The system was developed by the company "Le Materiel Telephonique", and trialled during 1937 on the path from Algiers to Paris, (1300 km) on 12.2 MHz. It is not known whether the system went into commercial service, but it and the LMT company were probably war casualties.
1 | 2 | 3 | A | 697Hz |
4 | 5 | 6 | B | 770Hz |
7 | 8 | 9 | C | 852Hz |
* | 0 | # | D | 941Hz |
1209Hz | 1336Hz | 1477Hz | 1633Hz | - |
DTMF is widely used on telephone circuits, but is little used on HF
due to problems such as stability and false detection on
noise. DTMF works well on VHF and UFH FM, is very popular for Amateur repeater control,
and is also widely used for telemetry in alarm and security systems.
Coquelet technology was well documented in the designers' house magazine,
ACEC REVUE No 3-4, 1970, in the article "Les T�l�imprimeurs,
T�l�chiffreurs et Transcodeurs ACEC - Syst�me Coquelet".
This important paper includes an excellent analysis of why it is
advantageous to limit the number of symbols per character to one or two.
Coquelet was conceived as an electromechanical system, using tuned reeds
to generate the tones, and the same reeds as receiver filters. Because the tones
were in two sets, low and high, one for each tone of the pair, sync
could be recovered
directly. Coquelet was designed to operate directly with existing ITA2
teleprinter equipment, so ran at the equivalent speed. The original system was
asynchronous (i.e. stop-start; there could be gaps between tone pairs with
hand sent text), and the equipment converted the signals directly from and
to conventional teleprinter asynchronous signals. ACEC also manufactured
ITA2 to Coquelet two-way converters.
Coquelet used tones spaced at three times the baud rate. The tones are in two groups,
low tones spaced 30 Hz apart from 812 to 1022 Hz are used for the first symbol of each
symbol pair that defines an ITA2 character, and define three bits of the character.
High tones spaced 30 Hz apart from 1082 to 1172 are used for the second symbol,
and the remaining two bits of the character. The symbol sync is implicit in the
different
tones used for the first and second symbols of the pair.
The first tests were at Crowborough (a photograph is extant). Two way communications
was first established with Delhi in 1965, and then with Singapore, using the 32 tone
system, one tone per letter of the alphabet! The system proved extremely successful,
and communications between Britain and Singapore often continued for an hour after
standard teleprinter links had faded out.
Initial transmissions were on AM, soon to be followed by SSB. The 6 and 12 tone
systems
were introduced in the late 1970s to further save bandwidth. The 6 tone system is
still in limited use today. Current equipment is made by Racal.
Like Coquelet, Piccolo is a tone sequential-tone system, using six or twelve
tones,
however Piccolo was from the outset a completely electronic system, with the
exception of the symbol clock, which was at first motor driven!
The early 32 tone version is well documented in the paper "Multi-tone
signalling system employing quenched resonators for use on noisy radio-
teleprinter circuits, published by J.D. Ralphs et al, Proc. IEE Vol 110 No.
9,
September 1963.
This paper describes the use of quenched lossless LC filters for reception
and tone generation, and has an interesting discussion of how to achieve
orthogonal signalling in a non-coherent FSK environment. The discussion is
in the time domain, and nicely parallels modern frequency domain arguments
about tone spacing, which reach the same conclusions in different language.
The early Piccolo system related each of the ITA-2 characters to a single tone,
so operating at 10 baud achieved a remarkable 100 WPM. Like Coquelet, the
later Piccolo systems are two-tone techniques, i.e. transmitting sequential
tone pairs. Synchronism is achieved in all systems by 10% AM modulating the
transmitter with a character rate square wave.
Unlike Coquelet, Piccolo uses the minimum tone spacing for orthogonal
detection (spacing = baud rate) and has always used electronic tone
generation. The integrate and dump detection system allowed this level
of performance, and the receiver filters were also used as triggered
oscillators to generate
moderately phase synchronous tones. Many versions of Piccolo
exist - the most well known versions can be summarised as follows:
COQUELET
The Belgian "Rooster" was developed by ACEC from the 1950s to provide improved text
transmission. Coquelet attempted to combat the problems that plagued RTTY at the time,
and do still - selective fading and multi-path timing distortion. Little is known of its
early history.
It was largely used by Belgian, Algerian and French Customs and Police services. There
are three forms of Coquelet, known as Coquelet 13 or Mk1, Coquelet 8 or Mk 2, and
Coquelet 80. All three systems are two-tone systems, i.e. transmitting sequential
tone pairs. They can be summarised as follows:
Name
Type
Tones
Data Rate
Code
Coquelet 8
Sync MFSK
2 of 8
20, 26 baud
ITA-2
Coquelet 13
Async MFSK
2 of 13
13, 20 baud
ITA-2
Coquelet 80
Sync MFSK with FEC
2 of 8
20, 26 baud
ITA-2
PICCOLO
Work on developing a robust teleprinter system for diplomatic service use started at
the Hanslope Park offices of the Diplomatic Wireless Service, part of the
British Foreign and Commonwealth Office, in about 1957. Piccolo was developed first by
Harold Robins OBE (who worked for MI 6 from 1956 - 1958), assisted by Donald Bailey
and
Denis Rouse.
Name
Type
Tones
Data Rate
Code
Piccolo Mk 1
Sync MFSK
1 of 32
10 baud
ITA-2
Piccolo Mk 6
Sync MFSK
2 of 6
20 baud
ITA-2
Piccolo Mk 12
Sync MFSK
2 of 12
40 baud
ITA-5