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R-397 LK →
Spy radio transmitter

R-397-OK (Russian: P-397), codenamed OKOLSH (Russian: ОКОЛЫШ), was a transistorised short wave (SW) spy radio transmitter, used from 1975 onwards in counter-intelligence operations by the Russian military intelligence service GRU, and by the Russian special forces - the Spetsnaz. It is part of the IRTYSH (Russian: ИРТЫШ) radio system, which is highly resilient against jamming.

The transmitter measures 200 x 120 x 55 mm and weights 1200 grams. It covers the short wave radio band from 2.5 to 20 MHz, and has a range of approx. 1500 km, using just 1 Watt of power. It has a built-in digital memory (RAM) that can hold up to 20 groups of 5 characters.

To make it resistant against jamming, a relatively high bandwidth is used and a low data transfer rate of just 5 baud. 1 This means that to send a long 20-group message, the transmitter would be on the air for more than 3 minutes, making it vulnerable to radio direction finding (RDF).

Apparently, data integrity and resilience against jamming were more important than the risk of being detected and located. This is the opposite of what a burst encoder does in most other spy radio sets: reduce the risk of detection by sending the message at very high speed, at the cost of data integrity. The R-397-OK was commonly used in combination with the R-394-LK receiver.

  1. 5 baud = 6 groups/minute. Each group consists of 5 characters. Each character consists of 10 bits.

PLEASE HELP — At present we have no further information about the R-397-OK or about any other part of the IRTISH communication system. If you have additional information that you can share, please help us to expand and improve this page. We are looking in particular for circuit diagrams, manuals and photographs (and stories) about the use of the device in practice. We are also looking for a complete R-397-LK receiver.  Contact us
R-397-OK (Okolsh) transmitter - right angle view
 R-397-OK (Okolsh) transmitter - left angle view
With plug
1 / 5
R-397-OK (Okolsh) transmitter - right angle view
2 / 5
 R-397-OK (Okolsh) transmitter - left angle view
3 / 5
4 / 5
5 / 5
With plug

IRTYSH communication system
The R-397-OK was part of the IRTYSH radio system, which is shown in the diagram below. The transmitter was part of a radio link between the base station — the Centre – and the agent in the field — the Correspondent. The R-397-OK (OKOLSH) transmitter is shown in red at the top left.

Most components of the IRTYSH radio system have a model number that starts with R-397, followed by a two-letter suffix that determines the actual device. The first letter of the suffix indicates the name of the device (e.g. 'O' = OKOLSH), whilst the second letter tells us at which end of the radio link the equipment was used — field (agent) or base station (centre).

 More about IRTYSH

  • Device
    Digital spy radio transmitter
  • Purpose
    Low-power high-confidence agent communication
  • Model
    R-397-OK (Р-397-ОК)
  • Codename
  • Country
    Soviet Union (USSR)
  • Year
  • Users
    GRU, Spetsnaz
  • Principle
  • Frequency
    2.5 - 20 MHz in 10 kHz steps
  • Modulation
    MFSK 5ЦТ-20
  • Deviation
    4 kHz
  • Output
    1 to 1.8 W
  • Range
    1500 km
  • Memory
    20 groups 1
  • Data rate
    6 groups per minute 1
  • Bit rate
    5 baud
  • Power
    Battery, 12.8V, 0.8A (external)
  • Battery
  • Temperature
    -10 to +45°C
  • Dimensions
    202 x 122 x 62 mm
  • Weight
    1.3 kg (3 kg with accessories)
  1. 1 group consists of 5 characters.

  1. Сдам за Вас, Purpose and Features of the Irtysh Radio Line
    Retrieved February 2021. In Russian language. Via WayBack machine. 1

  2. Antonio Fucci, R-397 OK Transmitter USSR year 1975
    Retrieved February 2021.
  1. This website was no longer available in 2024. Data retrieved via WayBack machine.

Further information
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Crypto Museum. Created: Sunday 14 February 2021. Last changed: Thursday, 22 February 2024 - 07:05 CET.
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