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The HRR-26 was based on an existing OAR direction finder, such as the
ADF-210, ADF-320
and the ADF-940
shown in the image on the right. The receiver consists of a fixed cathode
ray tube (CRT) in a metal blue enclosure, and a configurable receiver unit
that was mounted in a large cut-out at the right half of the front panel.
The HRR-26 uses the Adcock principle,
which is suitable for direction
finding at sea, but less so for urban areas where reflections on
buildings seriously impair the effectiveness. It provides the best results with vertically polarized signals.
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The CIA wanted to use the HRR-26 and other direction finding systems like
the HRR-18, for
unobtrusively following and tracking a vehicle whilst driving around in a city.
Field tests by the CIA in 1975 and 1976 showed that it was difficult to
follow the (weak) signal of a homing transmitter (beacon) that had been
covertly installed in a suspect's car. This was mainly due to the low
transmitting power of the beacon, but also by the lack of sensitivity of
the HRR-26.
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To improve the performance of the HRS-26 system, the CIA turned to the
Dutch Radar Laboratory (NRP)
to develop a new antenna system that would be
suitable for the existing direction finding systems operating in the 40 to
45 MHz band. In July 1977, the NRP delivered a usable prototype,
along with full documentation [B].
This included the use of SRA-3S pre-amplifiers.
➤ Detailed description of the ADF-940
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© Crypto Museum. Created: Sunday 26 March 2017. Last changed: Sunday, 27 August 2023 - 07:37 CET.
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