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Burst
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CK-8   AN/GRA-71
Electromechanical Burst Encoder

CK-8 is a coder/keyer, or burst encoder, for morse code signals, developed in the late 1950s by Stenographic Machines in Skokie (Illinois, USA), for the US Central Intelligence Agency (CIA). The device allows pre-recorded coded messages to be broadcast in morse code at very high speed, in order to be on the air a short as possible and minimise the risk of Radio Direction Finding (RDF). It is also known by its military designator GRA-71, and by the CIA abbreviation CO-CA-KE. 1

The CK-8 is a modular system that consists of a CO-8 alphabet encoder, a CO-3 dot-dash-space encoder (for recording plain morse signals), a CA-3 magnetic tape cartridge, and a KE-8 keyer.

The CO-8 (or the CO-3) was used to record a message onto one of the CA-3 magnetic tape cartridges. The tape cartridge was then rewound and attached to the KE-8 keyer, which in turn was connected to the radio transmitter. A spring mechanism was then released, causing the KE-8 to play back the pre-recorded message at high speed, reducing the risk of enemy interception.
  
CIA version of the CK-8 (GRA-71)

As the speed was too high for the human ear and brain to interpret the morse code signals, low-grade tactical messages were often sent unencrypted. High-grade field messages and espionage reports were commonly encrypted with a one-time pad cipher or with an external cipher machine. It was also possible to use the two letter-discs on the CO-8 as a simple Vigenère cipher system.

The CO-3 coder and CA-3 tape cartridge were initially developed for use with the AS-3 spy radio set, which had a built-in keyer. The items – complemented by an external KE-8 keyer – were later re-released as the CK-8 coder/keyer set.

One of the first radios to be retro-fitted with a socket for connection of the CK-8, was the RS-1. It was later also used with other CIA radio sets, but also with European stay-behind radio sets. Around 1970, a motorised version of the KE-8 was introduced. It was known as KE/M-8 and was first used with the CIA's TAR-224 radio set.
  
AN/GRA-71 with all items unpacked

The military version of the CK-8, usually supplied in black enclosures, was known as AN/GRA-71 and as NSN 5820-00-056-6856. It came in a waterproof container that doubled as an interface between the keyer and the radio. The CK-8 (GRA-71) set was in production until at least 1979.

  1. Coder, Cartridge, Keyer.

Stay-behind version of the GRA-71 burst encoder
GRA-71 closed container
GRA-71 with its lid taken off
GRA-71 with all items stored inside the container
Protective caps removed from the connectors
Complete GRA-71 with all modules outside the container
Keyer Adapter
GRA-71 with Keyer attached to the T-784 transmitter
A
×
A
1 / 8
Stay-behind version of the GRA-71 burst encoder
A
2 / 8
GRA-71 closed container
A
3 / 8
GRA-71 with its lid taken off
A
4 / 8
GRA-71 with all items stored inside the container
A
5 / 8
Protective caps removed from the connectors
A
6 / 8
Complete GRA-71 with all modules outside the container
A
7 / 8
Keyer Adapter
A
8 / 8
GRA-71 with Keyer attached to the T-784 transmitter

Versions
Operation
Messages are recorded onto CA-3 magnetic tapes, using one of the two supplied coders – CO-3 and CO-8 – much like using a domestic tape recorder. One coder (CO-8) has a disc with the 26 letters of the alphabet. It allows letters to be recorded directly in morse code. Alternatively, the CO-3 dash-dot coder can be used, allowing any morse character to be composed manually, including numbers and punctuation marks. Once the recording is complete, the KE-8 keyer is connected to the transmitter in order to play back the message at the high speed of ~ 300 wpm.

AN/GRA-71 Block Diagram

The diagram above shows the flow of information when using the CK-8 (GRA-71). At the left are the two possible routes to choose from. Whether the user selects the CO-3 dot-dash coder or the CO-8 alphabet coder, the messages are always stored as a sequence of (morse code) dots and dashes onto a CA-3 tape cartridge. The tape has two separate tracks: the upper track is used to record the dashes, whilst the lower track is used for recording the dots, as illustrated below.

AN/GRA-71 Tape Layout

In the above example, the text NOW IS THE TIME (in morse: -· --- ·--    ·· ···    - ···· ·    - ·· -- ·) is recorded onto a tape cartridge. The coders are mechanically constructed in such a way that an accurate timing is guaranteed for the dashes, dots and the spaces between letters and words.

