Bulletins from the Pacific Packet Radio Society - page 144

Den Connors KD2S

The Amateur Radio Service will be undergoing a transformation as personal computers bring the need for high speed digital communications into the ham shack. The modems now heard on the air will be woefully inadequate to provide bandwidth-efficient data transmission. This has led a number of amateurs to look into synchronous modulation techniques, and in particular, minimum-shift keying (MSK).

MSK was first patented as a "Minimum-Shift Data Communication System" in March of 1961 by Melvin Doelz and Earl Heald of the Collins Radio Company. Known alternately as fast-frequency shift keying (FFSK) in the early literature, the technique provided the minimization of bandwidth the researchers were looking for, using simple frequency-shift keying. The price they paid was in the complexity of the synchronous demodulators.

MSK can be described alternately as frequency shift keying with a fixed modulation index of 0.5, or as phase-shift keying of a digital signal with Gaussian pre-shaping of the signal input to the modulator. This very cryptic non-explanation may be clarified by digging into the available literature.

General Articles -

There are several articles which can give a general overview of the technique. Pasupathy presented MSK in an easy-to-read format for the IEEE in \PAS79}. A more complete technical presentation was done by Rudi DeBuda \DEB72}9\DEB74}. Morais and Feher \MOR791 introduce investigations of the effects of noise on MSK, and Gronemeyer and McBride fold in similarities of MSK and PSK in their 1976 article \GR076}.

\DEB72} R. DeBuda, "Coherent Demodulation of Frequency-Shift Keying with Low Deviation Ratio", IEEE Transactions on Communications, Vol. COM-20, No. 6, pp. 429-35, June 1972

\DEB74} R. DeBuda, About Optimal Properties of Fast Frequency-Shift Keying", IEEE Transactions on Communications, Vol. COM-22, No. 10, pp. 1726-7, October 1974

\MOR79} D. Morais & K. Feher, "Bandwidth Efficiency and Probability of Error Performance of MSK and Offset QPSK Systems", IEEE Transactions on Communications, Vol. COM-27~ No. 12, PP. 1794- 1801 , December 1979

\GR076} S. Gronemeyer & A. McBride, "MSK and

Click for Original Graphic Image of this page.

Previous Index Next