31R4-2FRN45-2-33GS-1.pdf

TO 31R4-2FRN45-2-33GS-1

1 SEPTEMBER 2003 Change 4 7 FEBRUARY 2012

TECHNICAL MANUAL

GENERAL EQUIPMENT DESCRIPTION

ORGANIZATIONAL MAINTENANCE

TACAN NAVIGATIONAL SET

AN/FRN-45

PN 880199

DISCLOSURE NOTICE – This information is furnished upon the condition that it will not be released to another nation without the specific authority of the Department of the Air Force of the United States, that it will be used for military purposes only, that individual or corporate rights originating in the information, whether patented or not, will be respected, that the recipient will report promptly to the United States, any known or suspected compromise, and that the information will be provided substantially the same degree of security afforded it by the Department of Defense of the United States. Also, regardless of any other markings on the document, it will not be downgraded or declassified without written approval of the originating United States agency.

DISTRIBUTION STATEMENT D - Distribution authorized to Department of Defense and U.S. DoD contractors only. Due to critical technology (7 February 2012). Other requests for this document shall be referred to OC-ALC/GKAAB, Tinker AFB, Oklahoma 73145-9155.

WARNING - This document contains technical data whose export is restricted by the Arms Export Control Act (Title 22, U.S.C. 2751 et seq.) or Executive Order 12470. Violations of these export laws are subject to severe criminal penalties. Disseminate in accordance with provisions of DoD Directive 5230.25.

HANDLING AND DESTRUCTION NOTICE - Handle in compliance with distribution statement and destroy by any method that will prevent disclosure of the contents or reconstruction of the document.

PUBLISHED UNDER THE AUTHORITY OF THE SECRETARY OF THE AIR FORCE

TO 31R4-2FRN45-2-33GS-1

*Zero in this column indicates an original page

A Change 4 USAF

NOTE: The portion of the text affected by the change is indicated by a vertical line in the outer margins of the page. Changes to illustrations are indicated by miniature pointing hands. Changes to wiring diagrams are indicated by shaded or screened areas.

TOTAL NUMBER OF PAGES IN THIS MANUAL IS 128, CONSISTING OF THE FOLLOWING:

Title A i - ii iii iv - ix x Blank 1-1 - 1-74 2-1 - 2-7

2-8 2-9 - 2-16 2-17 - 2-18 2-19 - 2-27 2-28 Blank 3-1 3-2 Blank 4-1 - 4-2

5-1 5-2 5-3 5-4 Blank A-1 - A-4 B-1 - B-2

Dates of issue for original and changed pages are:

Original . . . . . . . . . . . . . . . . 0 . . . . .1 September 2003 Change . . . . . . . . . . . . . . . . 2 . . . . . . 28 January 2011 Change . . . . . . . . . . . . . . . . 4 . . . . . . 7 February 2012

Change. . . . . . . . . . . . . . . . . 1 . . . . . . . . . 22 June 2009 Change. . . . . . . . . . . . . . . . . 3 . . . . . 22 November 2011

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LIST OF EFFECTIVE PAGES

T.O. 31R4-2FRN45-2-33GS-1

i

TABLE OF CONTENTS

Chapter Title Page

List of Illustrations....................................................................................................................................... iv

List of Tables ............................................................................................................................................... v

Foreword..................................................................................................................................................... vi

Safety Summary ......................................................................................................................................... ix

1 SYSTEM FUNCTIONAL DESCRIPTION

1.1 TACAN Navigational Set (33-00-000)...................................................................................1-1

1.1.1 TACAN Navigational Set Functional Description..................................................................1-1

1.1.2 TACAN Navigational Set Theory of Operation .....................................................................1-1

1.2 Transponder Group (33-05-000).........................................................................................1-11

1.2.1 Transponder Group Functional Description........................................................................1-11

1.2.2 EMI Filter (33-05-100) Theory of Operation........................................................................1-12

1.3 Antenna Group (33-15-000)................................................................................................1-12

1.3.1 Functional Description ........................................................................................................1-12

1.3.2 Antenna...............................................................................................................................1-12

1.3.3 Modulation Generator .........................................................................................................1-12

1.4 Power Supply (33-26-000) ..................................................................................................1-12

1.4.1 Power Supply Functional Description .................................................................................1-12

1.4.2 Power Supply (33-26-000) Theory of Operation.................................................................1-13

1.4.3 TACAN Power Supply Control (33-26-100) Theory of Operation.......................................1-13

1.5 Transponder (33-35-000)....................................................................................................1-16

1.5.1 Transponder Functional Description...................................................................................1-16

1.5.2 Control Indicator Interface (33-35-100) Theory of Operation .............................................1-17

1.5.3 Video Processor (33-35-110) Theory of Operation.............................................................1-20

1.5.4 Programmable Echo Level (33-35-120) Theory of Operation ............................................1-22

1.5.5 Fault Isolation Processor (33-35-130) Theory of Operation ...............................................1-25

1.5.6 Amplitude/Shape Controller (33-35-140) Theory of Operation...........................................1-29

1.5.7 Decoder (33-35-150) Theory of Operation .........................................................................1-32

