Spy radio
Burst encoders
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R-350   Orel - Орел
Russian spy radio set (Eagle)

The R-350 was a Russian spy radio set that was developed in the former USSR around 1955 as the successor to the post-war Electron (or 'Elektron') radio set. The Electron had an output power of 50W and was suitable for ranges up to 3000 km. It was one of the first true spy radios that used a burst encoder in order to minimize the risk of interception and direction finding by the enemy. The R-350 used the same burst encoder. The R-350 was developed by the KGB Research Institute, probably in Kuchino (near Moscow) [1]. It was succeeded in 1957 by the R-350M.
Compared to the Electron, the R-350 was more robust and was therefore much more suitable for use by the Russian Armed Forces. It was used by Special Forces, the GRU, for reconnaissance at the battle front and behind enemy lines. It was available with Russian text on its front panel, but also in English, especially for its foreign users.

The image on the right shows a typical R-350 radio set with English front panel. It can be recognized by the rectangular filter blocks used for the transmitter. Only one filter can be installed in the transmitter at any time. The remaining 7 filters are stored inside the case lid.

The R-350 is extremely service-friendly. All valves (tubes) - except for the TX power valve - are accessible directly from the front panel and can be extracted by pulling the black knob on top. Spare valves are stored inside the top lid. A spare TX power valve is also supplied, but that requires the TX module to be removed first.

The R-350 was designed as a self-contained mid-range transceiver with an HF output power of approx. 6W. The base of the unit consists of a transmitter (right), a receiver (left) and a power supply (behind the other two). At present, any knowledge about the power supply is missing.
R-350 with its lid open

The R-350 was the first Russian spy radio to be put into mass production and for a long time it was the most popular radio set, until it was replaced around 1957 by the improved R-350M. The R-350M became even more popular than the R-350, as it was also supplied to other countries of the Warsaw Pact, such as the DDR (East-Germany). The original R-350 (shown here) is extremely rare. In the mid-1960s, the R-350 and the R-350M were replaced by the R-354 (Schmel).
R-350 case R-350 case R-350 radio station Frequency table (tuning charts) Tuning charts Note pad Removing the TX filter

  • R-350
    This is the basic model that can be recognised by its rectangular filter units. One of these filters is inserted into the transmitter. The remaining filter units are stored in the top of the lid. This version is described on this page. Radio sets of this type are extremely rare.

  • R-350M
    This is a slightly modified version of the R-350. It was introduced around 1959 and can be recognised by its cylindrical filter units. Radio sets of this type are also very rare, but not are rare as the earlier R-350 model as they were also deployed in the DDR (East-Germany). For more information about the R-350M click here.

Audio samples
Below are some audio samples of the R-350M, recorded by karsten Hansky in Germany [4] in June 2014. The radio was connected to a dummy load and an ELAD FDM-S1 was used to receive and record the signal. Further sound processing was done with Audacity.
The R-350 is wired in such a way, that the transmitter and receiver are easily removable. Once the bolts at the edges of the front panel are removed, the module can be lifted out. It is connected to the rest of the radio by means of a connector that mates with a socket inside the case. The radio consists of the following functional blocks:
  1. Transmitter (TX)
  2. Receiver (RX)
  3. Power Supply (PSU)
  4. Burst transmitter

The first two blocks are truly modular. The receiver (RX) is located at the front left, while the transmitter (TX) is mounted on the right. The transmitter can be removed by releasing the 4 bolts at the corners of the front panel. The transmitter is connected to a socket that is fixed to the receiver. Once the transmitter is removed, the receiver can be removed in the same manner.
The main R-350 unit The rectangular filter in the transmitter The filter extracted from the transmitter The frequency tables Some pages of the frequency tables The power connector

The image on the right shows the transmitter (block 1) once it is removed from the case. The interior is constructed in the usual manner for the era. The two 'standard' valves are both recessed by means of an aluminium 'beaker' with a socket at the bottom. They can be accessed from the front panel.

The power amplifier valve can only be accessed from the rear. If it is broken, the transmitter needs to be removed from the case. A spare power valve is stored inside the top lid of the case.

Transmitter Transmitter interior Transmitter interior Transmitter power amplifier valve (tube) Tuning coil

The receiver is a two-stage super-heterodine design, built with 2ZH27L valves (2Ж27Л). The LF output is about 4mW, which is suitable to drive a standard Russian 150 ohn headset, which is connected at the top left.

The image on the right shows a typical receiver once it is removed from the case. The connector at the right is the receptacle for the transmitter.

Receiver Receiver interior Receiver interior

Power Supply
There are still many questions about this radio. From all R-350 radios we've seen so far, the power supply has been missing. This means that we do not know whether this radio had a built-in power supply or an external one. We are also looking for the original manual of the R-350. If you have any information about this radio, please contact us.
The image on the right shows a set of 6 wire terminals that are used to feed the various voltages to the radio. It is possible that an external power supply was connected here.

It is far more likely though, that a power converter (probably with a vibrator) was built inside the emply space below the power terminals. So far, no evidence has been found however, to substantiate this.
Power terminals

Power terminals Power connector

Most of the accessories are storied inside the top lid. With a standard unit, the following extras are usually supplied:
  • Additional filter units (7)
  • Spare valves
  • Spare transmitter valve
  • Work light
  • Message puncher (burst encoder)
  • Morse key with burst transmitter
  • Wire antenna
  • 35 mm photo film (inside container)
Message puncher
Each message is first translated into a series of numbers. This is usually done with some kind of cipher system, such as a simple matrix or the unbreakable One Time Pad (OTP). The numerical message is then stored on a a standard 35 mm photo film by punching a series of holes in it, using the device shown here.

 More information
Click for more information about the burst encoder

Burst transmitter
The R-350 is supplied with an external morse key with integrated burst transmitter. Photo film with the punched numerical message can be fed into a narrow slot at the front of the morse key.

A small crank is then used to feed the film through the transmitter at a constant speed.

 More information
Click for more information about the burst encoder

  1. Radioscanner website, R-350 'Eagle'
    Brief description of R-350 (Russian). 2006. Retrieved March 2012.

  2. Ivan Petrov, Radio Communications Facilities in Service with Military Intelligence
    Major General (Retired), Military Parade JSC website, 1998.

  3. R-350 Circuit Diagram
    Unknown source. Date unknown.

  4. Karsten Hansky, Sound samples of R-350M transmitted signals
    Germany, June 2014.

Further information

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Crypto Museum. Created: Tuesday 03 November 2009. Last changed: Sunday, 02 October 2016 - 08:33 CET.
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