Spy radio
Burst encoders
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Clandestine spy radio station

SIRIUS, or SIRIUS I, was a modular spy radio set, developed and built in Czechoslovakia between 1958 and 1962 by Správa 6 1 for the secret state police (StB) and Sprava 1 (espionage). It was the successor to the PLUTO spy radio set and was mainly deployed for clandestine operations in West European countries. The set is also known as AB, the transmitter's model number suffix.
Unlike previous spy radio stations, which used classical telegraphy by means of a manually operated morse key, SIRIUS was the first one to use a high-speed burst encoder that allowed 200 groups 2 to be transmitted in 15 seconds.

The image on the right shows a more or less complete SIRIUS setup which consists of a PLUTO receiver, a SIRIUS AB transmitter and a SIRIUS D tape-based recorder (burst encoder). Further­more, several accessories are shown, which were normally stored inside a SIRIUS P accessory box. Unfortunately the accessory box is missing here.
Complete SIRIUS spy radio station

Development of the SIRIUS spy radio station started in 1958, a few years after the lauch of the PLUTO station, and it should be no surprise that it was inspired on the American RS-6 spy radio set. was introduced. The first set was delivered in 1962. It is currently unknown how many SIRIUS stations were manufactured, but it is possible that the one shown here is the only surviving one. SIRIUS was succeeded in 1966 by SIRIUS III and possibly before this by the SIRIUS II radio set.
  1. Správa 6 refers to Government Department 6: Communication Technology.
  2. In this context, a group consists of 5 numerical digits (0-9).

Complete SIRIUS spy radio station PLUTO receiver, SIRIUS transmitter and (prototype) burst encoder PLUTO receiver connected to the SIRIUS transmitter

Transmitter   TI-466 AB
The transmitter is known as TI-466AB or just AB and is the largest module of the SIRIUS radio station. Contrary to the other modules, which are plainted grey hammerite, the AB is black.

The transmitter is free-running and has a built-in crystal calibrator. It also has a built-in mains PSU that is used to power the receiver as well. The TI-466AB delivers an output power of 80W.

 More information
TI-466AB transmitter

Receiver   TI-462 A
SIRIUS did not come with its own receiver. Instead the small valve-based TI-462 receiver of its predecessor PLUTO was supplied with the set. It is powered directly from the transmitter, which has an appropriate DIN socket at the left rear.

As the SIRIUS spy set came with a high-speed morse burst encoder, the built-in automatic morse keyer of the TI-462 was no longer needed and is therefore omitted from the TI-462 A.

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PLUTO receiver (TI-462A)

Burst encoder   TI-485
With the SIRIUS spy radio set, high-speed morse burst transmissions were introduced to the Czechoslovakian spy scene by means of the TI-485 recorder shown here. It allows pre-recorded numbers (0-9) to be played back at high speed.

Two versions of the TI-485 are known to have existed, the first one being called DÁVAČ (keyer) and a later one known as MĚSIC (moon), with the one shown here being the later one.

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MESIC burst encoder using with SIRIUS III spy radio set

Accessory box   TI-466 P - wanted
A small metal box was supplied with the set. It contained all accessories, such as earphones, crystal(s), wire antennas, voltage checker, etc.

As the accessory box has the same dimensions as the PLUTO receiver, it is probably identical to the one that was supplied with that set.
Pluto accessory box. Photograph copyright Detlev Vreisleben [2].

Transport case
For transport and storage, the complete SIRIUS set was usually stored insed the wooden box shown here. The transmitter is stored in the lower half of the case, whilst the receiver, the accessory box and the burst encoder are fitted inside the top half of the case.