1.5.8 Burst/Ident Sync Generator (33-35-160) Theory of Operation ...........................................1-33

1.5.9 Encoder (33-35-170) Theory of Operation..........................................................................1-38

1.5.10 Circuit Card Transponder Interconnection (33-35-180) Theory of Operation.....................1-40

1.5.11 400w Power Amplifier (33-35-190) Theory of Operation ....................................................1-40

1.5.12 400w RF Amplifier (33-35-192) and 400w Coupler (33-35-196)

Theory of Operation ............................................................................................................1-40

1.5.13 400w Modulator (33-35-194) Theory of Operation .............................................................1-40

1.5.14 Power Supply Regulator (33-35-220) Theory of Operation ................................................1-42

1.5.15 Receiver (33-35-230) Theory of Operation.........................................................................1-43

1.5.16 Frequency Synthesizer (33-35-240) Theory of Operation ..................................................1-44

1.5.17 100w Power Amplifier (33-35-250) Theory of Operation ....................................................1-46

1.6 Radio Frequency Amplifier (33-37-000)..............................................................................1-50

1.6.1 Radio Frequency Amplifier Functional Description.............................................................1-50

1.6.2 700w Power Amplifier (33-37-100, -110, -120, -130, -140, -150, -160, -170) Theory of Operation.......................................................................1-50 ii

TABLE OF CONTENTS (Continued)

Chapter Title Page

1.6.3 700w Modulator (33-37-102, -112, -122, -132, -142,-152, -162, -172) Theory of Operation ............................................................................................................1-51

1.6.4 Directional Coupler (33-37-180) Theory of Operation ........................................................1-52

1.6.5 Directional Coupler (33-37-260) Theory of Operation ........................................................1-52

1.6.6 HP Amplifier Interconnection Circuit Card (33-37-210) Theory of Operation .....................1-52

1.7 Radio Frequency Monitors A and B (33-45-000 and 33-46-000) .......................................1-53

1.7.1 Radio Frequency Monitors Functional Description .............................................................1-53

1.7.2 Analog Azimuth Monitor (33-45-100 and 33-46-100) Theory of Operation ........................1-59

1.7.3 Digital Azimuth Monitor (33-45-110 and 33-46-110) Theory of Operation .........................1-60

1.7.4 Master Counter Theory of Operation ..................................................................................1-61

1.7.5 Timing Pulse Generator (33-45-130 and 33-46-130) Theory of Operation ........................1-63

1.7.6 Azimuth Monitor Calibrator (33-45-140 and 33-46-140) Theory of Operation....................1-64

1.7.7 Monitor Multiplexer Circuit Card (33-45-150 and 33-46-150)

Theory of Operation ............................................................................................................1-65

1.7.8 Interrogation Trigger Generator (33-45-160 and 33-46-160)

Theory of Operation ............................................................................................................1-66

1.7.9 24K Central Processing Unit (CPU) (33-45-180 and 33-46-180)

Theory of Operation ............................................................................................................1-67

1.7.10 Time Base/Interface (33-45-190 and 33-46-190) Theory of Operation ..............................1-68

1.7.11 Voltage Regulator (33-45-200 and 33-46-200) Theory of Operation..................................1-70

1.7.12 Monitor Interconnection Circuit Card (33-45-210 and 33-46-210)

Theory of Operation ............................................................................................................1-70

1.7.13 Frequency Synthesizer (33-45-220 and 33-46-220) Theory of Operation..........................1-70

1.7.14 Modulator/Detector (33-45-240 and 33-46-240) Theory of Operation................................1-71

1.7.15 Programmable Attenuator (33-45-230 and 33-46-230) Theory of Operation .....................1-71

1.8 Control Indicator (33-50-000)..............................................................................................1-71

1.8.1 Control Indicator Functional Description.............................................................................1-71

1.9 Personal Computer .............................................................................................................1-71

1.9.1 Personal Computer Functional Description ........................................................................1-71

1.9.2 Control Indicator Power Supply (33-60-220) Theory of Operation .....................................1-72

2 SPECIAL MAINTENANCE PROCEDURES

2.1 TACAN Navigational Set (33-00-000)...................................................................................2-1

2.1.1 Test Points ............................................................................................................................2-1

2.1.2 Performance Test Standards ................................................................................................2-1

2.1.3 Performance Test Table........................................................................................................2-1

2.2 TACAN Transponder Group (33-05-000)..............................................................................2-2

2.2.1 Test Points ............................................................................................................................2-2

2.2.2 Performance Test Standards ................................................................................................2-2

2.2.3 Performance Test Tables......................................................................................................2-2

2.2.4 Performance Test Checks.....................................................................................................2-3

2.2.5 Operating Procedures...........................................................................................................2-3

2.2.6 Loss of Data Acquisition Processing System (DAPS) ..........................................................2-6

2.2.7 Operational Test....................................................................................................................2-6

2.2.8 Channel Change ...................................................................................................................2-7

2.3 Power Supply (33-26-000) ....................................................................................................2-7

Change 3 iii

TABLE OF CONTENTS (Continued)

Chapter Title Page

2.3.1 Test Points ............................................................................................................................ 2-7

2.3.2 Performance Test Standards ................................................................................................ 2-7

