RF signal generator for 30 µV (set RF signal to 24 µV if required for CAA), at 127.600 MHz. Simultaneously frequency modulate (FM) the RF signal with an 8-kHz audio tone at 5 kHz deviation and amplitude modulate (AM) 30% by a 1 kHz with an external modulation source. Computer tunes radio to 127.600 MHz. Measure audio at RCVR AUDIO jacks across a 600- Ω load.



Verify voltage at RCVR AUDIO jacks is 1.0 V rms or greater.



12.2.1.1.2



Reduce RF signal level to 10 µV. After desired results go to step 12.3.



Verify voltage at RCVR AUDIO jacks is less than 5 mV rms.



12.2.1.2



Alternate Method 1



12.2.1.2.1



Adjust RF signal generator for 30 µV (set RF signal to 24 µV if required for CAA), at 127.600 MHz. Modulate the RF signal with AM only at 95%. Modulating frequency may be varied from 7 to 10 kHz. Computer tunes radio to 127.600 MHz. Measure audio at RCVR AUDIO jacks across a 600- Ω load.



Verify voltage at RCVR AUDIO jacks is 1.0 V rms or greater.



12.2.1.2.2



Reduce RF signal level to 10 µV.



Verify voltage at RCVR AUDIO is less than 5 mV rms.



Revised 1 October 2001



5-36



ROCKWELL COLLINS INSTRUCTION BOOK (REPAIR MANUAL) VHF-21( )/22( ) VHF Comm Transceiver VHF-21( )/22( ) VHF Comm Transceiver INSTRUCTION BOOK (REPAIR MANUAL) (523-0771854, 3RD REVISION, DATED JUL 30/02)



TEMPORARY REVISION NO. 23-12-10-13 Insert facing page 5-36, 23-12-10. This temporary revision supersedes Temporary Revision 11 page 1. Subject: Carrier squelch setting changed. No changes were made to this temporary revision page. Table 5–15. Final Performance (Customer Acceptance) Test For Use With ISA Computer. STEP



PROCEDURE



12.2



Carrier Squelch Test



12.2.1



VHF-21/22(A/B) Procedure



12.2.1.1



Preferred Method



DESIRED RESULTS



Note Use alternate method 1 (step 12.2.1.2) or alternate method 2 (step 12.2.1.3) for testing carrier squelch on the VHF-21/22( ) when a signal generator with simultaneous AM and FM capability is not available. 12.2.1.1.1



Adjust RF signal generator for 24 µV, at 127.600 MHz. Simultaneously frequency modulate (FM) the RF signal with an 8-kHz audio tone at 5 kHz deviation and amplitude modulate (AM) 30% by a 1 kHz with an external modulation source. Computer tunes radio to 127.600 MHz. Measure audio at RCVR AUDIO jacks across a 600- Ω load.



Verify voltage at RCVR AUDIO jacks is 1.0 V rms or greater.



12.2.1.1.2



Reduce RF signal level to 10 µV. After desired results go to step 12.3.



Verify voltage at RCVR AUDIO jacks is less than 5 mV rms.



12.2.1.2



Alternate Method 1



12.2.1.2.1



Adjust RF signal generator for 24 µV, at 127.600 MHz. Modulate the RF signal with AM only at 95%. Modulating frequency may be varied from 7 to 10 kHz. Computer tunes radio to 127.600 MHz. Measure audio at RCVR AUDIO jacks across a 600- Ω load.



Temporary Revision 13 523-0771854-3D911A



23-12-10



Verify voltage at RCVR AUDIO jacks is 1.0 V rms or greater.



