Coquelet was a Multi Frequency-Shift Keying (MFSK) telegraphy standard,
used for transmitting textual messages over narrow-band short wave
radio channels. It uses more than two different frequencies (tones),
as opposed to the more standard Frequency Shift Keying (FSK) that uses only
two frequencies. Coquelet was developed by ACEC
in Belgium in the 1950s in order to avoid the common problems
of FSK over radio, such as selective fading and multi-path timing distortion.
It was used by the Armies and Police Services of Belgium, France, Algeria
and other countries
There are three variants:
- Coquelet 13, or Mk 1, using 2 tones from a set of 13 (13, 20 baud)
- Coquelet 8, or Mk 2, Synchronous MFSK, using 2 tones from a set of 8 (20, 26 baud)
- Coquelet 80, like Coquelet 8 but with Forward Error Correction (FEC) (20, 26 baud)
The name COQUELET is the French word for GRID.
The system works by sending two different tones in sequence (one after the other)
for each character from the ITA-2
With Coquelet 13,
the first tone was taken from a set of 8 different tones known as Group I,
whilst the second tone was selected from 4 different tones, known as Group II.
Each tone lasts 75 ms, resulting in baud rates of 13.3 and 20 Bd, less than
half the speed of Baudot (50 Baud) .
The upper table above show the organisation of the characters in the
Coquelet table when the machine is in letters-mode (LTR).
The lower table shows the characters that are used in figures-mode (FIG).
When ACEC introduced the first teleprinters
and cipher machines that used Coquelet 13,
they also developed interfaces that translated Coquelet into
Baudot (ITA-2) and vice versa.
In fact, Coquelet uses the ITA-2 table as its basis, and the machines
were constructed in such a way that messages could be stored on
standard 5-level paper tape, using the Baudot-Murray code.
Within the ITA-2 standard,
each character is represented by 5 bits.
The first three bits are represented by one of eight tones from Group I
(23=8), whilst the last two bits are sent as one of four
tones from Group II (22=4).
When there is no activity (idle), tone number 0 is sent.
The table above shows how the Coquelet 13 tones are translated to the ITA-2 bits.
- 1052 Hz
- 812 Hz
- 842 Hz
- 872 Hz
- 902 Hz
- 932 Hz
- 962 Hz
- 992 Hz
- 1022 Hz
- 1082 Hz
- 1112 Hz
- 1142 Hz
- 1172 Hz
The Coquelet standard was used in the following countries:
- Rhodesia 1
- Zimbabwe 1
- Olivia MFSK
- CIS-36 MFSK, a.k.a. CROWD-36
- XPA and XPA2
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© Crypto Museum. Created: Wednesday 19 November 2014. Last changed: Friday, 23 February 2018 - 22:11 CET.