Once the message is complete, the cartridge is removed from the coder and attached the the actual Keyer (KE-8). As the keyer can not be connected to old valve-based transmitters, the KA-3 Keyer Adapter had to be used as an interface for the high anode voltages of the valves. Later transistor-based transmitters, like the PRC-64A, could be connected directly to the KE-8 keyer.

Rewinding the tape
After recording a message, and detaching the CA-3 cartridge from the coder, a spring-loaded mechanism inside the tape cartridge ensures that the tape will automatically return to the staring position. This means that there is no need to rewind the tape manually.

Erasing the tape
The Keyer can also be used to erase a Tape Cartridge by winding-up the mechanism, attaching a pre-recorded tape, sliding the ERASE switch to the upper position (and keeping it in that position) whilst sliding the ON/OFF switch to the ON position. The ERASE switch will now be locked-in.

Identification
At the rear of the Keyer is a switch marked IDY (identification). When engaged, it uses the dot-channel of the Keyer to send a continuous sequence of dots at a rate of 300 wpm.

Compatible radios
RS-1 (AN/GRC109)
Automatic CIA agent radio set
AN/PRC-64 and Delco 5300
RS-59 modular spy radio station
German spy set SP-15
Dutch version of the SP-15 with synthesizer
QRC-222 suitcase spy radio set (1964)
German spy set SP-20
TAR-224A spy radio set
Most solid state radios can be used in combination with the CK-8 (GRA-71), although in some cases a special cable is required. Apart from the radios listed below, the CK-8 (GRA-71) was used with a variety of Cold War spy radio sets, both in the USA and in Europe. In The Netherlands, it was used by Korps Commando Troepen (KCT) – the Dutch Special Forces – in combination with the TRC-77 radio. This radio was also very popular with the Special Forces in Vietnam at the time.

CIA version   CK-8
CK-8 was developed for CIA radios, but was also used by European stay-behind organisations. It consists of the same parts as the military version, but the storage container — and hence the MX-4498 Keyer Adapter — is omitted. In this case, the radio should take care of any level conversion.

The image on the right shows (from left to right) the dot-dash morse encoder CO-3A (also known as the MX-4495), the CO/B-8 alphabet encoder (also known as the MX-4496), and the KE-8E keyer (also known as the KY-468). The latter is used for playing back a recorded message. The matching tape cartridge is not shown here.

A detailed description of each item is provided below, in the section 'Parts'. A suitable cable for connecting the KE-8E keyer to the FSS-7 stay-behind set, is shown at the bottom of the page. This cable was part of an early FSS-7 setup.
  
Stay-behind version of the GRA-71 burst encoder

Please note that in some cases, the black variant of the device was supplied with stay-behind radio sets. Apart from the colour, the items are functionally identical. In Europe, the stay-behind version of the CK-8 was later succeeded by electronic burst transmitters, like Speicher and MMP.

Parts   CK-8
CA-3 tape cartridge
CO-3 morse dot-dash coder
CO-8 morse alphabet coder
KE-8 morse keyer, driven by spring-motor
KE/M-8 morse keyer, driven by electric motor
Tape cartridge   CA-3
Messages – preferably encrypted – were recorded as morse code symbols on to standard magnetic (ferro) audio tape, similar to the tape used with domestic audio recorders. Each cartridge holds 12.5 feet of '428' industrial grade recording tape – manufactured by 3M – which is sufficient for holding 150 five-letter groups (words).

The dots and dashes of the morse code are recorded as a series of pulses in two individual tracks. When recording, the tape is advanced automatically by the coder.

  
CA/A-3B tape cartridge

Dot-dash coder   CO-3
The CO-3 is the oldest of the two coders. It has only three buttons: one for dots, one for dashes and one for spaces, and allows any possible morse character to be composed freely.

This coder requires the operator to be familiar with the morse alphabet and was often preferred as it was the lighter of the two. Like the CO-8, the CO-3 is a passive device that does not require an external electrical power source. Pushing down a button generates just enough electric energy to store the data onto the tape.

  
CO-3A coder (open)

Alphabet coder   CO-8
The CO-8 alphabet coder allows any character of the Latin alphabet to be recorded onto the tape cartridge in morse code. It can be used by operators without knowledge of morse code.

When operating the lever, a built-in miniature power generator provides the electric energy to operate the device. Numbers (0-9) are recorded as letters (A-J or Q-Z). Spaces can be inserted by pressing the word-space button.