Page 1 of 4 Oct 10/05



ROCKWELL COLLINS INSTRUCTION BOOK (REPAIR MANUAL) VHF-21( )/22( ) VHF Comm Transceiver VHF-21( )/22( ) VHF Comm Transceiver INSTRUCTION BOOK (REPAIR MANUAL) (523-0771854, 3RD REVISION, DATED JUL 30/02)



TEMPORARY REVISION NO. 23-12-10-13 Insert facing page 5-37, 23-12-10. This temporary revision supersedes Temporary Revision 11 page 2. Subject: Carrier squelch setting changed. Changes identified by black bars in the margin. Table 5–15. Final Performance (Customer Acceptance) Test For Use With ISA Computer. STEP



PROCEDURE



DESIRED RESULTS



12.2.1.3



Alternate Method 2 (VHF-22(A/B) only)



12.2.1.3.1



Adjust RF signal generator for 24 µV, at 127.600 MHz. Remove modulation from the signal generator. Computer tunes radio to 127.600 MHz.



Verify voltage at pin 5 of the rear connector is 11 ±2 V dc.



12.2.1.3.2



Reduce RF signal level to 10 µV.



Verify voltage at pin 5 of the rear connector is 1.5 ±1.5 V dc.



12.2.2



VHF-21/22(C/D) Procedure



12.2.2.1



Adjust RF signal generator for 24 µV, at 127.600 MHz. Simultaneously amplitude modulate (AM) the RF signal with an 8-kHz audio tone at 50% modulation and a 1 kHz tone at 30% modulation. Computer tunes radio to 127.600 MHz. Measure audio at RCVR AUDIO jacks across a 600-Ω load.



Temporary Revision 13 523-0771854-3D911A



23-12-10



Verify voltage at RCVR AUDIO jacks is 1.0 V rms or greater.



Page 2 Oct 10/05



maintenance 523-0771859 Table 5–15. Final Performance (Customer Acceptance) Test For Use With ISA Computer. STEP



PROCEDURE



DESIRED RESULTS



12.2.1.3



Alternate Method 2 (VHF-22(A/B) only)



12.2.1.3.1



Adjust RF signal generator for 30 µV (set RF signal to 24 µV if required for CAA), at 127.600 MHz. Remove modulation from the signal generator. Computer tunes radio to 127.600 MHz.



Verify voltage at pin 5 of the rear connector is 11 ±2 V dc.



12.2.1.3.2



Reduce RF signal level to 10 µV.



Verify voltage at pin 5 of the rear connector is 1.5 ±1.5 V dc.



12.2.2



VHF-21/22(C/D) Procedure



12.2.2.1



Adjust RF signal generator for 30 µV (set RF signal to 20 µV if required for CAA), at 127.600 MHz. Simultaneously amplitude modulate (AM) the RF signal with an 8-kHz audio tone at 50% modulation and a 1 kHz tone at 30% modulation. Computer tunes radio to 127.600 MHz. Measure audio at RCVR AUDIO jacks across a 600-Ω load.



Verify voltage at RCVR AUDIO jacks is 1.0 V rms or greater.



12.2.2.2



Reduce RF signal level to 10 µV.



Verify voltage at RCVR AUDIO jacks is less than 5 mV rms.



12.3



Receiver Squelch Disable Test Remove RF generator from antenna connector. Computer disables squelch. Measure audio level at RCVR AUDIO jacks.



13



Verify voltage at RCVR AUDIO jacks is greater than 1.0 V rms.



Receiver Selectivity Test Note



This test is not required for returning transceiver to service. Unit cover must be in place and secured during the following test. Allow 15 minutes for unit warm-up. Computer tunes transceiver to 127.600 MHz, sets RCVR COMPRESSOR DISABLE discrete to OFF, SQUELCH DISABLE discrete to ENABLED, and displays the AGC voltage. 13.1



Receiver Selectivity Reference Connect RF generator through a 6-dB pad to antenna connector. Adjust RF signal generator for 10 µV, at 127.600 MHz, unmodulated signal. Record AGC voltage at RCVR AGC jacks on test set. Press RETURN after AGC has settled.



