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QRR-153 is a switch-receiver, used for remote control of a covert listening device (bug), made around 1979 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. The device is a 'chinese copy' of an existing switch-receiver that was discovered in the desk of a US Ambassador in the mid-1970s, and was commonly deployed alongside the matching SRT-153 transmitter (bug).
The QRR-153 is part of the SRS-153 surveillance system and reponds to ON/OFF command tones between 14 and 24 kHz, sent by a QRT-153 activation transmitter that operates on a factory-set spot frequency in the 68 - 78 MHz frequency band. The frequencies of the command tones are also factory-set and are accurately determined by two externally fitted miniature capacitors.

The receiver is operated from a single 1.35V mercury cell. To save power, it is only switched on for 23 ms every 1.5 seconds. It is estimated that it can operate this way for one full year.
QRR-153 switch-receiver with top cover (and white paste) removed

An electronic switch, that is part of the QRR-153, controls the power supply to the SRT-153 transmitter, so that it can be turned off when it is not needed, e.g. during the night. This way valuable battery power can be saved, whilst it also allows the surveillance team at the listening post to turn the transmitter off if the risk is too high, e.g. when a sweep team has been spotted.

The switch-receiver consists of three modules: a small superregenerative receiver and a two-tone decoder, each mounted in a separate metal case, plus an electronic switch that controls the power supply to the SRT-153 transmitter (i.e. the bug). The modules could be used separately, but were generally mounted together in a single metal case, with the switching unit mounted between the receiver and the decoder, as shown in the image on the right. The remaining space was then filled with a thick white silicone paste, after which the unit was hermetically soldered.
QRR-153 switch receiver QRR-153 switch-receiver (open and closed) QRR-153 switch-receiver with top cover (and white paste) removed The core parts of the QRR-153 switch-receiver Receiver Decoder Two-piece version of the QRR-153 switch-receiver Single-piece version of the QRR-153 switch-receiver

The QRR-153 was available in two case-variants:

The image below shows the interior of the QRR-153, after the top cover has been taken off, and the protective white silicone paste has been removed. The actual receiver is housed in the small square metal enclosure at the right. The bigger metal enclosure contains the tone decoder, which is 'programmed' by means of two external capacitors that are soldered to the wire terminals.

A single Siemens BC123 NPN transistor is mounted on a small PCB that is fitted in between the receiver and the decoder modules. It acts as the electronic switch that controls the power supply to the SRT-153 transmitter. At the far right are the terminals for microphone, antenna and power.

Complete setup
The diagram below shows a complete setup of the SRS-153 system. The QRR-153 switch-receiver is installed at the target area (TA) at the top right (shown in red). It is powered by a single Mallory mercury battery cell, and controls the power supply of the SRT-153 transmitter.

At the listening post (LP), which is generally located across the street from the target area, is the QRT-153 activation transmitter, which can send two carriers (one for the ON command and one for OFF) via a frequency in the 70 MHz band. It has presets for the control up to four QRR/SRT-153 sets simultaneously. Once activated, the signal from the SRT-153 transmitter can be picked up by the SRR-153 surveillance receiver at the bottom left, or by a modified SRR-90 receiver.
Block diagram
Below is the block diagram of the QRR-153 receiver. At the left is the superregenerative receiver which is pulse-operated by a battery saver that is part of the decoder module. The IF output of the receiver (video) is fed to two different tone filters inside the decoder module. They control the on/off state of a latch circuit, that in turn controls the external electronic transmitter switch.

The decoder is powered by a single 1.35V mercury battery, that indirectly powers the receiver. The power for the transmitter is provided by a string of 5 mercury cells that are connected in series, entering the external switch at the top right, and controlled by the state of the latch.

Alien bug
The QRR-153 is actually an accurate copy of the switch-receiver of an alien bug that was found by the CIA in the mid 1970s in the desk of one of its Ambassadors. It was hidden inside a wooden divider of one of the drawers of his desk. The image below shows the layout of the divider, with the receiver highlighted in red. It consists of three parts: a receiver, a decoder and a switch.

It is currently unknown why the CIA copied the design of an adversary, whilst they had access far better technology from a variety of sources. A possible explanation is that they wanted to put the blame on the adversary if the bug was discovered, or that it was used as a bait to satisfy an alien sweep team, and that other bugs, of a different nature, were also present at the target area.

 Read the full story

Although in principle, the QRR-153 switch-receiver can be used for remote controlling virtually any kind of bug, it was developed especially for use alongside the SRT-153.

The SRT-153 is housed in a similar metal enclosure, but is somewhat longer than the QRR-153. Furthermore it should be powered by a negative voltage, which explains the need for the extra switching transistor in the QRR-153.

 More information
SRT-153 and QRR-153

Remote control
In order to save power, the QRR-153 receiver is only switched on for 23 ms every 1.5 seconds. During the short time that it is active, it accepts ON and OFF commands sent by a transmitter in the 70 MHz band, in the form of a subcarrier.

