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LF: First steps towards MSK for "fast" communications on LF

To: RSGB LF Group <[email protected]>
Subject: LF: First steps towards MSK for "fast" communications on LF
From: Wolf DL4YHF <[email protected]>
Date: Wed, 29 Dec 2004 20:20:58 +0100
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Greetings all,

Some will remember the recent ideas about using MSK (minimum shift keying) on LF as a PSK31-like mode for "fast keyboard-to-keyboard" communication with minimum overhead.
There is a preliminary implementation of MSK in Spectrum Lab, available
on my website now: (http://people.freenet.de/dl4yhf/spectra1.html).
If someone would like to play with it, it works "almost" like PSK31 or
PSK08, in fact it uses the same codeset and bit encoding rule. The
decoder leaves plenty of room for improvement though (at the moment, it
is a robust incoherent decoder - not as good as PSK31 yet but it works.
You don't need a "linear" transmitter for it, due to the constant
envelope waveform, but -at the present time- you will need audio keying
because the MSK signal is generated with the soundcard.
Like Bill, VE2IQ, I tried to send the MSK keying signal through an
output line of the serial port, but the jitter on it is dreadful - no
chance to switch the frequencies of a DSP this way.
To activate the "digimode terminal" in MSK mode, select
Quick Settings  |  predefined digimodes | MSK 31 or MSK 08 .
Then, in the dialog window, enter the audio frequencies (I prefer something around 2 kHz, which makes sure the audio harmonics are outside the SSB bandwidth).
It would be nice to do some initial on-air tests soon; skeds can be
arranged anytime since I'm on holiday - or look for a funny looking MSK
idle tone, which consists of THREE lines on the spectrogram, with the
center line being stronger than the two outer lines. The outer lines are
spaced 31.25 Hz for MSK31 and 8 Hz for MSK08 (like those in (B)PSK31 and
PSK08 .
When QRV at DF0WD, I will call on 137.5 kHz if the frequency is clear.

73, Wolf DL4YHF .



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