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Tape-based morse burst encoder

MĚSIC (moon) was a tape-based burst encoder that was intended for sending messages in morse code at very high speed. It was developed in mid-1960s in Czechoslovakia by Správa 6 1 for use by the secret intelligence agency (StB) and Správa 1 (espionage). It was used in combination with the SIRIUS III spy radio set and was the successor to the DÁVAČ burst encoder that was supplied with the original SIRIUS set in 1962. The fully transistorised device is also known as SIRIUS D.

The device is only marginally different from its predecessor DÁVAČ, but has a different layout of the number-keys. Furthermore, it has a different socket for connection to the transmitter. The endless tape is in a triangular compartment on top of the device (at the far left), whereas it was located at the left side on the DÁVAČ recorder.

In addition, the keys are somewhat recessed so that they can not be pressed accidently. The numerical keys (0-9) are used for entering a pre-coded numerical message. The X and Y keys are used for START and STOP respectively.
TI-485 burst encoder (prototype)

The device can play back pre-recorded messages consisting of 200 groups 2 in just 15 seconds. Two smaller buttons, just above the keypad (barely visible here) are for the Record and Erase functions. The mechanical tape recorder at the left can further be controlled by means of two rotary knobs along the front edge. The one on the left is for rewinding the tape. Unfortunately, the case is missing from the device shown here. Please contact us if you have any further info.

  1. Správa 6 refers to Government Department 6: Communication Technology.
  2. In this context, a group consists of 5 numerical digits (0-9).

TI-485 burst encoder (prototype) Rear view Close-up of the tape section Operating the tape mechanism Operating one of the two buttons Top view Key pad and switches Connector
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TI-485 burst encoder (prototype)
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Rear view
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Close-up of the tape section
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Operating the tape mechanism
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Operating one of the two buttons
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Top view
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Key pad and switches
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The diagram below shows the location of the controls and the connector. Please note that the device is normally enclosed by a grey hammerite metal case, sith only the knobs and buttons accessible from the top. For normal operation, there should be no need to remove the device from its case. The tape is endless and should only be replaced when it is worn out or broken.

The diagram below shows the location of the various parts when looking at the assembly from the bottom. At the centre is the motor that drives the mechanics. At the right is the coded drum that consists of 10 notched rings, each of which represents a numerical character in morse code.

Although MĚSIC is mechanically different from its predecessor, DÁVAČ, the electronic circuit is identical. It can be downloaded below, along with a full description of the device in Czech/Slovak. The tape is erased by applying a constant Direct Current (DC) to the recording head, whilst the tape is running. Recording is done by applying an intermittend DC to the head. In playback mode, the signal from the head is amplified, and then passed on to the transmitter.

Side view Bottom view Close-up of the coded drum Wiring detail Electronics detail Electronics detail Close-up of record/playback head
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Side view
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Bottom view
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Close-up of the coded drum
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Wiring detail
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Electronics detail
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Electronics detail
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Close-up of record/playback head

Unfortunately, the MĚSIC device featured above, came without the original enclosure. The image below shows what the device looks like in its original case. The photograph was made by Detlev Vreisleben in the Police Museum in Prague as part of a complete SIRIUS III spy radio set [3].

MESIC burst encoder in the original enclosure. Photograph kindly supplied by Detlev Vreisleben [3].

 More about the SIRIUS III spy radio set

  • TI-485
  1. TI-485 'DÁVAČ' technical manual (with circuit diagram)
    20 December 1959. Scanned August 2015 from faded original.
  1. Anonymous, MESIC burst encoder - THANKS!
    Device and documentation kindly donated by anonymous former user. July 2015.

  2. Louis Meulstee, Wireless for the Warrior, Part 4 Supplement
    Forthcoming. Accessed August 2015.

  3. Detlev Vreisleben, Photographs of SIRIUS III radio set
    Germany, 10 February 2005. Received August 2015.
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Crypto Museum. Created: Sunday 02 August 2015. Last changed: Saturday, 01 July 2017 - 11:48 CET.
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