2.3.3 Performance Test Table ....................................................................................................... 2-7

2.4 Transponder (33-35-000) ...................................................................................................... 2-8

2.4.1 Test Points ............................................................................................................................ 2-8

2.4.2 Performance Test Standards ................................................................................................ 2-8

2.4.3 Performance Test Table ....................................................................................................... 2-8

2.5 Radio Frequency Amplifier (33-37-000) .............................................................................. 2-16

2.5.1 Test Points .......................................................................................................................... 2-16

2.5.2 Performance Test Standards .............................................................................................. 2-16

2.5.3 Performance Test Table ..................................................................................................... 2-16

2.5.4 700 Watt Amplifier Operational Test ................................................................................... 2-18

2.6 Radio Frequency Monitors A and B (33-45-000 and 33-46-000) ....................................... 2-20

2.6.1 Test Points .......................................................................................................................... 2-20

2.6.2 Performance Test Standards .............................................................................................. 2-20

2.6.3 Performance Test Table ..................................................................................................... 2-20

2.7 Control Indicator (33-50-000) .............................................................................................. 2-22

2.7.1 Test Points .......................................................................................................................... 2-22

2.7.2 Performance Test Standards .............................................................................................. 2-22

2.7.3 Performance Test Table ..................................................................................................... 2-22

2.7.4 Preliminary Checkout .......................................................................................................... 2-22

3 CONSUMABLE MATERIALS

3.1 Consumable Materials .......................................................................................................... 3-1

4 SUPPORT EQUIPMENT

4.1 Support Equipment ............................................................................................................... 4-1

5 TACAN FACILITY ANNUAL INSPECTION

5.1 AN/FRN-45 TACAN Facility Annual Inspection .................................................................... 5-1

5.2 Facility Performance Check for Annual Inspection ............................................................... 5-1

Appendix A TACAN Reference Designator - S/S/SN Cross Reference.................................................. A-1

Appendix B TACAN Navigational Set Replacement Index ..................................................................... B-1 iv

LIST OF ILLUSTRATIONS

Figure Title Page

1-1 Typical TACAN Facility and Equipment Locations ...............................................................1-2 1-2 Ground Station Output ..........................................................................................................1-3 1-3 Typical Cockpit Indicators .....................................................................................................1-4 1-4 Interrogation Reply Pulse Code ............................................................................................1-5 1-5 Distance Reply Pulse Code ..................................................................................................1-5 1-6 TACAN Pulse Train...............................................................................................................1-6 1-7 Radiated Antenna Pattern.....................................................................................................1-7 1-8 TACAN Bearing Measurement .............................................................................................1-9 1-9 Transmitted RF Carrier .......................................................................................................1-10 1-10 Gated TACAN Idents ..........................................................................................................1-37 1-11 Power Supply Control Waveshapes ...................................................................................1-74 v

LIST OF TABLES

Number Title Page

1-1 Encoder Logic Conditions and Outputs ..............................................................................1-18 1-2 Tri-State U4 through U9 Data Access and Command Control ...........................................1-26 1-3 Tri-State U4 Data Access ...................................................................................................1-27 1-4 Tri-State U8 Data Access ...................................................................................................1-27 1-5 Tri-State U7 Data Access ...................................................................................................1-27 1-6 Tri-State U6 Data Access ...................................................................................................1-28 1-7 Tri-State U9 Data Access ...................................................................................................1-28 1-8 Echo Self-Test (Tri-State U5 Selected)...............................................................................1-28 1-9 PROM U13 Output Data (Q1 through Q4)..........................................................................1-35 1-10 PROM U13 Output Data (Q5 through Q7)..........................................................................1-35 1-11 Calibration/Test Modes .......................................................................................................1-57

2-1 TACAN Navigational Set Test Points....................................................................................2-1 2-2 TACAN System, Performance Test Standards.....................................................................2-1 2-3 TACAN System, Performance Test Table ............................................................................2-2 2-4 Transponder Group, Test Points...........................................................................................2-4 2-5 Power Supply, Performance Test Standards........................................................................2-7 2-6 Power Supply, Performance Test Table ...............................................................................2-8 2-7 Transponder, Performance Test Standards .........................................................................2-8 2-8 Transponder, Performance Test Table.................................................................................2-9 2-9 Channel Frequency Table...................................................................................................2-10 2-10 Radio Frequency Amplifier, Performance Test Standards .................................................2-17 2-11 Radio Frequency Amplifier, Performance Test Table.........................................................2-18 2-12 Radio Frequency Monitors A and B, Performance Test Standards....................................2-20 2-13 Radio Frequency Monitors A and B, Performance Test Table ...........................................2-21 2-14 Control Indicator, Test Points..............................................................................................2-23 2-15 Control Indicator, Performance Test Standards .................................................................2-24 2-16 Control Indicator, Performance Test Table.........................................................................2-25

3-1 Consumable Materials ..........................................................................................................3-1

4-1 Support Equipment ...............................................................................................................4-1 vi

FOREWORD

1. PURPOSE.

The General System (GS) manual provides functional descriptions of the TACAN Navigational Set to be used by maintenance personnel to further their understanding of the equipment and installed subsystems and sub-subsystems.

