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Homing radio receiver - this page is a stub

HRR-26 was a homing radio receiver, or radio direction finder for the 40-45 MHz radio band, manufacturered around 1975 by Ocean Applied Research Corporation (OAR) for the US Central Intelligence Agency (CIA). The receiver was part of the HRS-26 homing system and was intended for tracking vehicles in an urban environment. It was later improved significantly by the NRP.

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.

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.

Horizontal polarization
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

  1. XHRS-26 Direction finder
    6 September 1975.

  2. Operating Manual for Direction Finding Antenna (prototype)
    NRP/CIA. July 1977.
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Crypto Museum. Created: Sunday 26 March 2017. Last changed: Friday, 01 September 2017 - 05:36 CET.
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