13.2



Receiver Selectivity – 25 kHz Lower –6-dB Test Set RF signal level to 20 µV. Slowly vary RF frequency to find lower –6-dB frequency that produces same AGC voltage as recorded level. Press RETURN after AGC has settled. Enter frequency. Press RETURN to continue.



13.3



On -XX1 units, frequency limit is ≥127.608 MHz. On -XX2 units, frequency limit is ≥127.615 MHz.



Receiver Selectivity – 25 kHz Lower –60-dB Test Set RF signal level to 10000 µV. Slowly vary RF frequency to find lower –60-dB frequency that produces same AGC voltage as recorded level. Press RETURN after AGC has settled. Enter frequency. Press RETURN to continue.



13.5



On -XX1 units, frequency limit is ≤127.592 MHz. On -XX2 units, frequency limit is ≤127.585 MHz.



Receiver Selectivity – 25 kHz Upper –6-dB Test Slowly vary RF frequency to find upper –6-dB frequency that produces same AGC voltage as recorded level. Press RETURN after AGC has settled. Enter frequency. Press RETURN to continue.



13.4



Pressing RETURN records AGC for use in the next steps.



On -XX1 units, frequency limit is ≥127.582 MHz. On -XX2 units, frequency limit is ≥127.560 MHz.



Receiver Selectivity – 25 kHz Upper –60-dB Test Slowly vary RF frequency to find upper –60-dB frequency that produces same AGC voltage as recorded level. Press RETURN after AGC has settled. Enter frequency. Press RETURN to continue.



Revised 1 October 2001



On -XX1 units, frequency limit is ≤127.618 MHz. On -XX2 units, frequency limit is ≤127.640 MHz.



5-37



maintenance 523-0771859 Table 5–15. Final Performance (Customer Acceptance) Test For Use With ISA Computer. STEP



PROCEDURE



DESIRED RESULTS Note



Steps 13.6 through 13.9 are applicable to VHF-21/22(C/D) units only. These tests are optional and are not required for final acceptance. The use of a generator with a low-noise threshold is required to perform these steps. Recommended generators are Marconi/IFR 2040, 2023 and Hewlett Packard 8657B or equivalent. Note The receiver selectivity test for the VHF-21/22(C/D) uses the bench test word (F1) to derive the AGC voltage. As a result, an occasional 800 Hz tone may be generated by the VHF COMM’s microprocessor. This is not an indication of a failure. 13.6



Receiver Selectivity - 8.33 kHz Lower -6-dB Frequency Apply a 20 µV, 127.600-MHz unmodulated RF signal through a 6 dB pad to the antenna connector. Slowly vary RF frequency to find lower –6-dB frequency that produces same AGC voltage as recorded level (from step 13.1). Press RETURN to continue.



13.7



Receiver Selectivity - 8.33 kHz Upper -6-dB Frequency Slowly vary RF frequency to find upper –6-dB frequency that produces same AGC voltage as recorded level. Press ENTER to continue.



13.8



Frequency limit is ≥ 127.6028 MHz.



Receiver Selectivity - 8.33 kHz Lower -60-dB Frequency Apply a 10000 µV, 127.600-MHz unmodulated RF signal through a 6 dB pad to the antenna connector. Slowly vary RF frequency to find lower –60-dB frequency that produces same AGC voltage as recorded level. Press RETURN to continue.



13.9



Frequency limit is ≤ 127.5972 MHz.



Frequency limit is ≥ 127.5930 MHz.



Receiver Selectivity - 8.33 kHz Upper -60-dB Frequency Slowly vary RF frequency to find upper –60-dB frequency that produces same AGC voltage as recorded level. Press RETURN to continue.



Frequency limit is ≤ 127.6070 MHz.