Together, the size of the three parts shown at the front, matches the size of the transmitter. Click for a close-up.
Complete SIRIUS spy radio set in storage box

Mains voltage checker Set of crystals Earphones Cable for burst encoder Mains power cable Wind-up antenna

Mains checker
The order to check whether the mains voltage is present and to determine its average voltage, a small mains checker in the shape of a universal mains plug was supplied. One of its sides is transparent allowing the operator to watch the internal neon lamp (closest to the contact pins).   
Mains voltage tester

Set of crystals
As the TI-466 AB transmitter is free-running (i.e. it can be adjusted to any frequency in the 4-16 MHz range), it does not require crystals for its operation. In order to calibrate the frequency scale however, an internal calibrator was used.

The internal calibrator needs an external crystal with a frequency around 120 kHz. Examples of such crystals are shown on the right.

The SIRIUS spy radio set was supplied with two earpieces: one for the PLUTO receiver (shown here) and a similar one for the calibration circuit of the transmitter. The latter had a slightly different connector.

Earphones of this type were rather common in those days, as they were also used with the hearing aids of the era.

Cable for burst encoder
A short cable was supplied for connecting the burst encoder to the transmitter. The burst encoder was usually placed in front of the transmitter, which is why this cable was so short.   
Cable for burst encoder

Mains power cable
This power cable was used to connect the TI-466 AB transmitter to the mains AC network. By using a slimline plug with just two pins, it will fit most of the common wall sockets in Europe.

The power supply unit (PSU) of the TI-466 AB could be adjusted for a variety of mains voltages, making it possible to operate the radio virtually anywhere in the world.
Mains cable

Wind-up antenna
The SIRIUS radio station was supplied with the 9.6 metre wind-up antenna shown here. It is very similar to the ones used with West European spy radio sets, such as the German SP-15 and the British Mk-123.   
Wind-up antenna

Morse key Morse key Operating the morse key Mains voltage tester Crystals Earphones

The SIRIUS spy radio station was used by secret agents and spies for sending (coded) messages to their control at the Czechoslovakian headquarters (HQ). At the receiving end (i.e. at HQ), the high-speed morse burst transmissions were recorded onto tape and then played back at normal speed, so that they could be written out again. At HQ, the following setup was used for reception:

UPA   Pulse shaper
UPA was a so-called pulse shaper that was one of the most important parts of the SIRIUS reception station in Czechoslovakia. It re-shaped the rather noisy CW tones from the HF receiver, so that they could be written to a paper tape by means of a HELL undulator (morse writer).   
UPA pulse-shaper

Tape recorder   Javornik TI-447
JAVORNIK was a standard tape recorder/player, made by the Czechoslovakian manufacturer Tesla. Two different tape machines were used in the reception centre: one for recording the high-speed coded morse signals (at high speed) and one for playing them back at normal speed. The signal was then printed onto a paper strip by means of a HELL morse writer (undulator).   
Tesla Javornik tape recorder (1958)

Weight and dimensions
Part Dimensions Weight Designator Description
Sirius AB 271 x 150 x 70 mm 4.20 kg TI-466 AB Transmitter
Sirius D 190 x 72 x 50 mm 1.40 kg TI-485 Burst encoder
Sirius P 190 x 100 x 50 mm 0.95 kg TI-466 P Accessory box
PLUTO 190 x 100 x 50 mm 1.27 kg TI-462 A Receiver
Case 295 x 215 x 136 mm 1.85 kg - Carrying case
Total 295 x 215 x 136 mm 9.67 kg

  • Transmitter
    4-16 MHz (VFO)
  • Outut power
    80 W
  • Range
    1000-2000 km
  • Area
    West Europa
  • Receiver
    (PLUTO) 2-8 MHz and 4-16 MHz (VFO)
  • TI-466AB
  • TI-466AB 1
  • AB
  1. SIRIUS technical manual
    20 December 1959. Scanned August 2015 from faded original.

  1. Anonymous, SIRIUS spy radio set - THANKS!
    Devices kindly donated by anonymous former user. July 2015.

  2. Detlev Vreisleben, Photographs of accessory box
    Germany, 10 February 2005. Received August 2015.

Further information

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Crypto Museum. Created: Friday 31 July 2015. Last changed: Friday, 22 July 2016 - 14:14 CET.
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