  
CO-8 alphabet coder

Wind-up keyer   KE-8
KE-8 was the standard morse keyer of the CK-8 set. It is driven by a spring-loaded mechanism, or spring-motor, that must be wound-up before each transmission, with the foldable crank at the top. It is basically the same device as the KE-8B supplied with the military AN/GRA-71.

The image on the right shows a KE-8 with its hinged lid open. A later version uses an electric motor (see below).
  
KE-8 keyer with wind-up mechanism

Motorised keyer   KE/M-8
The KE/M-8 is basically the motor-driven version of the KE-8 featured above. It has the same outer dimensions, but is powered by an external 12V DC source – typically provided by the radio to which it is connected – instead of a wind-up clockwork mechanism.

The image on the right shows a typical KE/M-8 as it was found with a TAR-224 spy radio set. It was introduced by the CIA in the late 1970s.
  
KE/M-8 keyer seen from the front

Stay-behind version of the GRA-71 burst encoder
KE/M-8 keyer seen from the front
KE/M-8 keyer seen from the rear
Controls
KE-8 wind-up keyer (right) and motor-driven KE/M-8 (left)
KE-8 wind-up keyer (right) and motor-driven KE/M-8 (left)
B
×
B
1 / 6
Stay-behind version of the GRA-71 burst encoder
B
2 / 6
KE/M-8 keyer seen from the front
B
3 / 6
KE/M-8 keyer seen from the rear
B
4 / 6
Controls
B
5 / 6
KE-8 wind-up keyer (right) and motor-driven KE/M-8 (left)
B
6 / 6
KE-8 wind-up keyer (right) and motor-driven KE/M-8 (left)

Military version   GRA-71
The military version of the device was commonly painted black, and was supplied in the water tight contains shown below, which also acts as the interface between the device and the radio. The other components are functionally identical to those of the standard (grey) CIA version.

Each items has its own slot – which is read on the inside – so that the container can easily be checked for completeness. All items can be removed, with the exception of the KA-3 keyer adapter, which is an integral part of the case.

The keyer-adapter (KA-3) has two cables: one for connection to the radio, and one for keyer. They are shown here in their storage position. The GRA-71 was used in combination with a variety of special forces and stay-behind radio sets, including the RS-1 (GRC-109), the PRC-64A, the PRC-74A, the RS-59 and the SP-15.
  
All items packed inside the container (lid removed)

Burst encoders like the GRA-71 were very popular with the American Special Forces (SF) during the Vietnam War, as they drastically shortened the time needed to occupy the limited frequency space that was available at the time. The CIA used burst encoders also to limit the risk of interception and Direction Finding (DF) by the enemy. The GRA-71 was used well into the 1970s when it was replaced by digital systems. The price of a single GRA-71 unit was US$ 759.14 [2].

GRA-71 closed container
GRA-71 with its lid taken off
GRA-71 with all items stored inside the container
Protective caps removed from the connectors
Complete GRA-71 with all modules outside the container
Clearly showing the two cables of the Keyer Adapter
Keyer Adapter
GRA-71 with Keyer attached to the T-784 transmitter
C
×
C
1 / 8
GRA-71 closed container
C
2 / 8
GRA-71 with its lid taken off
C
3 / 8
GRA-71 with all items stored inside the container
C
4 / 8
Protective caps removed from the connectors
C
5 / 8
Complete GRA-71 with all modules outside the container
C
6 / 8
Clearly showing the two cables of the Keyer Adapter
C
7 / 8
Keyer Adapter
C
8 / 8
GRA-71 with Keyer attached to the T-784 transmitter




Click to see more

Parts   GRA-71
CA-3B Tape Cartridge
CO-3B Dot-Dash Coder
CO/B-8 Alphabete Coder
KE-8B Keyer
KA-3 Keyer Adapter
Alternative alphabet disk
Camel hair cleaning brush
Operating and Maintenance Manuals
Tape cartridge   CA-3B, MA-9

Messages – preferably encrypted – were recorded as morse code symbols on to standard magnetic (ferro) audio tape, similar to the tape used with domestic audio recorders. Each cartridge holds 12.5 feet of '428' industrial grade recording tape – manufactured by 3M – which is sufficient for holding 150 five-letter groups (words).

The dots and dashes of the morse code are recorded as a series of pulses in two individual tracks. When recording, the tape is advanced automatically by the coder.