End of Receiver Tests Caution Disconnect RF generator from transceiver before continuing with transmitter steps. Observe 30-second transmit, 5-minute receive duty cycle whenever the transmitter is used. The duty cycle is used to prevent the transmitter from overheating. If forced-air cooling is provided, the duty cycle can be extended to 1-minute transmit/4-minute receive. 14



Transmitter RF Output Test Note



The cover must be in place and securely fastened during the following tests. The power output measured in the following tests must be measured with a length of coax no longer than 15 cm (6 in) between transceiver and wattmeter. 14.1



RF Output at 118.050 MHz Connect 50-Ω, 50-W RF load and RF wattmeter to antenna connector on transceiver. Computer tunes transceiver to 118.050 MHz. Set KEYLINE switch to CLOSED (observe 30-second/5-minute duty cycle).



14.2



RF Output at 127.700 MHz Computer tunes transceiver to 127.700 MHz. Set KEYLINE switch to CLOSED (observe 30-second/5-minute duty cycle).



14.3



Verify unmodulated RF output power is between 16 and 28 W.



RF Output at 135.875 MHz (on VHF-21/22(A) internally jumpered for max frequency 135.875 MHz) or at 136.875 MHz (on VHF-21/22(A) without internal jumper and all VHF-21/22(C/D) units). Computer tunes transceiver to 135.875 MHz or 136.875 MHz. Set KEYLINE switch to CLOSED (observe 30-second/5-minute duty cycle).



14.4



Verify unmodulated RF output power is between 16 and 28 W.



Verify unmodulated RF output power is between 16 and 28 W.



RF Output at 151.875 MHz (VHF-21/22 (B/D) Only) Computer tunes transceiver to 151.875 MHz. Set KEYLINE switch to CLOSED (observe 30-second/5-minute duty cycle).



Revised 1 October 2001



Verify unmodulated RF output power is between 16 and 28 W.



5-38



maintenance 523-0771859 Table 5–15. Final Performance (Customer Acceptance) Test For Use With ISA Computer. STEP 15



PROCEDURE



DESIRED RESULTS



Transmitter Modulation Test Connect either an RF modulation analyzer or an oscilloscope through a 50-Ω, 50W, 40-dB power attenuator to unit antenna connector. The oscilloscope must be usable at 155 MHz. Note A resistor may be required in series with audio generator output to prevent loading down generator.



15.1



25-kHz Mode



15.1.1



Connect an audio signal generator to AUDIO INPUT jacks on test set. Adjust audio signal generator for a 600 mV rms, 1 kHz signal at AUDIO INPUT. Computer tunes transceiver to 135.875 MHz. Press ENTER to continue. Set KEYLINE switch on test set to CLOSED. Measure and enter percent of modulation depth. Press ENTER to continue.



Verify that modulation depth is at least 85 percent. If an oscilloscope is used, refer to Figure 5–11 to determine depth of modulation.



15.1.2



Increase audio input to 2.40 V rms. Set KEYLINE switch on test set to CLOSED. Establish a reference level for the modulation envelope. Press ENTER to continue.



Verify NGT 95% modulation depth.



15.1.3



Remove audio input from AUDIO INPUT jacks on test set. Set KEYLINE switch on test set to CLOSED. Press ENTER to continue.



Verify that the envelope level is at least 40 dB below that observed in step 15.1.2.



15.2



8.33-kHz Mode (VHF-21/22(C/D) only)



15.2.1



Connect an audio signal generator to AUDIO INPUT jacks on test set. Adjust audio signal generator for a 600 mV rms, 1 kHz signal at AUDIO INPUT. Computer tunes transceiver to 135.875 MHz. Press ENTER to continue. Set KEYLINE switch on test set to CLOSED. Measure and enter percent of modulation depth. Press ENTER to continue.



Verify that modulation depth is at least 85 percent. If an oscilloscope is used, refer to Figure 5–11 to determine depth of modulation.



15.2.2



Increase audio input to 2.40 V rms. Set KEYLINE switch on test set to CLOSED. Establish a reference level for the modulation envelope. Press ENTER to continue.



Verify NGT 95% modulation depth.



