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Clandestine spy radio transmitter

TI-466 AB, or SIRIUS AB, or just AB, was a spy radio transmitter, developed in Czechoslovakia between 1958 and 1962 by Správa 6 1 for the secret state police (StB) and Správa 1 (espionage) for use in clandestine operations in the West European theatre. The transmitter is part of the SIRIUS radio station, has a frequency range of 4-16 MHz and delivers approximately 80W.

The image on the right shows a typical AB, which measures 27.5 x 15.5 x 6.5 cm and weights: 4.2 kg. Contrary to the other items of the SIRIUS radio station, which are all painted grey hammerite, the case of the AB is black.

The transmitter has a built-in mains transformer (PSU) that is suitable for the most regular mains voltages around the world. The PSU also powers the matching PLUTO receiver, which should be connected to the DIN socket at the left side. At the front is a 6-pin socket for connection of a tape-based TI-485 (DÁVAČ) burst encoder.
TI-466AB transmitter

Unlike most other spy radio transmitters of the same era, nearly all of which are crystal-operated, the TI-466 AB transmitter is free-running, allowing it to be used on any frequency in the 4-16 MHz range. In order to avoid any inaccuracies, the device has a built-in crystal calibrator.

Development of the AB started in 1958, a few years after the introduction of the PLUTO spy radio set, and took several years before the first sets were delivered in 1962. During its lifetime, it was modified and simplified several times. Once the sets were decommissioned in the early 1980s, all but one were destroyed. It is likely that the one featured here is the only surviving example. The SIRIUS transmitter was succeeded in 1966 by the SIRIUS III transmitter (TI-526) with separate PSU.

  1. Správa 6 refers to Government Department 6: Communication Technology.

TI-466AB transmitter
Overview of connections and control of the TI-466 AB
Frequency and or code-number engraved in the crystal
Crystal contact pins
Inserting the crystal
Crystal fitted to the TI-466AB
PLUTO receiver, SIRIUS transmitter and (prototype) burst encoder
The image below shows the various controls and connections of the TI-466 AB. Operating the device is pretty straightforward and requires only limited knowledge of its operation. Before connecting it to the mains, the voltage caroussel at the top left should be check for the proper AC main voltage. The PLUTO receiver should be connected to the 6-pin DIN socket at the left, and the DAVAC burst encoder to the rectangular 6-pin socket at the front right of the transmitter.

The transmitter has two frequency ranges: (1) 4-8 MHz and (2) 8-16 MHz, and is freely tuned to any frequency within these two ranges. A built-in calibrator with an external crystal and an earpiece can be used to check the frequency scale. The crystal should be in the 120kHz range.

Crystal fitted to the TI-466AB
DIN socket for connection of the receiver
Frequency adjustment
Crystal socket
Antenna tuning
Antenna coupling and PA current meter
Mains power socket
Block diagram
The image below shows the block diagram of the AB [B]. The main oscillator is free-running and is visible at the center. It produces the base frequency (f0) in the range 2-4 MHz, which is then doubled to 4-8 MHz (range 1) and (optionally) doubled once more to obtain 8-16 MHz (range 2).

The transmitter is designed for operation in combination with an external high-speed morse recorder, also known as a burst encoder, which is shown at the top left. The signal from the burst encoder is first re-shaped and amplified, and then used to enable/disable the transmitter.

The TI-466AB has two sockets for the connection of peripheral equipment: a 6-pin 270° female DIN socket for connection of the receiver, and a 6-pin rectangular female socket for connection of the burst encoder. Below is the pin-out when looking into the sockets from outside the case.

  1. ?
  2. 170V AC (HT)          
  3. 0V AC
  4. 6.3V AC (LT)
  5. ?
  6. ?
Burst encoder
  1. Modulation (+)
  2. LT (6.3V AC)
  3. LT (6.3V AC)
  4. HT in
  5. HT out
  6. Modulation (GND)
  1. 6F32
  2. 6L43
  3. REE30A
  4. CK6111
  5. DM70
    Tuning indicator
  6. CK6111
  7. EF732
  8. 11TA31
  9. 3-9V, 0.175A
  • Frequency
    4-16 MHz (two ranges: 4-8 MHz and 8-16 MHz)
  • Oscillator
    2-4 MHz
  • Modulation
    F1 (FSK), later modified to A1 (CW)
  • Deviation
    2kHz ±160 Hz
  • Output
    60-75 W
  • Antenna
    6-8 m
  • Stability
    10-6 / °C
  • Acuracy
    ±160 Hz @ +10°C to +30°C
    ±640 Hz @ -10°C to +25°C
    ±1240 Hz @ -20 to +60°C
  • Drift
    ±20 Hz per 20 seconds after 10 minutes warming up
  • Muting
    30dB (during calibration)
  • Mains
    110/120/210/220 V AC (50-60 Hz)
  • Session
    15 seconds (25 seconds max)
  • Interval
    Minimal 1 minute between two sessions
  • Sessions
    20 (max)
  • Calibration
    2 minutes (max)
  • Temperature
    80°C (max) protected
  • Earpiece
    50 Ohm (calibrator output)
Power consumption
  • PA
    28W (without pre-heat)
  • Pre-heat
  • Calibration
  • Transmit
  • Receiver
  1. SIRIUS technical manual
    20 December 1959. Scanned August 2015 from faded original.

  2. TI-466AB (transmitter) circuit diagrams
    20 December 1959. Scanned August 2015 from faded original document.
  1. Anonymous, SIRIUS spy radio set - THANKS!
    Devices kindly donated by anonymous former user. July 2015.
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