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UHF intercept receiver

Přístroj 1 was a UHF intercept receiver, developed around 1968 in Czechoslovakia by Správa 6 2 for use by the secret intelligence agency (StB) and by Správa 1 (espionage) in counter-counter-espionage operations. The device was designed to receive a fixed frequency in the 465 MHz band and was used in Paris (France) for monitoring communication of the French counter-espionage.

The image on the right shows a typical Pristroj receiver that was normally connected to a tape recorder. It has only two controls: Volume and RF Gain, plus two indicators: Power and Record.

During the cold war, Czechoslovakia had a large number of spies and secret agents on active duty in France. Although most of them worked under the diplomatic cover of the embassey, nearly all of them were on the payroll of the StB, the ZS GŠ or Správa 1. As a result, many of them were followed by the French counter-espionage as soon as they started walking the streets of Paris.
Pristroj UHF intercept receiver (465 MHz)

For covert communication between agents of the counter-espionage agency, the French used portable radios that operated on 465 MHz. No encryption was used on these voice channels, as the French believed that, due to the very high frequency that was used, the signals would not be intercepted. Communications receivers for these frequencies were not mainstream at the time.

Přístroj was developed in-house by Správa 6, and several units were used simultaneously to monitor all radio channels of the French counter-espionage. Each device was marked with one of the letters of the alphabet, probably indicating the frequency. The device was introduced in 1968 and was an instant hit. It produced great intelligence on a daily basis for many years.

  1. Přístroj is the Czech word for Device.
  2. Správa 6 refers to Government Department 6: Communication Technology.

Pristroj UHF intercept receiver (465 MHz) Front panel Rear panel Sockets and fuse (rear panel) A stack of Pristroj receivers
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Pristroj UHF intercept receiver (465 MHz)
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Front panel
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Rear panel
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Sockets and fuse (rear panel)
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A stack of Pristroj receivers

Despite its simple and almost boring look, Přístroj was an extremely effective tool. Rather than using a Variable Frequency Oscillator (VFO), each device was configured for a single frequency of the French counter-espionage by means of a fixed crystal. As a result, multiple devices had to be used, usually powered by a common 12V DC power source. The 465 MHz input of all devices came from a single antenna with a distribution amplifier. The RF Gain can be adjusted at will.

The unit is switch on by turning the Volume knob away from the OFF-position. The green LED will come on. Whenever a sigal is intercepted, the red LED lights up and the message will be heard through the speaker or the connected headphones. At the same time a relay is activated, allowing an (optional) recorder to be switched on as well (REC). This also allows unattended recording.

The receiver is housed in a modern modular aluminium enclosure that measures only 27 x 18 x 7 cm. The top panel can be taken off by removing four bolts at the corvers. Likewise, the bottom panel can be taken off by removing the four feet on which the unit stands. This exposes a frame.

The electronics inside the frame can be divided into three modules, each of which seems to be developed by a different design team. At the front left is a grey hammerite metal box that contains a downconverter. It converts the 465 MHz signal into an easier to handle 74 MHz one.

At the front right is the control board that holds three electric relays with the driving transistors, an AF pre-amplifier and the AF audio amplifier that delivers the speaker signal. The actual 74 MHz receiver is mounted on a subframe close to the rear, and has a highly modular design.
Interior (top side)

The modules are mounted onto a single PCB that is marked with the project number TI-574B. It incorporates a complete crystal-operated double-superheterodyne receiver, with selective tone call, squelch and switched output. Similar modules were used in the TI-574A transmitter that was part of the Štěnice radio bug. The downconverter is known as project number TI-640A.

Interior (top side) Top view Bottom view Control board Control board (seen from front) Frequency converter Modular receiver Receiver (bottom view)
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Interior (top side)
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Top view
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Bottom view
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Control board
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Control board (seen from front)
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Frequency converter
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Modular receiver
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Receiver (bottom view)

Block diagram
A complete Přístroj station consisted of five modules: the main receiver (described here), a tape recorder (possibly an UHER Report 4000), a central clock facility, a time-code inserter and a 12V central power supply unit (PSU). Only the actual 465 MHz intercept receiver (RX) is described here.

The receiver is build from various more or less standard components plus a purpose built control board with several relays. The three main blocks are shown in the diagram below. At the top left is the transverter that converts the intercepted 465 MHz signal down to 74 MHz. This block is known as project TI-640A. The 74 Mhz signal from the converter is fed into a crystal-operated double superheterodyne receiver that is constructed from a range of standard modules.

The receiver includes an automatic squelch, a single-time selective call unit, an emitter follower (to drive a relay) and an audio amplifier that delivers the LF output at speaker level. The standard modules from which the receiver is constructed, allow a high degree of customisation and flexibility, whilst reducing development time and cost. Similar modules were used in various other devices, such as remote control units, electronic dead letter boxes and radio bugs like Štěnice.

The device has three DIN sockets at its rear panel: one 3-pin 180° female socket and two 6-pin 240° female sockets. The 3-pin socket carries the audio at line level plus a relay contact. The two 6-pin socket are connected in parallel (all 6 pins 1:1). These sockets are used for 12V DC power input, line-level audio output and a relay contact for automatically starting a tape recorder.

Audio line out
  1. Audio
  2. Ground
  3. Record (switched contact to ground)
Power and recording
  1. Audio (line out)
  2. Ground
  3. Record (switched contact to ground)
  4. 12V DC
Project numbers
  • TI-640A
    465 MHz to 74 MHz downconverter
  • TI-574B
    74 MHz double superheterodyne FM receiver
  1. Přístroj circuit diagram (incomplete)
    TI-640A (converter), TI-574B (74 MHz receiver). Date unknown.
  1. Anonymous, Přístroj 465 MHz intercept receiver - THANKS!
    Receiver and documentation kindly donated by anonymous former user. July 2015.
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