15.2.3



Remove audio input from AUDIO INPUT jacks on test set. Set KEYLINE switch on test set to CLOSED. Press ENTER to continue.



Verify that the envelope level is at least 40 dB below that observed in step 15.2.2.



15.2.4



Reconnect 1 kHz audio signal generator input to AUDIO INPUT jacks on test set. Adjust audio input to 600 mV rms. Computer tunes transceiver to 127.700 MHz (8.33-kHz mode). Set KEYLINE switch on test set to CLOSED. Press ENTER to continue.



Verify that the modulation depth is at least 75%.



16



Sidetone and Combined Audio Output Test



Verify that the total harmonic distortion plus noise in the modulation envelope does not exceed 15%.



Verify that the total harmonic distortion plus noise in the modulation envelope does not exceed 15%.



Note Factory nominal levels are specified. Customer level may be different for particular installations. Connect a 50-Ω, 50-W RF load to unit antenna connector. Connect an audio signal generator to AUDIO INPUT jacks on test set. Adjust audio signal generator for 2.4 V rms, 1 kHz signal at AUDIO INPUT. Computer tunes transceiver to 135.875 MHz.



Revised 1 October 2001



5-39



maintenance 523-0771859 Table 5–15. Final Performance (Customer Acceptance) Test For Use With ISA Computer. STEP 16.1



PROCEDURE



DESIRED RESULTS



Sidetone Output Level Key transmitter. Measure audio level at SIDETONE, AUDIO OUTPUT, and RECEIVE AUDIO OUTPUT jacks on the test set across a 600-Ω load. Press ENTER to continue.



Verify 3.9 ±1.0 V rms at SIDETONE and AUDIO OUTPUT jacks. Verify LT 0.6 V rms at RECEIVE AUDIO OUTPUT jacks.



16.2



Combined Audio Output Test Key transmitter and measure audio level at test fixture COMBINED jacks across a 600-Ω load. Enter audio level at combined audio output.



17



Combined audio voltage should be 2.7 to 5.1 V rms (12 to 43 mW) across a 600-Ω load.



Frequency Accuracy Test Note



The frequency limits given are offset at room temperature to allow for normal variations over the operating temperature range of the transceiver. Connect a frequency counter through a 50-Ω, 50-W, 40-dB power attenuator to unit antenna connector (or couple frequency counter in a manner that provides a proper input level to the frequency counter). Press RETURN to continue. Computer tunes transceiver to 135.00 MHz. With no modulation, set KEYLINE switch to CLOSED (observe 30-second/5-minute duty cycle). Enter frequency from counter.



Verify that actual frequency is between 134.9998 and 135.0018 MHz.



End of Transmitter Tests 18



End of Final Performance Test



Revised 1 October 2001



5-40



ROCKWELL COLLINS INSTRUCTION BOOK (REPAIR MANUAL) VHF-21( )/22( ) VHF Comm Transceiver VHF-21( )/22( ) VHF Comm Transceiver INSTRUCTION BOOK (REPAIR MANUAL) (523-0771854, 3RD REVISION, DATED JUL 30/02)



TEMPORARY REVISION NO. 23-12-10-13 Insert facing page 5-40, 23-12-10. This temporary revision supersedes Temporary Revision 11 page 3. Subject: Carrier squelch setting changed. No changes were made to this temporary revision page. Table 5–15. Final Performance (Customer Acceptance) Test For Use With ISA Computer. STEP 17



PROCEDURE



DESIRED RESULTS



Frequency Accuracy Test Note



The frequency limits given are offset at room temperature to allow for normal variations over the operating temperature range of the transceiver. 17.1



Connect a frequency counter through a 50-Ω, 50-W, 40-dB power attenuator to unit antenna connector (or couple frequency counter in a manner that provides a proper input level to the frequency counter). Press RETURN to continue. Computer tunes transceiver to 135.00 MHz. With no modulation, set KEYLINE switch to CLOSED (observe 30-second/5-minute duty cycle). Enter frequency from counter.



