Andre' Kesteloot
Fri, 25 Feb 2000 10:02:15 -0500

Talbot Andrew wrote:

> Now I know a few copies of PSK08 are out there I'll transmit this
> evening around 2000z.  Frequency will be 137.500 +/- 0.5 Hz,  chosen
> after careful consulation with this group  :-|)     Probably won't
> listen too much as no one has replied to say they can transmit yet and I
> know that three of those who have downloaded the code are listeners
> only.
> There is another modulation scheme suitable for this band that does
> allow constant amplitude, and hence highly efficient class D amplifiers.
> That is Continuous Phase Modulation (CPM), of which Minimum Shift Keying
> is an extreme example.   Listen to the transmission from Rugby on 16kHz
> or 22.1 kHz for an excellent example of a 100 Baud version of MSK.
> CPM is a very processor and memory intensive mode hence it is only now
> becoming popular, but at the speeds used at LF my feeling is that a PC
> could cope even if a 56002 EVM does not have the necessary memory
> capacity.  CPM is theoretically a few dB better than PSK in S/N terms,
> and in fact with the right coding is said to be able to get to within
> 0.7db of the Shannon limit.  Take this together with the constant
> envelope waveform and it could prove very exciting for very weak signal
> LF dxing.
> If anyone reading this has a more intimate knowledge of CPM please get
> in touch.  As far as I 'm concerned its all squiggles in a text book at
> the moment, and as for turning these into DSP code....
> Andy G4JNT
> Now ignore what follows :-|(
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