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LF: PSK08 Tests

To: [email protected]
Subject: LF: PSK08 Tests
From: [email protected]
Date: Fri, 25 Feb 2000 14:34:21 GMT
Reply-to: [email protected]
Sender: <[email protected]>
Apologies if this has been sent twice, but I have a suspicion the firewall
software on the other EMail account is playing up and delaying things.

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

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