Spy radio
Burst encoders
• • • Donate • • •
   Logo (click for homepage)
RS-1   AN/GRC-109
Spy radio set

The RS-1 is a robust valve-based spy radio set that was developed in the USA by the CIA and Radio Development and Research Corporation at the start of the Cold War, probably around 1948. The first units appeared in the field around 1950. They were intended for use by CIA field agents and for stay-behind organisations. The US Army adopted it in 1961 and designated it GRC-109.
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-1004A 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 become available in the meantime. The RS-1 went out of production in 1964 and was used well into the 1970s.
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

Receiver RR-2   R-1004A
The 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-3B receiver. It covers 3 to 24 MHz over 3 ranges:
  • 3 - 6 MHz
  • 6 - 12 MHz
  • 12 - 24 MHz

Transmitter RT-3   T-784
The transmitter was suitable for CW only and covers 3 to 22 MHz in 4 ranges. It contains just 2 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).   

Power Supply Units
Two different types of power supply are available for this set: a small one (RP-2) at the same size as the transmitter and receiver, and a large one (RP-1) that has a built-in power inverter.
Power Supply Unit RP-1   PP-2684
The RP-1 is the larger of the two power supply units. It can be used to power the RS-1 radio station from virtually any 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.
The RP-1 could also be used to recharge the 6V battery from the mains.

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

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.

The larger RP-1 power supply unit 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

Secure communication
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

Connecting the 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 [2].
Unit 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.
Description CIA Army designation
Complete radio set RS-1 AN/GRC-109
Transmitter RT-3 T784/GRC-109
Receiver RR-2 R1004A/GRC-109
Large PSU RP-1 PP-2684/GRC-109
Small PSU RP-2 PP-2685/GRC-109
Burst Encoder (optional) GRA-71 AN/GRA71
Hand-crank generator SSP-11 GN-58 (mod)
Maintenance kit (unmarked) CY-1321/GRC-109

  1. US Army, Coder-Burst Transmission Group AN/GRA-71
    TM 11-5835-224-12 (Operator and Organizational Maintenance Manual)

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

  3. Louis Meulstee, Wireless for the Warrior, volume 4
    ISBN 0952063-36-0, September 2004

  1. Supersedes TM 11-5835-224-45, 15 February 1967, and TM 11-5835-224-45P, 24 June 1966.

Further information

Any links shown in red are currently unavailable. If you like the information on this website, why not make a donation?
Crypto Museum. Last changed: Sunday, 16 August 2015 - 15:49 CET.
Click for homepage