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Easy Chair
UVK-21 →
VSWR tester for covert antennas

UVK-20 was a Voltage Standing Wave Ratio (VSWR) meter for RF signals in the 120 to 500 MHz frequency range, developed in the late 1970s by the Dutch Radar Laboratory (NRP) for the US Central Intelligence Agency (CIA), as part of a long-term development contract named Easy Chair.

Unlike most VSWR meters, which are connected in-line between an RF source (e.g. transmitter) and a load (e.g. antenna), the UVK-20 uses an internal source. This makes the device ideal for testing the performance of an antenna system.

It allowed the CIA to test any type of antenna in a variety of situations, so that the performance of a covert listening device (bug) could be tested (and validated) under realistic circumstances. The image on the right shows a prototype of the device. 1 It has two frequency ranges: LO (blue) 120 - 300 MHz and HI (red) 300 - 500 MHz.
UVK-20 VSWR meter (prototype)

UVK-20 was developed by the NRP at the time when the company was no longer developing new covert listening devices for the CIA, but was still doing research under the Easy Chair contract. This resulted in a series of (bug) receivers and measurement devices, such as the UVK-20. In parallel with the UVK-20, the NRP also developed the UVK-21, which was an in-line VSWR meter.

Development of the UVK-20 started as early as 1974, with a series of tests, experiments and prototypes for various frequency ranges, including 40-50 MHz and 240-420 MHz. The latter includes the popular UHF frequencies in the 380 MHz range, as allocated by the CIA for bugs. Final production of the device took place between 1980 and 1982, but the quantity is unknown.

  1. The device shown here is labelled XUVK-20. The 'X'-prefix was used by the CIA to identify prototypes.

UVK-20 in grey plastic storage box UVK-20 in storage box UVK-20 VSWR meter (prototype) Frontal view Battery compartment (2 x 9V)
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UVK-20 in grey plastic storage box
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UVK-20 in storage box
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UVK-20 VSWR meter (prototype)
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Frontal view
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Battery compartment (2 x 9V)

Known models
Similar equipment
Inline VSWR meter Transmitter tester Path loss survey system for 316 MHz Path loss survey system (wideband) for 1380 MHz Path loss survey system (narrowband) for 170 and 316 MHz
  1. UVK-20 VWSW Tester, Operation and Test Manual
    CM-302542/D. NRP, May 1979.

  2. XUVK-20 VWSW Tester, Environmental test report
    CM-302542/E. NRP, August 1979.

  3. UVK-20 VWSW Tester, Operation and Test Manual
    CM-302542/J. NRP, June 1982 (A5 format).
Further information
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Crypto Museum. Created: Saturday 12 October 2019. Last changed: Sunday, 13 October 2019 - 14:26 CET.
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