I have been generating VE2IQ compatible waveforms stored as .WAV files
and making use of a constant amplitude envelope and raised cosine phase
transition. Last night I tested some MS100 generated signals with phase
transition times ranging from 5ms to 50ms. This latter version is quite
narrow with the transition taking up half the entire bit interval, and
sounds a little like PSK31 with a gentle warbling tone, although
obviously a very different signal.
On the perfect, noise free, WAV file 'Coherent' software has no trouble
locking up to the waveform even on the slowest transition. The next
step is to add a controlled amount of noise to the .WAV file and retest.
I think I already have a prog to do this, culled from work on signal
analysis a few years ago.
4 generated WAV files currently , each consisting of 80 seconds of
MS100, ET1 coded message of 1.3meg each. Interestingly, all four ZIP
up to a file just 20k - that's a serious compression ratio - so I can
send copies to anyone who is interested in playing with this, so far
experimental, scheme. It is difficult, though not impossible, to play
these .WAV files over the air using my LF transverter if anyone wants to
try off air reception.
Does anyone have a programme to repeatedly play .WAV files in a
continuous loop ? This will not be ideal for 'Coherent' data testing,
as there will be a discontinuity at the wrap round point that will
necessitate re-syncing, but is better than nothing.
Andy G4JNT
From DL2YHF
Claudio (IK2PII) for his contribution. I have to think about using a
four-quadrant multiplier, maybe this is another way to
produce the slow phase
shift. An I/Q multiplier is exactly what the 'original'
amplitude-shaped BSK
modulator uses. At the present time, I generate a kind of PSK
with "soft"
phase transitions using a simple sine function with a slowly
moving "phase
offset" to the argument, like >
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