An improved ´piccolo´ m.f.s.k. modem for h.f telegraphy

The Piccolo system of multi-frequency signalling has been in operation on the h.f. telegraphy network of the UK Foreign and Commonwealth Office for almost 20 years and has proved extremely effective. A new generation equipment has now been designed which is smaller, more reliable and more flexible than previous models, and incorporates a number of parameter changes and additional facilities suggested by experience and more detailed mathematical analysis. It allows operation in the ITA-2 code at 75 or 50 bauds, and in the ITA-5 code at a 110 bauds. The new parameters have enabled the bandwidth to be considerably reduced and the stability required from the reference source to be relaxed. The improved synchronizing system will pull in to synchronism in less than 3 seconds and remain synchronized over long periods of poor or lost signal. Special provision is made for operation on continuous cryptographically-protected data streams. The unit also includes a selective calling system and an optional error indicating code. Four telegraph channels can be frequency division multiplexed into a 2 kHz bandwidth. The availability of the system under poor-signal conditions is a considerable improvement over orthodox binary techniques.