2. SCOPE.

The GS manual provides detailed system, subsystem, and sub-subsystem descriptions, theory of operation, and special maintenance information for the TACAN Navigational Set. Special maintenance procedures are included which do not conform to Job Guide (JG) manual format. Also included is a list of consumable materials and support equipment required to accomplish all maintenance procedures.

3. ARRANGEMENT.

The manual is arranged by sections as follows:

CHAPTER 1. System Functional Description

Provides a detailed description and theory of operation of the TACAN Navigational Set. Schematics are referenced as necessary to support the system descriptions. Illustrations are provided showing the appropriate locations of all Line Replaceable Units (LRUs) and Shop Replaceable Units (SRUs).

CHAPTER 2. Special Maintenance Procedures

Provides special maintenance requirements that apply to the TACAN Navigational Set, but which do not conform to the JG manual format.

CHAPTER 3. Consumable Materials

Provides a list of the consumable materials required to accomplish maintenance on the TACAN Navigational Set.

CHAPTER 4. Support Equipment

Provides a list of support equipment required to perform maintenance on the TACAN Navigational Set.

CHAPTER 5. TACAN Facility Certification Requirements

Provides a list of TACAN facility certification requirements.

4. USE OF THIS MANUAL.

A table of contents provides the section, paragraph number, title, and page number of each major paragraph in the manual. A list of illustrations provides the figure number, title, and page number for each illustration. A list of tables provides the table number, title, and page number for each table. The System/ Subsystem/Sub-subsystem Number (S/S/SN) on the outside corner of each page provides a quick reference for locating material throughout the manual.

The word TYPICAL when used on an illustration indicates that two or more configurations exist, but only one configuration is illustrated. The words shall, should, may, and will have the following meanings in this manual set:

Shall is used to express a provision that is mandatory.

vii

Should and may are used to express a provision that is non-mandatory.

Will is used to express a declaration of purpose.

5. WARNINGS, CAUTIONS, and NOTES as used in this manual.

These are defined as follows.

WARNING: An operating or maintenance procedure, practice, condition, statement, etc., which, if not strictly observed, could result in injury to or death of personnel.

Electrical power shall not be connected or applied to the equipment. Failure to comply may cause injury to personnel and damage to equipment.

CAUTION: An operating or maintenance procedure, practice, condition, statement, etc., which, if not strictly observed, could result in damage to or destruction of equipment or loss of mission effectiveness.

Use clean soft cloth, turning frequently for a faster, better finish. To prevent damage, discard when used or contaminated with any abrasive material.

NOTE: An essential operating or maintenance procedure, condition, or statement, which must be highlighted.

NOTE

Polish one access panel at a time to prevent streaking by dried polish.

6. NONSTANDARD ABBREVIATIONS.

Abbreviations used in this manual conform to MIL-STD-12D, except for the following nonstandard abbreviations.

AGR - Automatic Gain Reduction ITG - Interrogation Trigger Generator ALE - Addressable Latch Enable JG - Job Guide AMD - Automatic Monitor Digital MCC - Master Counter Circuit AMT - Automatic Monitor Tests MFT - Monitor Fault CE - Chip Enable MMRD - Memory Mapped Read CI - Control Indicator Interface MMWR - Memory Mapped Write DAPS - Data Acquisition Processing System OE - Output Enable DIP - Dual Inline Package PC - Personal Computer ESDS - Electrostatic Discharge Sensitive SD - Schematic Diagram:

FI - Fault Isolation VKP - VOR Keyer Pulse FTK - Full Time Keying WR - Write GS - General System viii

7. ELECTROSTATIC DISCHARGE SENSITIVE (ESDS) EQUIPMENT.

Electrostatic Discharge Sensitive (ESDS) devices are used in this assembly. Static electricity, can damage these devices. Special handling methods and materials must be used to prevent damage. Do not touch or remove any ESDS device or any assembled circuit board that has an ESDS device without properly grounding your body, test equipment, and all tools. Be thoroughly familiar with the handling procedures specified in T.O. 00-25-234 and T.O. 31-1-141-1. Move or store assembled circuit boards only in conductive (antistatic) bags. Do not touch the printed circuits or the connector pins on the board;

handle the board by the edges only. Keep the pins of an ESDS device shorted together whenever possible; use a device shorting bus, a shorting tube, or conductive foam.

8. CHANGE RECOMMENDATIONS.

Recommendations concerning changes to this manual shall be submitted in accordance with T.O. 00-5-1.

9. RECORD OF APPLICABLE TIME COMPLIANCE TECHNICAL ORDERS (TCTOs).

The following chart sets forth those TCTOs that are applicable to the equipment in this manual.

