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 DWS Chief Engineer Harold Robins OBE (who worked for MI6 from 1939 - 1946, and DWS from 1946 to 1971). Donald Bailey and Dennis Ralphs were development team project leaders. The system was first demonstrated at an Institute of Electrical Engineers exhibition in London in 1963, where it aroused much interest.
The original PICCOLO specification
- This system was an amplitude modulated system using a carrier and with one sideband removed. The tones used were between 330 and 660 Hz, spaced at 10 Hz intervals, and operating at 10 baud.
The first tests were at Crowborough in Sussex, where an underground high-powered radio station had been built in the Ashdown Forest. This station was built to send propaganda to Germany during WWII. Two way communications was first established with Delhi in 1962, with Beirut in 1964 and then with Singapore in 1965, using the 32 tone system, one tone per letter of the alphabet! (Actually 33 tones, as an idle tone was used to maintain synchronism). The system proved extremely successful, and communications between Britain and Singapore often continued for an hour after standard teleprinter links had faded out. To quote from David White G3ZPA, who worked with the 33 tone system at the time:
"I was allocated to take part in the Singapore tests from our London station. It was amazing,
it was so superior to conventional radio teleprinter systems as almost to be beyond belief,
and was quickly used for regular traffic. When we opened the circuit at 6 A.M. every
morning, the Piccolo would give solid copy immediately,
but the RTTY was so poor it was not till 7 A.M. before it was usable for traffic. It was the same
in the evening, because after 6.30 P.M. the RTTY would fade out to become unusable, but the Piccolo
still kept giving solid copy for another hour. The amazing thing was that we could no longer hear
the signal on the receivers, but the tone oscillator detection system could still produce an S9 signal
so long as it could detect it even though the signal was under the noise level.
"It was so good that we quickly adapted all 64 radio stations around the world to change over from RTTY and Morse until by 1967 Piccolo had taken over. It handled all government diplomatic traffic for the next 22 years, until it was decided change to an even narrower band system, that was even faster than the 100 baud 33 tone Piccolo, which was expensive and needed dedicated Piccolo technicians to maintain it. Existing radio teleprinter engineers had no knowledge how to maintain it".
The newer, faster system David mentioned was the 6 tone Piccolo Mk 6. The equipment was smaller and cheaper to manufacture. David quotes 100 baud for the 33 tone system, but of course that was the speed of the teleprinters, 100 bit/s, while the radio link ran at 10 baud. The Piccolo engineers and technicians were trained at the SOE Headquarters at
Poundon House in Buckinghamshire.
Piccolo Mk 1 to Mk 5 were all 33 tone systems with no error correction. The system was so robust that none was needed, and tests in 1968 comparing Piccolo with the new experimental SITOR system (known to Amateurs as AMTOR) showed that when copy became difficult the SITOR link slowed down or stopped, while the Piccolo link continued at full speed with just the occasional error.
- Since the system was generally used with five character cypher groups, errors were easy to spot.
- Later systems were designed to be adapted for error correction, but it was not heavily used for most short hop telex transmissions
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 final Piccolo transmission took place on the 4th July 1993, and the whole of the U.K. Government's radio transmission system on high frequency was then scrapped.
- One remaining original 6-tone Piccolo system remains in working condition at the Bletchley House museum, lovingly restored by David G3ZPA, who kindly provided much of the historical information about Piccolo.
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.
The most well known versions can be summarised as follows:
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