Quote:
Originally Posted by Radio Wrangler
There was a programme to try to pack more PMR channels into limited bandspace back in the Early 70s. The Woolfson foundation was the sponsor and it involved Gosling and Macario. Their approach was to change from FM in 50kHz/25kHz channels and use SSB. One tool used was pilot-controlled companding, but the difficulty was frequency correction to get a good natural sounding voice. THe gear had to be simple enough to be affordable. A friend was doing his Phd in amongst that bunch.
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I recall something similar being tried in the US on their 220MHz band: it involved a curious digitally-created signal which, when presented to a discriminator produced the traditional FM-style low-DC component which varied in sign around the mid-point depending on whether the receiver was on the high or low side of correct. This was then used to control a locally regenerated carrier and fed to a more-traditional SSB detector.
It was quite effective but at low signal-strengths the discriminator-signal became jagged with noise and the 'CIO' unlocked. So overall the performance was no better than FM except that it occupied a narrower bandwidth (10KHz rather than the standard 20KHz channels which the US uses).