  
CA-3B Tape Cartridge
Dot-dash coder   CO-3B, MX-4495
The CO-3B coder was supplied as an alternative to the heavier CO/B-8 alphabet coder (see below). It had only three buttons: one for dots, one for dashes and one for spaces, and allowed any possible morse character to be composed.

This coder required the operator to be familiar with the morse alphabet and was often preferred as it was the lighter of the two. Like the CO/B-8, the CO-3B is a passive device that does not require an external electrical power source. Pushing down a button produces just enough electric energy to store the data onto the tape.

  
CO-3B Dot-dash Coder

Alphabet coder   CO/B-8, MX-4496
The CO-8 alphabet coder allows any character of the Latin alphabet to be recorded onto the tape cartridge in morse code. It can be used by operators without knowledge of morse code.

When operating the lever, a built-in miniature power generator provides the electric energy to operate the device. Numbers (0-9) are recorded as letters (A-J or Q-Z). Spaces can be inserted by pressing the word-space button.
  
CO/B-8 Alphabet Coder

Alternative index disk   for CO/B-8
The CO/B-8 coder was supplied with two alphabet discs: one disc with the letters A-Z in reverse order and an inner ring (in red) that contained the letters A-Z in the correct order. The image on the right shows this disc mounted on the CO/B-8 coder. At the reverse side, this disc contains the alphabet in reverse order (Z-A).

A spare disc was supplied with the letters (A-Z) in the correct order, corresponding directly with the morse characters A-Z. The numbers (0-9) are always sent as letters (A-J or Q-Z).

  
Alternative alphabet disk

Keyer   KE-8, KE-8B, KY-468
KE-8, also known as KY468, is the actual keyer, and replaces the morse key of the radio to which it is connected. It plays back the tape cartridge using an internal spring-motor, that must be wound-up manually before each transmission.

It can be connected directly to a transistorised transmitter, via the 7-pin Winchester socket at the rear and is powered directly by a 12V DC source sypplied by the transmitter. When using the keyer with a valve-based transmitter, the KA-3 keyer adapter (see below) should be used.
  
KE-8B Keyer

Keyer Adapter   KA-3, MX-4498
When using the KE-8 keyer with a valve-based transmitter, such as the T-784 of the RS-1 spy set (AN/GRC-109), the KA-3 should be used as an interface. It converts the low-voltage signals to the anode voltage of the transmitter. It is not required for transistorised transmitters.

An R/C timing circuit enables the oscillator of the T-784 transmitter for the duration of the transmission. Once the last character has been sent, the oscillator is disabled after ~ 1 second. The device also converts the filament voltage of 6.3V into 12V DC for the KE-8 keyer circuits.

  
Keyer Adapter

Soft cleaning brush
A soft camel hair cleaning bush is supplied to allow the contact and the mechanical parts to be cleaned regularly. It can be stowed in a circular slot between the alphabet coder and the keyer.

The brush itself works like a lipstick; take off the cover and rotate the shaft to reveal the brush. Rotate backwards to retract the brush again.
  
Camel hair cleaning brush

Manuals
Two manuals were available for the GRA-71: a small instruction manual – TM 11-5835-224-12 [B], and a larger Depot Maintenance Manual – TM 11-5835-224-35 [C]. Both manuals are shown in the image on the right, and are available for download below.

