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Ferry van Eeuwen
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MFSK Background The history of MFSK over radio is not well documented. The earliest known system was developed in about 1935, and reported in Electrical Communication, 1937 by L. Devaux and F. Smets. This LMT system was a true Multi-Tone direct printing system, using a 7 x 5 dot matrix. It was similar in many ways to Hellschreiber, since it used the human pattern recognition ability to read the text, and the transmissions were not encoded. We now recognise this as C/MT-Hell, or Concurrent Tone Multi-tone Hellschreiber. 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. DTMF Probably the most widely known example of MFSK is DTMF - Dual Tone Multi-Frequency or "Touch Tone" signalling. DTMF was developed by Bell Labs, and is widely used in telephony - most people are familiar with the beeping noises that telephones make when the numbers are pressed. DTMF is a "two out of eight" system, using pairs of tones, from eight tones in two bands. It is used to signal numbers from 0 - 9, and four control signals A - D. One low tone and one high tone is transmitted for each code sent. Each pair takes a minimum of 50 ms. 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 UHF FM, is very popular for Amateur repeater control, and is also widely used for telemetry in alarm and security systems. MFSK software and lots of other digital modes software can be downloaded from the following URL: http://home.wanadoo.nl/nl9222/digisoft.htm Stream version 0.9 can handle MFSK8, but also MFSK16, PSK31, PSK63F en PSK125F. How many birds can you kill with one (freeware) stone?
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