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Osobnjak 8
Wideband field strength indicator - wanted item

Osobnjak 8 was a field strength indicator for RF signals between 100 MHz and 12 GHz, developed in the USSR in the 1980s, as a technical countermeasure against the resonant cavity microphone, a passive covert listening device (bug), that was activated by a stong RF signal from the outside, similar to The Great Seal Bug, or The Thing. The device is also known by its designator 1RTA7.

In 1945, the Russians had been the first to apply a resonant cavity microphone, when they built one inside a wooden carving of the Great Seal of the United States, that was presented as a gift to US Ambassador Averell Harriman in Moscow.

The device remained undetected for seven years, during which time it had provided the Russians with the best possible intelligence. The main advantage of the device was that it was difficult to detect, as it contained no electronic parts and was not connected to any wires. Furthermore, it did not have its own power source. Instead it was activated by a strong RF beam from outside.
Osobnjak 8 with open lid. Photograph kindly supplied by Detlev Vreisleben [1].

After the Americans had discovered the device in September 1952, the technology became known to the Western world and equivalent devices were developed by several agencies in the US, the UK and The Netherlands, along with suitable countermeasures receivers. The devices were extremely difficult to detect with existing countermeasures techniques, as they had to be activated by an RF signal of a precise frequency first. Having invented the device in the first place, and expecting the Western agencies to develop similar devices, the Soviets developed their own countermeasures.

OSOBNJAK 8 is an example of such a Russian countermeasure. The device is housed inside a common briefcase and is powered by internal rechargeable batteries that are suitable for approx. 4 hours of uninterrupted operation.

The device is actually a field strength indicator that can detect nearby RF signals between 100 MHz and 12 GHz, divided over 8 frequency ranges, each of which has its own antenna. The antennas are hidden inside the case's lid and each one has an opening angle of about 90°.

The image on the right shows the antennas after the metal cover of the top lid of the briefcase is taken off. Note the 8 feed lines at the bottom.
Inside the top list of the Osobnjak 8 briefcase. Photograph kindly supplied by Detlev Vreisleben [1].

Also note that some of the antennas are made of PCB material. The device is small enough to be hand-carried into a room unobtrusively, and can be operated without any particular skills. It is likely that the Soviets had it installed in every room where important meetings were about to take place. Any strong RF microwave signal, beamed at the office, would be detected immediately.

Today (2015) a field strength detector like this would hardly be of use, as we are now surrounded by strong microwave signals from GSM base stations and other digital communications systems. Furthermore, later generations of passive bugs had a built-in battery that was charged outside operational hours, so that no strong external RF signal was needed during the actual operation.

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Resonant cavity microphones
A resonant cavity microphone is a specific type of bug that does not have its own power source. Instead it is powered by a strong microwave signal that is aimed at it from some distance, varying from 30 to 300 metres. The devices are also known as Retransmission Bugs or Passive Elements. Although the Russians were the first to make use of them, they were by no means the only ones. The devices were copied and improved by Western agencies. Here are some examples:

Technical specifications
  • Ranges
    8 (see below)
  • Antenna angle
  • Batteries
    2 circuits with 4 x R-20 battery each
  • Operation
    Approx. 4 hours
  • Indicators
  1. 100-205 MHz
  2. 190-500 MHz
  3. 460-850 MHz
  4. 840-1520 MHz
  5. 1470-2750 MHz
  6. 2620-5000 MHz
  7. 4900-8000 MHz
  8. 7800-12000 MHz
  • Range I-IV
    95 dB/µV (adjustable)
  • Range V-VIII
    102 dB/µV (adjustable)
  1. Bedienungsanleitung für das Gerät 'OSOBJNAK 8'
    Date unknown. Two-page instructions (German) kindly supplied by [1].
  1. Detlev Vreisleben, Images and documentation of Osobnjak 8 device
    Personal correspondence January 2016.
Further information
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Crypto Museum. Created: Tuesday 12 January 2016. Last changed: Saturday, 16 July 2022 - 08:32 CET.
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