TCTO Number Title TCTO Date

31R4-2-509 Modification to Install Limited Transmitter Engineering Change Proposal (ECP-27), Power Conversion Engineering Change Proposal (ECP-3O), Power Jack Engineering Change Proposal (ECP-31), and On Request Mode Engineering Change Proposal (ECP-32) for AN/FRN-45 TACAN Navigational Set

1 Nov 90

31R4-2-510 Modification to Install 700 Watt Test Point Engineering Change Proposal (ECP-34) for AN/FRN-45 TACAN Navigational Set

1 Nov 90

31R4-2-511 Modification to Install Audio Engineering Change Proposal (ECP-22) and Power Monitor Display Assembly (Part of ECP-25) for AN/FRN-45 TACAN Navigational Set

1 Nov 90

31R4-2FRN45-501 Modification to Install Burst/Ident Sync Generator Engineering Change Proposal (ECP-43) for AN/FRN-45 TACAN Navigational Set

1 Apr 97

31R4-2FRN45-502 Modification to Install Front Panel Test Points on the AN/FRN-45 TACAN Navigational Set

16 Apr 98

31R4-2FRN45-503 Modification to Install a Second +65 Volt Path for 700-Watt Amplifiers on the AN/FRN-45 TACAN Navigational Set

1 Feb 99

31R4-2FRN45-504 Modification to Install Upgraded EPROMS in the RF Monitors for the

AN/FRN-45 TACAN

1 May 99

31R4-2-FRN45-505 Inspection of Frequency Synthesizer Modules in AN/FRN-45 TACAN Systems

1 Apr 02

31R4-2-FRN45-506 Inspection of TACAN Navigational Set AN/FRN-45 Power Supply, Part Number 105324

21 May 02

31R4-2FRN45-507 Modification to replace FCPU with Personal Computer 1 Sep 03 ix/(x blank)

SAFETY SUMMARY

GENERAL SAFETY NOTICES

1. GENERAL SAFETY NOTICES.

These notices add to the warnings and cautions appearing in other parts of this manual. They remind the user of potential dangers to personnel or damage to the equipment. If safety hazards exist that the general or specific safety precautions do not cover, the commanding officer or other authority issues the necessary orders to cover the hazard.

2. KEEP AWAY FROM LIVE CIRCUITS.

Always observe safety rules. Do not repair the equipment when the power is on; some equipment stays highly charged after the power is turned off. Always turn off the power before touching any circuits. Before making adjustments, remove all jewelry and be sure that your body is not grounded. Make adjustments with one hand and keep the other hand away from the equipment.

3. DO NOT SERVICE OR ADJUST ALONE.

Do not enter an area to service or adjust the equipment at any time unless another person who can give aid is present.

4. RESUSCITATION.

Anyone working with or near high voltages should know modern methods of resuscitation. These methods may be learned at the base hospital, at a local medical facility and/or in T.O. 31-1-141-01.

5. FIRST AID.

Seek medical help immediately after injury. Any injury, however slight, should be treated.

1-1

CHAPTER 1

SYSTEM FUNCTIONAL DESCRIPTION

1.1 TACAN NAVIGATIONAL SET (33-00-000).

1.1.1 TACAN Navigational Set Functional Description. (See Figure 1-1.) The following paragraphs provide an overall functional description on the operation of the TACAN Navigational Set. The ground station output is shown in Figure 1-2.

1.1.1.1 Transponder and Radio Frequency Amplifier (RFA). Incoming interrogation signals are processed through the RFA via the equipment cabinet antenna connector. The RFA contains the low pass filter, two directional/couplers, and a four-port circulator. The receiver port of the four-port circulator routes the interrogation signals into the radio transponder receiver. Upon decoding a valid interrogation, a transponder reply is generated and gated, following priority rules, with squitters, reference bursts and idents. These pulses are amplified to an RF level of 400w and routed to the RFA Amplifier where they are amplified to a level in excess of 3000w. This level is then applied to the transmit port of the four-port circulator through a low pass filter and two directional couples for transmission by the antenna.

1.1.1.2 Radio Frequency Monitor (Dual). The principle function of the radio frequency monitor is to continuously check the TACAN Navigational Set operation by measuring critical system parameters and checking them against predetermined fault limit values. Some fault limits are fixed while others are adjustable using the Software Control Program. Upon detecting a fault condition in the TACAN Navigational Set, the monitors may run fault diagnostic tests and gather data to determine the nature of the fault and subassemblies causing system failures. After completion of diagnostic tests, the monitors may elect to shut down the TACAN Navigational Set by disabling the transmitter. The monitors also serve as a communication and control link between the Personal Computer and the TACAN Navigational Set. Test interrogation samples are generated in each monitor and supplied to the transponder receiver by means of the directional coupler. Detected replies are fed to each monitor in the form of buffered detected replies for evaluation of all required parameters.

1.1.1.3 Personal Computer (PC). The Personal Computer communicates to both monitors via parallel data busses and communicates with the Remote Maintenance Work Center (RMWC) via existing voice telephone wire lines. Wire line communication is accomplished through modems resident in the computer and in the RMWC PC.

Transponder and amplifier fault signals are sent to the monitors via serial data interfaces, where they are processed with the monitor's own internal fault signals. The results of fault detection are then sent to the computer via the data bus.

1.1.1.4 Power Supply. The power supply operates on incoming AC power (120 or 240 VAC) and generates DC voltages for the transponder, amplifier, and monitors. The computer contains its own power supply and battery back-up.

1.1.1.5 Control Indicator. The TACAN transponder provides system status data and identification signals to the control indicator via telephone lines.

