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← URS-3
← Easy Chair
Universal radio receiver

URR-3 was a universal radio receiver, developed around 1975 by the Dutch Radar Laboratory (NRP) for the US Central Intelligence Agency (CIA), as part of the URS-3 path loss survey system, under the Easy Chair research contract. The receiver was used for analysing the link budget 1 of a communications system, consisting of a covert listening device (bug), a surveillance receiver and two antennas. The results of the survey could be recorded on an (optional) data pen-recorder.

The receiver was usually connected to an SRN-55 antenna that was also suppied by the NRP. For site surveys, it was used in combination with an URT-3 transmitter, which operated at a fixed spot frequency in the 1380 MHz UHF band.

The results from the survey can be read directly from the meter at the top right of the front panel, but can also be printed on paper, using the supplied pen recorder, or recorded onto magnetic (audio) tape, on an (optional) UHER tape recorder, allowing the data to be processed later in the environment of the head office.
URR-3 receiver

Although it was possible to play back the recorded data on the URR-3 receiver itself, this was usually done on the (optional) URR-3 Replay Unit. The latter was a copy of the URR-3 receiver from which the RF front-end and the IF-section were omitted. Replay units were usually installed at the head office, allowing the survey data to be processed more accurately. Existing Replay Units could be converted to a full URR-3 receiver, by installing a seperately available upgrade kit.

As we do not have a complete URR-3 receiver in our collection, we are showing the replay unit instead. The front panel is identical, bu the position of the RF-input socket (below the meter) is covered by a metal panel that is labelled REPLAY UNIT. It is our intention to eventually convert this unit into a fully operational URR-3 receiver. Note that the URR-3 is a wideband receiver (25 MHz), whilst the very similar URR-4 receiver is only suitable for narrowband signals (30 kHz).

URR-3 receiver Front panel
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URR-3 receiver
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Front panel

The diagram below shows the control panel of the URR-3 Replay Unit, which is identical to that of the URR-3 Receiver, with the exception of the blank panel at the bottom right, marked REPLAY UNIT. On the actual receiver this panel is replaced by the RF input socket for the antenna.

The device has neither a built-in mains power supply unit (PSU), nor a connection for an external one. Instead, it is powered by a series of common 9V block batteries, installed in a removable battery pack at the rear, identical to the one that is used in the contemporary SRR-90 receiver. Several years after the introduction of the URR-3, an (optional) plug-in power supply unit (PSU) was released, that could be installed in the bay that was normally taken by the battery pack.

Receive antenna   SRN-55
A suitable 1600 MHz directional antenna should be used with the URR-3 receiver, such as the SRN-55 shown in the image on the right.

Initially, this antenna was not part of the URS-3 survey set, but from 1977 onwards, it was supplied as standard with every URR-3 receiver.

 More information
SRN-55 directional antenna

Data recorder   RE-501
When performing a site survey, the results of the path loss measurements can be printed onto paper, using the Goertz RE-501 MINOGOR pen recorder shown in the image on the right.

The device is battery powered and prints the data, relative to time, onto a 20 cm wide thermal paper strip for later processing.
Goertz Minigor RE-501 data recorder

Tape recorder   UHER
In addition to printing the measurement data onto paper, it was also possible to record it onto a magnetic (audio) tape, using the UHER recorder shown in the image on the right.

UHER tape recorders were very popular during the 1960s and 1970s, as they were among the first affordable portable tape recorders with professional performance.

 More information

UHER 4000 Report-S

The URR-3 is housed in a strong aluminium case in bright green colours. It consists of a frame to which all parts are mounted, enclosed by a green case shell. After removing a single screw from the rear side, the case shell can be removed, exposing the interior, as shown in the image below.

Looking at the receiver from the rear, there are three plug-in cards that can be removed from the side. These cards hold the Filter board, the VFV converter board and the LOG & DC board.

The space between the plug-in cards and the front panel is normally taken by the RF front-end. It is empty here, as the device shown here is the Replay Unit. At the right are two bays. The large one is for the battery pack, whilst the small one at the bottom takes the 60 MHz IF-unit.

More information will be added as and when it becomes available.

URR-3 with case shell removed Interior URR-3 chassis, seen from the top Filter board detail Front panel wiring Three plug-in cards Battery pack IF module
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URR-3 with case shell removed
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URR-3 chassis, seen from the top
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Filter board detail
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Front panel wiring
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Three plug-in cards
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Battery pack
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IF module

  1. Mic out
  2. Ground
  3. Mic in
  4. Tone out
  5. Tone in
  1. Mic in
  2. Ground
  3. Mic out
  4. Mic in (shorted to 1)
  5. Mic out
  1. MOR relay contact (with 4)
  2. Ground
  3. COR relay contact (with 5)
  4. MOR relay contact (with 1)
  5. COR relay contact (with 3)
Technical specifications
  • Frequency
    1000 - 1600 MHz
  • IF frequency
    60 MHz
  • Bandwidth
    25 MHz
  • Subcarrier
    20 kHz
  • Path loss indication
    quasi logarithmic
  • SC bandwidth
    10 kHz
  • Indicating ranges
    30-100 and 60-130 dB
  • Demodulation
    Compatible with URT-3
  • Audio out
    1 mW into 600 Ω
  • Temperature
    0°C to +60°C
  • Power supply
    Internal, 4 x 9V block battery
  1. Engineering Report for XURS-3
    NRP, August 1974. CM302516/A.

  2. Collection of notes, correspondence and circuit diagrams related to URS-3
    NRP, December 1975 - November 1976. CM302516/B.

  3. Manual for URS-3
    NRP, November 1976. CM302516/C.

  4. Manual for URS-3
    NRP, December 1976. CM302516/D.

  5. Proposal for Production of URS-3 Systems
    NRP, March 1977. CM302516/E.
  1. NRP/CIA, Collection of documents related to URS-3
    Crypto Museum Archive, CM302516 (see above).
Further information
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Crypto Museum. Created: Thursday 10 August 2017. Last changed: Sunday, 13 August 2017 - 16:29 CET.
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