 Instruction manual
 Maintenance manual

  
GRA-71 Manuals

Closed Tape Cartridge
Two CA-3B Tape Cartridges
CA-3B Tape Cartridge
Close-up of the opened Tape Cartridge
Side-view of the opened Tape Cartridge
Close-up of the tape guides
Tape transport mechanism
CO-3B dot-dash coder with tape cartridge attached
CO/B-8 Alphabet Coder
Attaching the tape cartridge to the Alphabet Coder
Alphabet Coder with Tape Cartridge attached
Handle raised
Operating the handle
Pushing the handle down
Close-up of the recording head
Adding a word-spacing
CO-3B Dot-dash Coder
Dot-dash coder in operation
Compact dot-dash coder
Opening the dot-dash coder
Placing the tape cartridge
Attaching the tape cartridge
Close-up of the tape cartridge mounted on the CO-3B coder
Closed Keyer with crank in storage position
KE-8B Keyer
Keyer rear panel
Operating the crank to wind-up the mechanism
Placing the Tape Cartridge on the Keyer
Attaching the tape cartridge
Keyer with Tape Cartridge attached
Putting the crank in its storage position
Keyer Adapter
Keyer Adapter: top view of the empty container
Close-up of the Keyer Adapter
Keyer (with tape cartridge) connected to the Keyer Adapter
GRA-71 with Keyer attached to the T-784 transmitter
Closed cleaning brush
Camel hair cleaning brush
Using the cleaning brush
GRA-71 Manuals
D
×
D
1 / 40
Closed Tape Cartridge
D
2 / 40
Two CA-3B Tape Cartridges
D
3 / 40
CA-3B Tape Cartridge
D
4 / 40
Close-up of the opened Tape Cartridge
D
5 / 40
Side-view of the opened Tape Cartridge
D
6 / 40
Close-up of the tape guides
D
7 / 40
Tape transport mechanism
D
8 / 40
CO-3B dot-dash coder with tape cartridge attached
D
9 / 40
CO/B-8 Alphabet Coder
D
10 / 40
Attaching the tape cartridge to the Alphabet Coder
D
11 / 40
Alphabet Coder with Tape Cartridge attached
D
12 / 40
Handle raised
D
13 / 40
Operating the handle
D
14 / 40
Pushing the handle down
D
15 / 40
Close-up of the recording head
D
16 / 40
Adding a word-spacing
D
17 / 40
CO-3B Dot-dash Coder
D
18 / 40
Dot-dash coder in operation
D
19 / 40
Compact dot-dash coder
D
20 / 40
Opening the dot-dash coder
D
21 / 40
Placing the tape cartridge
D
22 / 40
Attaching the tape cartridge
D
23 / 40
Close-up of the tape cartridge mounted on the CO-3B coder
D
24 / 40
Closed Keyer with crank in storage position
D
25 / 40
KE-8B Keyer
D
26 / 40
Keyer rear panel
D
27 / 40
Operating the crank to wind-up the mechanism
D
28 / 40
Placing the Tape Cartridge on the Keyer
D
29 / 40
Attaching the tape cartridge
D
30 / 40
Keyer with Tape Cartridge attached
D
31 / 40
Putting the crank in its storage position
D
32 / 40
Keyer Adapter
D
33 / 40
Keyer Adapter: top view of the empty container
D
34 / 40
Close-up of the Keyer Adapter
D
35 / 40
Keyer (with tape cartridge) connected to the Keyer Adapter
D
36 / 40
GRA-71 with Keyer attached to the T-784 transmitter
D
37 / 40
Closed cleaning brush
D
38 / 40
Camel hair cleaning brush
D
39 / 40
Using the cleaning brush
D
40 / 40
GRA-71 Manuals

Circuit diagram
Below is the circuit diagram of the CO-3 and CO-8 coders. At the left is the miniature signal generator (G1). In the CO-3 it is driven by pressing the dash and dot buttons. The same buttons also operate the two switches (S1 and S2), which in turn feed the signal from the generator (G1) to the recording heads (H1a and H1b). The signal is then recorded as a pulse onto the tape.


The circuit diagram of the CO-8 coder is identical, but the generator (G1) is operated by the U-shaped lever, and the switches (S1 and S2) are operated by a coded disc inside the device. The circuit diagram of the keyer can be found on the last page of the maintenance manual [C].


Connections
The KE-8 keyer has a 7-pin Winchester M-series socket [1] at the rear, allowing the unit to be connected directly to a transistorized (solid-state) transmitter. The transmitter needs to supply 12V DC for the electronic circuits inside the Keyer. The pin-out of the socket is as follows:

KE-8B pinout, looking into the Winchester M7S socket.

J2 - Keyer socket (M7S)

Note that the SIGNAL lines are galvanically isolated from the 12V circuitry. In most cases, a purpose-built cable will be needed between the Keyer and the transmitter. When used in combination with a valve-based transmitter, such as the T-784 of the RS-1 spy set (AN/GRC-109), The Keyer Adapter (KA-3) (part of the GRA-71 container) is used as an interface. A fixed cable on the KA-3 (marked TRANS) has an M10P connector at the end, with this pinout:

KA-3 pinout of J1, looking into the Winchester M10S socket on the transmitter.

J1 - Transmitter socket (M10S)

The 6.3V filament power from the transmitter (AC or DC) is supplied by the transmitter on pins H (6.3V) and J (GND) of J1. This voltage is converted by the KA-3 into 12V DC that is available on pins H (+12V) and C (-12V) of J2. Pins C and F of J1 are both connected to the screen grid of the PA valve of the transmitter, which is keyed via the cathode of the PA valve using the signal at pin B. Pin A provides a timed signal to the cathode of the oscillator valve, keeping the oscillator ON whilst sending a burst message. The HT voltage (B+) is received from the transmitter on pin E.