1.1.2 TACAN Navigational Set Theory of Operation. (Refer to T.O. 31R4-2FRN45-33SD-1 - 33-00-000.) The TACAN Navigational Set is a multi-channel transponder whose purpose is to provide bearing and distance information of up to 200 nautical miles (370.6 Km) (Line-Of-Site (LOS) distance) relative to the TACAN ground location. A TACAN transceiver installed in an aircraft transmits interrogation signals to the TACAN and then waits for a transmitted reply from the TACAN. The time between interrogation and reply is used to determine range.

Space modulation of the antenna pattern is used to determine aircraft bearing. Approximately 100 aircraft may use the TACAN at a time.

1.1.2.1 Cockpit Indicators. The airborne transceiver will display the channel, distance, and magnetic bearing information (see Figure 1-3).

1-2

Figure 1-1. Typical TACAN Facility and Equipment Locations.

1-3

Figure 1-2. Ground Station Output.

1-4

Figure 1-3. Typical Cockpit Indicators.

1.1.2.2 Channel Characteristics. There are 126 TACAN channels in each of two modes, "X" and "Y". Adjacent channel frequencies are in one MHz steps between 962 MHz and 1213 MHz. For each received frequency, there is an assigned transmit frequency 63 MHz away.

1.1.2.2.1 X mode. In this mode, the receive frequency range is between 1025 MHz and 1150 MHz, with the transmit frequency 63 MHz lower (between 962 MHz and 1024 MHz) for low band and 63 MHz higher (between 1151 and 1213 MHz) for high band.

1.1.2.2.2 Y mode. In the Y mode, the receive frequency range is between 1025 MHz and 1150 MHz, the transmit frequency being 63 MHz higher (between 1151 MHz and 1213 MHz) for low band and 63 MHz lower (between 1025 MHz and 1087 MHz) in the high band. Transmission in the high band requires a different antenna than for low band (refer to paragraph 1.1.2.5, TACAN Antenna Unit).

1.1.2.3 Interrogation. Interrogation signals to the navigational set are in the form of coded pairs of pulses (see Figure 1-4).

1.1.2.4 TACAN Distance (DME). Replies to interrogations (distance reply) are delayed 50 µsec in the transponder and are in the form of coded pairs (either X channel or Y channel) of pulses (see Figure 1-5). These distance reply pulses are inserted into a continuously transmitted pulse train (see Figure 1-6).

1.1.2.5 TACAN Antenna Unit. Electronic Scanned Phased Array provides all band, all terrain service.

1.1.2.6 TACAN Azimuth Signal. The TACAN azimuth is the bearing which an aircraft would have to fly to pass directly over the TACAN Navigational Set on the ground. The Antenna produces a rotating pattern by electronic means. The RF input from the TACAN is fed to 36 radiator columns. Each column is carefully modulated with a signal from the modulation generator to produce the same rotating RF space signal. (See Figure 1-7.) How the TACAN bearing is measured in an aircraft is described in the following paragraphs

1-5

Figure 1-4. Interrogation Reply Pulse Code.

Figure 1-5. Distance Reply Pulse Code.

1-6

Figure 1-6. TACAN Pulse Train.

1-7

Figure 1-7. Radiated Antenna Pattern.

1-8

1.1.2.6.1 Bearing Signal Transmission. An aircraft receives transmitted signals from a ground station that is radiating a rotating limacon antenna pattern. This signal is an RF carrier that is amplitude modulated by a sine wave whose frequency is the same as the antenna pattern rotation rate. The TACAN transceiver in an aircraft demodulates both the 15 Hz sine wave signal and the 135 Hz sine wave signal from the RF carrier. The transmitted signal from the TACAN is a train of pulses (see Figure 1-7) containing bearing reference bursts. The TACAN transceiver in the aircraft uses sine wave phase shift to measure and display aircraft bearing of zero to 360 degrees, relative to the TACAN locations on the ground.

1.1.2.6.2 Bearing Variable Signals. (See Figure 1-9.) The varying zero to 360 degree phase of the 15 Hz sine wave signal is directly related to the angular position of antenna. The varying zero to 360 degree phase of the 135 Hz sine wave signal is proportional to a zero to 40 degree segment of the antenna. There are nine angular segments of 40 degrees each. The 15 Hz signal is used to determine in which of these nine angular segments the aircraft is located. The 135 Hz signal is used to determine the angular position within a 40 degree segment.

Both the 15 Hz and the 135 Hz signals require a reference burst to indicate when the TACAN antenna is at a known angular position.

1.1.2.6.3 Bearing Reference Signals. The modulation generator produces triggers for the bearing reference bursts. The 15 Hz reference (north) burst consists of 12 pulse pairs spaced at 30 µsec intervals for X-mode channels and 13 single pulses spaced at 30 µsec intervals for Y-mode channels. The 135 Hz reference (auxiliary) burst consists of six pulse pairs spaced at 24 µsec intervals for X-mode channels and 13 single pulses spaced at 15 µsec intervals for Y-mode channels.

1.1.2.6.4 Bearing Measurement. When the peak of the cardiod pattern is pointing due east, the 15 Hz signal transmitted due south is passing through its sine wave axis from minimum to maximum voltage (see Figure 1-8).