17.2



Mic Input Bias Voltage Connect a 50-Ω rf load to the transceiver antenna connector. Monitor the mic input pin with a dmm connected directly and set to measure dc voltage with respect to system ground. Tune the transceiver to 135.00 MHz. With no modulating signal applied, key the transmitter.



Temporary Revision 13 523-0771854-3D911A



23-12-10



Verify that actual frequency is between 134.9998 and 135.0018 MHz.



Verify that the bias voltage is greater than +13.49 V dc.



Page 3 Oct 10/05



maintenance 523-0771859



Figure 5–11. Modulation Depth Calculation



5.4.4 Adjustment/Alignment P rocedures The following procedures should be used to adjust and realign circuits in the transceiver whenever required as indicated by the testing and troubleshooting procedures. Use Table 5–16 with an ISA computer test setup. Note The procedures in Table 5–16 can be used to align either VHF-21/22(A/B) or VHF-21/22(C/D) units when using an ISA computer test setup. Note Always verify proper power supply operation before performing any adjustment or alignment procedures. Refer to Figure 5–14 through Figure 5–24 for location of test points and adjustment controls referenced in Table 5–16.



Revised 24 May 2002



5-41



maintenance 523-0771859 Table 5–16. Alignment/Adjustment Procedures For Use With ISA Computer. STEP



PROCEDURE



DESIRED RESULTS



The radio will be strapped by the test computer as follows unless otherwise stated: SERIAL/PARALLEL SELECT



SERIAL (CSDB)



UNIT IDENT A



OPEN (COMM 1)



SIMULCOMM



OPEN (OFF)



KEYLINE



OPEN (REC MODE)



UNIT IDENT B



OPEN (COMM 1)



SQUELCH DISABLE



DISABLED



RECEIVER COMPRESSOR DISABLE (VHF-22( ) ONLY) 1



Initial Setup



1.1



VHF-21/22(A/B) Procedure



ENABLED (COMPRESSOR DISABLED)



Disconnect primary power and remove transceiver dust cover. Disassemble unit so that receiver card A2 and the synthesizer/control cards can be folded down. If doing alignment after extensive maintenance, make the following adjustments on receiver card A2 (refer to Figure 5–16) and power supply/modulator card A3 (refer to Figure 5– 18): A2R252 max cw (687-0960-004 only) A2R341 max cw (687-0960-004, -006 only) A3R510 max ccw A3R519 max ccw A3R520 max ccw Reapply power to the transceiver. 1.2



VHF-21/22(C/D) Procedure Disconnect primary power and remove transceiver dust cover. Disassemble unit so that receiver card A2 and the synthesizer/control cards can be folded down. If doing alignment after extensive maintenance, make the following adjustments on receiver card A2 (refer to Figure 5–17) and modulator/power supply card A3 (refer to Figure 5–19): A2R252 max cw (687-0960-005 only) A2R341 max cw (687-0960-005, -007 only) A3R503 midpoint A3R504 midpoint A3R505 max ccw A3R511 midpoint A3R512 max ccw A3R518 midpoint A3R573 max ccw Reapply power to the transceiver.



2



Power Supply



2.1



VHF-21/22(A/B) Procedure Set primary power supply to +27.5 ±0.5 V dc. Refer to Figure 5–18 and verify the following voltages on modulator/power supply card A3. TEST POINT



DESIRED VOLTAGE



A3U504-3 (OUT) A3U505-3 (OUT) A3U508-1 (IN) A3U508-3 (OUT)



+12.0 ±1.0 V dc +5.00 ±0.25 V dc +27.0 ±1.0 V dc +12.0 ±1.0 V dc



Revised 1 October 2001



Adjust A4R708 for +5.12 ±0.01 V dc at A4TP7 with respect to chassis ground.



5-42



maintenance 523-0771859
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