The image on the right shows the QRT-153 activation transmitter, or actuator, that was developed especially for this purpose. It has provisions for controlling up to four QRR/SRT-153 sets simultaneously.

 More information
QRT-153 activation transmitter

The QRR-153 consists of three modules, two of which (the receiver and the decoder) are housed in an individual metal enclosure. The third module is no more than a single transistor, mounted on a small PCB. It acts as the electronic switch that controls the power supply to the SRT-153.
When encapsulated in a single enclosure, the electronic switch is mounted in the small space between the receiver and the decoder. The two other modules are solder-mounted to the sides of the enclosure. Like with the SRT-153 bug, the modules of the QRR-153 are filled with a sticky white silicone paste, which makes it very difficult to examine the interior. We are currently unable to show the interior of the receiver module.

Although the same is true for the tone decoder module, we have found the partly assembled bare one that is shown in the image on the right.
Decoder and (partly complete) interior

It is shown here aside a completely assembled encapsulated one. The tone decoder is built on a double sided PCB with components at both sides. The two large holes are for the Siemens ferrite inductors that are missing here. The inductors are used for the precision circuits that recognise the ON and OFF tones, sent by the QRT-153 activation transmitter at the listening post (LP}.
In order to provide some level of customisation, The exact frequencies of the command tones are determined in combination with two externally fitted capacitors. These capacitors are soldered directly to the wire terminals of the decoder module at the far end of the outer enclosure.

Once the individual modules were completely assembled, they were fitted onto a temporary test board, as shown in the image on the right. This allowed full testing and adjustment of the modules. In case of the three-piece variant, the QRR-153 was delivered to the CIA this way.
Two-piece version of the QRR-153 switch-receiver

In case of the single-piece variant, the individual modules were mounted inside a long metal enclosure and filled with white silicone paste. The case was then hermetically soldered and the complete unit was mounted on a slightly different test board. The single unit measures 93 x 18 x 6 mm. After acceptance and soak testing by CIA technicians, the modules were removed from the temporary boards and built inside the chosen concealment for actual target area deployment.

Although the construction of the QRR-153 is similar to that of the SRT-153 transmitter, there are significant differences in manufacturing and construction techniques, indicating that the original devices (from which these were copied) may have been manufactured by different suppliers.
Two-piece version of the QRR-153 switch-receiver Single-piece version of the QRR-153 switch-receiver QRR-153 switch-receiver (open and closed) Receiver (rear) and decoder (front) Switching transistor mounted between the receiver and the decode Switching transistor Decoder and (partly complete) interior Decoder, reverse side of PCB
Partly complete tone decoder (Siemens ferrite inductors missing) Decoder PCB - rear side Externally mounted capacitors Externally mounted capacitors Electronic switch (transistor) Contact terminals and receiver module Receiver Decoder

The diagram below specifies the wiring of the five contact terminals of the QRR-153 receiver. Note that pins 1 and 4 are internally connected to ground and that the device is powered by a positive voltage (i.e. minus connected to ground), whilst the SRT-153 transmitter is powered by a negative voltage and has the plus connected to ground. The receiver is powered by just 1.35V.
  1. Ground (-V)
  2. Power supply (+V)
  3. Switched output
  4. Ground (-V)
  5. Antenna
The diagram below shows how the QRT-153 is wired to the SRT-153 transmitter. The negative terminal of the battery array is directly connected to pin 3 of the transmitter, whilst the positive terminal is switched by the receiver. The receiver itself is powered by a separate 1.35V mercury battery. It has a built-in battery saver that switches it on for just 23 ms every 1.5 seconds.

Note that transmitter and receiver each have their own antenna, which more or less resembles a dipole. One half of the dipole is formed by the antenna wires, whilst the ground wiring acts as the other half. In the orignal desk drawer divider (in which the bug was first found), the ground wires are clearly visible just above the battery array. Antennas of this kind are by no means ideal.
  1. XSRT/XQRR-53 Operating Notes
    NRP, October 1977. CM302627/A.

  2. Proposal for Prototype SRS/QRS-53
    NRP, November 1977. CM302627/B.

  3. Environmental Test Report on XQRR-53 Receiver
    NRP, August 1979. CM302627/G.

  4. Operation and Test Manual for SRT-153 & QRR-153
    NRP, April 1980. CM302627/H.

  5. Operation and Test Manual for SRT-153 & QRR-153
    NRP, May 1980. CM302627/I.

  6. Operation and Test Manual for SRT-153 & QRR-153 (draft)
    NRP, September 1980. CM302627/J.

  7. Operation and Test Manual for SRT-153 & QRR-153
    NRP, September 1981. CM302627/N.

  1. NRP/CIA, Collection of documents related to SRS-153
    Crypto Museum Archive, CM302627 (see above).

Further information

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Crypto Museum. Created: Thursday 18 May 2017. Last changed: Thursday, 18 May 2017 - 14:45 CET.
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