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Cold War
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RS-1   AN/GRC-109
Modular watertight spy radio set

RS-1 is a watertight modular valve-based spy radio set, developed at the start of the Cold War – around 1948 – by the US Central Intelligence Agency (CIA) and Radio Development and Research Corporation (RDR). The first 3-piece units were fielded around 1950 and were used for CIA field agent communication and for Stay-Behind Organisations (SBOs) in Europe. From 1961 onwards, the set was also used by the US Army, where it was known by the designator AN/GRC-109 [1].

The RS-1 consists of separate modules that are each housed in a water-tight container, allowing the radio to be stored under harsh conditions for an extended period of time. Each box has a lid with 4 screws at the corners and a rubber gasket to protect it against water. The set is heavy and can withstand air droppings and being buried in the ground; ideal for stay-behind organisations.

An example of a complete radio station is shown in the image on the right. It consists of a T-784 transmitter, a R-1004 receiver and a PP-2684 (or the small PP-2685) power supply unit (PSU).
  
The complete RS-1 set: receiver, PSU and transmitter

The CIA used the RS-1 spy set in many countries around the world, such as South-East Asia, some countries behind the former Iron Curtain (East-Europe), Vietnam, Tibet and Cuba. With the CIA it lasted for nearly 15 years because of its proven track record and reliability. The Army used it even longer, despite the fact that newer and lighter spy sets had meanwhile become available.

Development of the RS-1 started in 1948 by the CIA and Radio Development and Research Corp. (RDR). It is believed that the first prototypes and a small production batch were manufactured by RDR around 1950. The bulk production was then taken over by Admiral Corp. The version with clip-on case lids, was manufactured by Oklahoma Aerotronics, Inc. The RS-1 was in production until 1964, but was used for several years after that, in some cases well into the 1970s. The set was succeeded by the RS-6, which was much smaller and far less heavy, but was not watertight.

The three units packed in water-tight containters
The screws at the corners of the containers
The complete RS-1 set: receiver, PSU and transmitter
The complete RS-1 set: receiver, PSU and transmitter
The receiver
The crystal socket on the receiver
The transmitter
Close-up of the morse key on the transmitter and the socket for the external keyer
A
×
A
1 / 8
The three units packed in water-tight containters
A
2 / 8
The screws at the corners of the containers
A
3 / 8
The complete RS-1 set: receiver, PSU and transmitter
A
4 / 8
The complete RS-1 set: receiver, PSU and transmitter
A
5 / 8
The receiver
A
6 / 8
The crystal socket on the receiver
A
7 / 8
The transmitter
A
8 / 8
Close-up of the morse key on the transmitter and the socket for the external keyer

Parts
Receiver RR-2 (R-1004)
RX
Transmitter RT-3 (T-784)
TX
Power supply unit, inverter and battery charger RP-1 (PP-2684)
Power supply unit RP-2 (PP-2685)
Burst encoder CK-8 (GRA-71)
Maintenance kit with accessories and spares
Receiver RR-2   R-1004
RR-2 is a single-conversion super heterodyne receiver with 6 valves: RF pre-amplifier (1T4), local oscillator/mixer (1L6), 2 x IF amplifiers (1T4), AF amplifier (1U5) and a BFO (1T4). The intermediate frequency (IF) is at 455 kHz. The receiver can be crystal or VFO operated.

The image on the right shows an RR-2B receiver, which covers 3 to 24 MHz in 3 bands:
  • 3 - 6 MHz
  • 6 - 12 MHz
  • 12 - 24 MHz
  
Click to see more

Transmitter RT-3   T-784
The transmitter is only suitable for CW (morse) and covers 3 to 22 MHz in 4 bands. It has two valves: an 6AC7 for the crystal oscillator and a 2E26 for the RF power amplifier. The output power is 12-15W (at 3-15MHz) and 10-12W (at 15-22MHz).

Some transmitters have been modified with a socket for connection of a burst encoder.
  
Click to see more

Power Supply Unit RP-1   PP-2684
The RP-1 is the larger of the two power supply units. It can power the RS-1 radio station from virtually any AC mains voltage in the world. In addition it contains a built-in power invertor, allowing the radio to be powered by a 6V DC source such as a car battery. It can also be used to recharge the 6V battery from the mains.

The RS-1 can also be used in combination with the SSP-11 hand-crank generator, which is a modified version of the GN-58.

  
RP-1 power supply unit (PP-2684)

Power Supply Unit RP-2   PP-2685
The smaller RP-2 PSU has the same size as the RX and TX units. It is suitable for connection to the mains only and does not have a DC or battery input.

Note that the mains plug is made of rubber, so that the two contact pins can be pressed together in order to fit a variety of mains sockets.
  
Click to see more

Burst encoder CK-8   GRA-71
In order to avoid detection by enemy eavesdroppers, it was necessary to be on the air as short as possible. The Army version of the RS-1 was therefore modified to allow an AN/GRA-71 burst encoder to be connected.

A limited number of CIA sets was also modified for use with this burst encoder and the RT-3 transmitter was then renamed RT/D-3.

