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Collections in Cryptology - Burst Encoders
Key mechanisms in computation...

The Burst Encoder enables an agent to take her time to compose a message, and once entered, to send that message on to her handler in a fraction of a second in order to avoid detection and interception. This device was normally used in conjunction with a radio, so that the transmission would commence and conclude too quickly for the signal to be traced or recorded. It could also be used over the telephone.

German Pocket Burst Encoder
Model RT3

Unit with the operator's cover open.

A cylindrical set of sliders, accessible to the user from the outside, allows him to set a sequence of 25 single digits from 1 through 0. The sliders are plastic and move across a slotted aluminum cylinder. The slider for digit "7" is colored red. All the others are white.

Unit with the front panel removed.

When a crank is attached and turned, each slider, in turn, closes a contact to activate one of the 10 active tracks on a brass commutator. Thirteen revolutions of the crank transmits all 25 numbers.

The brass commutator has 11 tracks across its width and 23 positions around its circumference. They are shown as "columns" and "rows" in the table to the right. Track "C" (at the left) is a common electrical connection. The non-contacting portions of the commutator are machined out, undercut in dove-tail fashion, filled with clear acrylic and then polished to a smooth finish.

The brass commutator is shown "rolled out" as it would appear to the operator with the cover of the unit removed. Contacts are colored dark; insulated areas are colored light.

Rotation of the commutator is downward, so the sequence of contact closures in the table runs from bottom to top.

Apparently, this is a modified Morse code of dots and dashes.

  • "Dits" are one bit long.
  • "Dahs" are 3 or 4 bits long.
  • Spaces are 1 bit.

Codes for each digit are repeated twice, separated once by 2 bits of spaces and again by 3 bits of spaces.

Only the code for "5" is proper Morse for "5."

The codes for the other numbers are Morse letters.

The repitition of the code for "4" (Morse "R") is offset by one bit. Perhaps this provides a recognizable "marker" to synchronize reading the pulses, since the sequence of rows 23, 1, 2, 3 (contact, no-contact, no-contact, contact, or "1001") will always signify the starting position for reading each of the transmitted numbers.

  C 1 2 3 4 5 6 7 8 9 0
  C 1 2 3 4 5 6 7 8 9 0
Morse W F V R 5 K B L G M

Russian Pocket Burst Encoder

The device consists of a 12-position disk which, when dialed with the included stylus, rotates a drum containing magnets to record numbers on a metal magnetic tape. No batteries are needed. The tape can then be played back through a separate device (currently unavailable) at a much higher speed.

Dial and tape unit locked together.

Dial and tape unit separated. Note the dialing stylus.
Russian Portable Burst Encoder
Datchik R-014D
Circa 1975

Keyboard, operator view.
Coder - U.S. Burst Transmission Group

Adapter, Keyer MX-4498/GRA-71, closed

Adapter, Keyer MX-4498/GRA-71, open

Coder, Tape MX-4495/GRA-71

Coder, Tape MX-4495/GRA-71

Coder, Tape MX-4495/GRA-71

Coder, Tape MX-4496/GRA-71

Magazine, Recording Tape MA-9/GRA-71

Brush and extra coder disk.

Keyer KY-468/GRA-71

Keyer KY-468/GRA-71

Brooke Clarke's Page

Peter McCollum's Page

Fred Chesson's Page (Manuals and Dates)

Antonio Fucci's Page (Photos)

AN/GRA71 Manual (Reproduction)

Circa 1966