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Covert listening device with RP audio masking - under construction

SRT-56-F is a covert listening device (bug), developed in 1968 by the Dutch Radar laboratory (NRP) for the US Central Intelligence Agency (CIA), as part of a long-term research contract under the codename Easy Chair (EC). The device features the Rejected Pulse (RP) audio masking scheme.

The SRT-56-F is based on the design of the SRT-56 and is in fact the combination of the SWE-56 video encoder and the SRK-35 RF-unit, albeit in a single rectangular enclosure. The device operated in the 315 - 385 MHz band. It was powered by a DC source between +5 and +8V, and consumed 4.5mA, wilst delivering a peak-output-power of 75mW.

The device is compatible with, and can be decoded by, the SRR-52-M, SRR-56, SRR-90 and SRR-91 receivers. It was powered by the UWP-56 power module, or by a 4-cell mercury battery.
SRT-56-F (later version)

The device was commonly used in combination with a Sleevex Band 2 target antenna, whilst an SRN-9H or SRN-9 antenna was used at the listening post. The first prototypes of the SRT-56-F were ready for evaluation in April 1968. The device was first used in the field in February 1970 and was in production until at least 1973. The SRT-56-F is part of the CIA's SRS-56 surveillance system. For further information please refer to our page about the SRT-56.

    This page currently acts as a placeholder for future information about this item, and will be updated as and when new information becomes available. If you have additional information, please contact us.
Two variants of the SRT-56-F SRT-56-F with Sleevex antenna SRT-56-F with Sleevex antenna SRT-56-F (later version) SRT-56-F SRT-56-F compared to the size of a hand Wiring of the later version Connector
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Two variants of the SRT-56-F
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SRT-56-F with Sleevex antenna
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SRT-56-F with Sleevex antenna
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SRT-56-F (later version)
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SRT-56-F compared to the size of a hand
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Wiring of the later version
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Technical specifications
  • Frequency
    315 - 385 MHz (pre-determined spot frequency)
  • Audio masking
    Rejected Pulse (RP), also known as Type 56 modulation
  • Power
    +45 to +8 V
  • Current
    4.5 mA
  • Output
    75 mW (peak output power)
  • Supply
    UWP-52, UWP-56 or 4-cell battery
  • Antenna
    Sleevex Band 2
Further information
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Crypto Museum. Created: Thursday 09 March 2017. Last changed: Tuesday, 13 June 2017 - 06:23 CET.
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