SP-15 cable
When the KE-8B keyer was used in combination with the SP-15 spy radio set, or more precisely, the FSS-7 stay behind radio set, it could be connected directly to the IF-7 interface of the FSS-7, without using the KA-3 keyer adapter. This is possible because the IF-7 supplies the necessary -12V DC voltage for the KE-8B. The cable between the KE-8B and the IF-7 is wired as follows:



 More about the FSS-7 spy radio set


QRC-222 cable
When the KE-8 keyer was used in combination with the QRC-222 radio set, it could be connected directly to the transceiver, without the need to connect the KA-3 keyer adapter. This is possible because the RS-8 (QRC-222) supplies +12V DC through the cable, shown in the diagram below.



 More about the QRC-222 spy radio set



Designators
CIA US Army Description    
CK-8 AN/GRA-71 Complete set    
CO/B-8 MX-4496/GRA-71 Alphabet Coder    
CO-3B MX-4495/GRA-71 Dot-dash Coder    
CA-3B MA-9/GRA-71 Tape Cartridge    
KE-8B KY-468/GRA-71 Keyer    
KE/M-8 ? Keyer with electromotor    
KA-3 MX-4498/GRA-71 Keyer Adapter    
Nomenclature
The burst encoder/keyer kit described on this page is known under the following names:

  • CK-8
    CIA designator
  • GRA/71
    Military designator
  • AN/GRA-71
    Military designator
  • CO-CA-KE
    Coder, Cartridge, Keyer (CIA designator)
  • NSN 5820-00-056-6856
    Military designator
Literature
  1. CIA, Trip Report - Magnetic Coder/Keyer, CK-8
    The Files - RD-151, T.O. 1, 31 December 1958. 1

  2. CIA, Trip Report - Coder/Keyer, CK-8
    The Files - RD-151, T.O. 1, 31 March 1959. 1

  3. CIA, Minutes, Eqipment Board 4 May 1960
    CK-8 demonstration, 10 May 1960. 1

  4. CIA, Monthly Report, 1 September 1961 - 30 September 1961
    Research and Development Branch Engineering Staff. September 1961. 1

  5. CIA, Equipment Board Minutes 7-62
    Unit cost, July 1962. 1

  6. CIA, KE-8 keyers
    Memorandum, 5 September 1962. 1

  7. CIA, Telecon Report - Keying Circuitry
    The Files - Contract RD-151, Task Order 1, 14 April 1959. 1

  8. CIA, Handout concerning the Equipment Board meeting of 6 March 1973
    2 March 1973. 1

  9. CIA, Minutes of the Equipment Board Meeting of 6 March 1973
    9 March 1973. 1
  1. Declassified (sanitised) by CIA.

Documentation
  1. CO-8 morse code writer, CA-3 tape cartridge, KE-8 keyer
    CIA, Date unknown but probably 1960. 1

  2. AN/GRA-71, Operator and Organizational Maintenance Manual
    US Army, TM 11-5835-224-12. Reprint, June 1964 (digital copy).

  3. AN/GRA-71, Depot Maintenance Manual / Repair Manual
    US Army, TM 11-5835-224-35. 25 July 1969. 2
  1. Declassified (sanitised) by CIA.
  2. Supersedes TM 11-5835-224-45, 15 February 1967, and TM 11-5835-224-45P, 24 June 1966.

References
  1. US Army, AN/GRA-71, Operator and Organizational Maintenance Manual
    TM 11-5835-224-12. Reprint, June 1964 (digital copy).

  2. US Army, AN/GRA-71, Depot Maintenance Manual / Repair Manual
    TM 11-5835-224-35. 25 July 1969. 1

  3. Winchester, M-Series connectors - datasheet
    Date unknown. Retrieved December 2012.

  4. Peter McCollum, GRA-71 Burst-Coder
    Website 1999-2012. Retrieved December 2012.
  1. Supersedes TM 11-5835-224-45, 15 February 1967, and TM 11-5835-224-45P, 24 June 1966.

Further information
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Crypto Museum. Created: Monday 03 August 2009. Last changed: Saturday, 14 November 2020 - 11:24 CET.
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