The north reference burst is transmitted in all directions at one time, but only in the direction of due south does the 15 Hz reference burst occur simultaneously with the 15 Hz zero crossing. In each aircraft TACAN transponder, the received 15 Hz and 135 Hz signals are filtered and applied to phase shifters. The outputs of the filters are shifted in phase until the zero crossing from minimum to maximum coincides with the north reference burst and auxiliary reference burst. For an aircraft due south of the TACAN, the phase shift required would be zero, corresponding to a TACAN bearing of zero degrees (due north) (see Figure 1-8). For an aircraft due east of the TACAN, the phase would have to be shifted -270 degrees (to align the zero crossing of the north signal with the 15 Hz reference burst), resulting in a TACAN bearing indication of +270 degrees (due west) (see Figure 1-8).

The 15 Hz phase measurement is too coarse to provide a sufficiently accurate bearing measurement: The 135 Hz modulation and auxiliary reference bursts are used in the same fashion as the 15 Hz modulation and north bursts, with 9 times the accuracy. The 15 Hz reading is used to determine which 40 degree segment of the 135 Hz modulation is to be used.

1.1.2.6.5 Identification. In addition to the distance reply pulses, bearing information pulses, and squitter pulses, the ground station transmits an audio signal in international Morse code once every 30 seconds which enables the aircraft to identify the station. The signal consists of a train of 2700 pulse pairs per second, coded in such a way to produce 1350 Hz. The aircraft receiver decodes the pulses, which are transmitted as dots and dashes.

The duration of an identifying signal dot is 0.125 second; that of a dash is 0.375 second.

1.1.2.6.6 Squitter Pulses. The TACAN must maintain a constant duty cycle of 7200 pulses per second in order to maintain the amplitude modulated RF envelope. Squitter pulse pairs are noise-generated pulses that have no effect on distance reply pulses. Of the transmitted total of 7200 pulses per second, 1800 pulses per second are reference pulses for bearing: the remaining 2700 pulse pairs per second are distance reply and squitter pulses.

When the number of interrogations decrease, squitter pulses are increased to maintain the rate of 2700 pulse pairs per second (see Figure 1-9).

1.1.2.7 Pulse Priority. Certain TACAN signals have transmission priority over others in order to prevent interference. The signal priorities are azimuth bursts, identification, distance replies, and squitter pulses.

Transmission of distance reply pulses and squitter pulses are inhibited during the transmission of the 15 Hz reference burst, the 135 Hz reference burst, and the identification Morse code. The identification pulse cycle time may be up to five seconds long. A memory circuit in the aircraft receiver compensates for the time interval during which distance reply pulses are not transmitted.

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Figure 1-8. TACAN Bearing Measurement.

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Figure 1-9. Transmitted RF Carrier.

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1.2 TRANSPONDER GROUP (33-05-000).

1.2.1 Transponder Group Functional Description. (Refer to T.O. 31R4-2FRN45-2-33SD-1, 33-05-000.) The transponder group function is to receive, decode, process aircraft interrogations, and transmit coded replies containing azimuth, distance information, and station Morse code identity. Remote maintenance monitoring, fault diagnosing, isolating with display of probable faulted assemblies and transmitter control is provided. All remote communications are via standard telephone lines.

1.2.1.1 Receive/Transmitter Function. Aircraft interrogations received by the antenna are routed to the TACAN rack. The signal is routed through the RFA assembly and is applied to the transponder as INTERROGATION INPUT. The transponder decodes and processes incoming interrogations and produces the coded 400w RF DRIVE reply pulses to the RFA, which, in turn, amplifies the drive signal to 3 kW peak. The final 3 kW output is applied to the antenna (ANTENNA IN/OUT signal) through the RFA internal circulator and two directional couplers. Azimuth reference group pulses present in the transponder 400w RF DRIVE signal are synchronized to the NORTH TRIGGER and AUXILIARY TRIGGER pulses received from the Modulation Generator. Station Morse code identity is generated when a VOR KEY INPUT is received in the VORTAC configuration or independently in the event of loss of the VOR KEY INPUT signal or for a TACAN only configuration. The VOR KEY INPUT is routed to the transponder, which routes the signal to radio frequency monitors A and B. The primary monitor (normally A) generates a station Morse code identity, in response to the VOR KEY INPUT signal, which is sent to the transponder via the SERIAL DATA LINK. If the VOR KEY INPUT is not received within a 32 second period, the monitor will begin independent TACAN ident Morse code keying.

1.2.1.2 Monitoring Function. TACAN monitored and maintenance parameters are constantly being checked by monitors A and B. Each monitor independently generates MONITOR INTERROGATION test interrogations, which are coupled into the transponder INTERROGATION INPUT via the RFA. The transponder receives, decodes, and processes the test interrogation in addition to aircraft interrogations and produces coded reply pulses to the monitor and aircraft interrogations. A sample (RF FEEDBACK) of the transmitted signal is detected in the RFA and routed to the transponder where it is buffered and sent to the monitors as BUFFERED DETECTED REPLIES. The monitors then check this buffered detected reply signal for characteristics such as pulse spacing, reply delay, reply efficiency, pulse rate, identity, azimuth bursts, and pulse characteristics. The monitor also controls the overall system reply delay.