 More information
  
GRA-71 with Keyer attached to the T-784 transmitter

Spares
Some RS-1 sets came with a rectangular container with accessories and spares, that is shown in the image on the right. The container has a watertight lid that is held in place by two spring-loaded clip locks at the short sides.   
Maintenance kit (open)

With watertight lid in place
RP-1 power supply unit (PP-2684)
Serial number tag
Close-up of the RP-2 PSU
The small RP-2 power supply unit
RP-2 with original mains cable rolled up
Close-up of the RP-2 PSU
Rubber 'configurable' mains power plug
Maintenance kit
Maintenance kit (open)
B
×
B
1 / 10
With watertight lid in place
B
2 / 10
RP-1 power supply unit (PP-2684)
B
3 / 10
Serial number tag
B
4 / 10
Close-up of the RP-2 PSU
B
5 / 10
The small RP-2 power supply unit
B
6 / 10
RP-2 with original mains cable rolled up
B
7 / 10
Close-up of the RP-2 PSU
B
8 / 10
Rubber 'configurable' mains power plug
B
9 / 10
Maintenance kit
B
10 / 10
Maintenance kit (open)

Connections
Burst encoder
When using the RS-1 in combination with the AN/GRA-71 burst encoder described above, the encoder has to be connected to the special socket, marked KEYER, just above the internal morse key of the T-784 transmitter. This socket is only available on modified T-784 transmitters.

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

Keyer socket (M10S)

The actual burst encoder of the GRA-71, the so-called KE-8B Keyer, can be connected to the T-784 transmitter, using the KA-3 Keyer Adapter as an interface. It converts the low-voltage signals of the transistor-based GRA-71 into the high-voltage levels of the valve-based T-784.

The transmitter is modulated by switching the Anode of the Power Amplifier (PA) valve in the rithm of the morse data. During transmission, the transmitter's oscillator is kept running by an R/C timing circuit inside the Keyer Adapter. The oscillator is turned off automatically approx. one second after the last (morse) character has been sent by the burst encoder. The Keyer Adapter also contains a stabilizer for the PA screen grid voltage. Please refer to the circuit diagram of the Keyer Adapter in the GRA-71 Depot Maintenance Manual for further information [C].

Shorting plug that must be inserted into J1 if no burst keyer is present.

Shorting connector

If the T-784 transmitter has a socket for an external keyer and no keyer is connected, a shorting plug should be inserted into socket J1. Without this shorting plug, the transmitter will not work. The diagram above shows the wiring of the shorting plug. There are two bridges: A, B, L and E, K.


Designators
Originally, the set was called RS-1 by the CIA. Around 1961 the US Army adopted the set for their special forces (DF) and designated it AN/GRC-109.

CIA model Army designator Description
RS-1 AN/GRC-109 Complete radio set
RT-3 T784/GRC-109 Transmitter
RR-2 R1004/GRC-109 Receiver
RP-1 PP-2684/GRC-109 Large PSU
RP-2 PP-2685/GRC-109 Small PSU
CK-8 AN/GRA71 Burst Encoder (optional)
SSP-11 GN-58 (mod) Hand-crank generator
unmarked CY-1321/GRC-109 Maintenance kit
Specifications
  • Type
    Agent radio set
  • Model
    RS-1
  • Designator
    AN/GRC-109
  • Purpose
    Agent communication, Stay-Behind
  • Period
    Cold War
  • Development
    1948
  • Developer
    CIA, Radio Development and Research Corpration (RDR)
  • Production
    1950-1964
  • Manufacturers
    Radio Development and Research Corpration (RDR)
    Admiral Corporation
    Oklahoma Aerotronics, Inc.
  • Users
    CIA field agents (12-15 years)
    US Army (15+ years)
    Stay-Behind Organisations
Receiver   RR-2
  • Model
    RR-2
  • Designator
    R-1004
  • Frequency
    3-24 MHz
  • Bands
    3 (3-6 MHz, 6-12 MHz, 12-24 MHz)
  • IF
    455 kHz
  • Circuits
    RF pre-amplifier (1T4), Local oscillator/mixer (1L6),
    2 x IF amplifier (1T4), AF amplifier (1U5), BFO (1T4)
  • Valves
    1T4 (4x), 1L6, 1U5
Transmitter   RT-3
  • Model
    RT-3
  • Designator
    T-378
  • Frequency
    3-22 MHz
  • Bands
    4
  • Modulation
    CW
  • Output
    12-15W (3-15 MHz), 10-12W (15-22 MHz)
  • Circuits
    Crystal oscillator (6AC7), RF power amplifier (2E26)
  • Valves
    6AC7, 2E26
  • Option
    Socket for connection of CK-8 burst encoder
Power supply unit 1
  • Model
    PP-1
  • Designator
    PP-2684
  • Mains
    AC
  • Battery
    6V DC
Power supply unit 2
  • Model
    PP-2
  • Designator
    PP-2685
  • Mains
    AC
  • Battery
    no
Burst encoder
Documentation
  1. Operator Manual — Radio Set AN/GRC-109
    Re-typeset and fully searchable via OCR (author unknown).
    TM 11-5820-474-14. US Army. 18 May 1962.
     Original manual, scanned by Google

  2. Operator Manual — Coder-Burst Transmission Group AN/GRA-71
    TM 11-5835-224-12. US Army.
     More

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

References
  1. Louis Meulstee, Wireless for the Warrior, volume 4
    ISBN 0952063-36-0, September 2004
Further information
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Crypto Museum. Created: Thursday 01 October 2009. Last changed: Tuesday, 19 April 2022 - 07:39 CET.
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