1.2.1.3 Transmitter Control Function. Control of TACAN system adjustments and independent monitor closed loop operational control is provided by only one monitor. Normally, monitor A is automatically the primary or controlling monitor. If a malfunction (not a parameter fault but an internal monitor failure) occurs in monitor A, or if power is off in monitor A, control is switched to monitor B. This is done in the transponder by selecting the serial data link and control signals from one monitor or the other, depending on the state of the CPU MAL signal from monitor A. The status of this line determines which is the controlling monitor. A subsequent malfunction of monitor B causes the transmitter to be removed from service.

1.2.1.4 Fault Status. The operational status of the individual assemblies in the RFA and transponder are sent to the monitors via the fault status signals. The monitors use these signals to help determine the faulted assemblies in the event of transponder or RFA malfunction. The monitors initiate fault diagnostic routines and report the analysis results to the Personal Computer via the communications interface data bus for further processing and display on the PC screen.

1.2.1.5 Personal Computer Function. All parameter data and TACAN system level adjustments are collected and transferred between the Personal Computer and the monitors via the communications data bus. Monitored and maintenance parameters are displayed and operator entries are made through the local and remote PCs.

The local PC is connected to the monitors via a cable to the TACAN. Communication to and from the remote PC is accomplished over a standard voice grade telephone line to a remote PC via modem. System parameters such as dead time gate width, receiver sensitivity, and reply efficiency settings are stored in the battery-backed RAM in the monitors. This allows the TACAN to remain in operation in the event the computer is removed from service.

A VOR interface for VORTAC configuration is also available in the computer to allow communication to and from both the TACAN and VOR.

1.2.1.6 Remote Control and Status. Remote control and status of the TACAN is provided to the Air Traffic Control (ATC) facility via the control indicator. NORMAL, ALARM, and BYPASS status information are displayed

1-12 and transmitter on/off control is available. Communications are provided using standard telephone lines or two-wire lines. Capability for additional expansion for remote control and status reporting by the transponder using fiber optics is provided by an optics interface in the transponder.

1.2.1.7 Power Supply. Power for the TACAN is provided by the power supply. The 120 VAC input is routed to the power supply through the EMI filter. The EMI filter prevents TACAN power supply generated electromagnetic noise from being conducted into the facility's power source. The supply converts the 120 VAC input to regulated +65 VDC for the transponder and RFA transmitter chain, unregulated +10 VDC, -17.5 VDC, and +17.5 VDC for the monitors and transponder post regulator supplies, and 120 VAC for the system fans. The transponder returns the +17.5 VDC back to the supply as the DC enable signal. The +17.5 VDC is returned through the transponder front panel power switch in order to provide electronic shutdown of the +65 VDC when the transponder is shut off.

Sample power supply voltages are sent to the computer for use in fault diagnosis and detection.

1.2.2 EMI Filter (33-05-100) Theory of Operation. (Refer to T.O. 31R4-2FRN45-2-33SD-1, 33-05-100.) The EMI filter circuit card protects the TACAN from interference due to other electronic equipment and lightning induced voltage on AC power lines. This circuit consists of the power filter circuit and the signal filter circuit.

1.2.2.1 Power Filter Circuit. Lightning protection of the 120 VAC main power line is provided by varistors VR1, VR2, and VR3. Varistor VR2 prevents voltage between the 120 VAC line and 120 VAC neutral line from exceeding 200v. Varistor VR1 prevents voltage between the 120 VAC line and chassis ground from exceeding 200v. VR3 protects the 120 VAC neutral line. If a voltage surge should occur on the power lines, the varistors clamp the input voltage into the rack at 200v, forcing the surge to dissipate to inductor L1. The 120 VAC accessory power lines are similarly protected by varistors VR4 through VR6 and inductor L2. Incoming RF noise on the 120 VAC line is filtered by the lowpass LC filter consisting of inductor L1 and capacitors C1 and C2. The two-pole LC filter has a bandpass at 40 kHz. The accessory power lines are filtered with identical filters.

Because the power line filters are discrete, the EMI filter assembly is itself shielded to keep out external RF noise.

1.2.2.2 Signal Filter Circuit. EMI protection is provided by physical shielding and filtering on all of the signal and power lines entering the TACAN rack. Signal lines are filtered by filter-connectors FL1 through FL12. The connectors are bulkhead mounted between the rack and the interior of the EMI assembly. This prevents RF noise on the signal lines from radiating from the rack. The individual filters prevent RF noise from conducting into the rack.

1.3 ANTENNA GROUP (33-15-000).

1.3.1 Functional Description: The antenna group consists of two units, the Antenna and Modulation Generator.

For a detailed description of each refer to T.O. 31R4-2FRN-41.

1.3.2 Antenna: The antenna is a cylindrical array consisting of 36 identical and equally spaced vertical radiating columns that provide for the transmission and reception of pulse-paired RF signals. The antenna consists of four basic circuits: 3-way power divider, azimuth feeds, vertical column arrays, and the monitor circuit consisting of 36 monitor diodes and multiplexer PC card. Transmission of pulse-paired RF is accomplished using 36 PIN diode modulators.

1.3.3 Modulation Generator: The Modulation Generator provides the 36 drive signals…