Hello group,
Just did a few tests (off-air) using a slow variant of PSK31 which could be
called PSK10, PSK05 etc.
Instead of the signaling rate of 31.25 symbols/second from G3PLX's original
PSK31, I used only 10 or 5 symbol/second. This reduces the bandwith to 1/3rd
or 1/6th of the original PSK31 signal, and thanks to the nice coding scheme
used in PSK31, the character transmission speed is still acceptable for a
'real' QSO.
( For those who are not familiar with PSK31:
It uses a code set called 'Varicode',
which uses fewer bits for frequent letters like 'e'
than the others, similar to the Morse code.)
To test the effect of the reduced symbol rates, I added white noise to the
signal and compared the decoded text with the original PSK31. I decreased the
signal/noise ratio until the decoded text became undetectable.
The results were as expected: Using "PSK10" instead of "PSK31", the noise
could be increased about 3 times in amplitude for the same detection quality.
However, if you want to test the 'slow PSK31 variants' on air. Because all
PSK31 programs I had did not support other symbol rates than 31.25sym/sec, I
modfied the PSK modulator and detector from WinPSK (by AE4JY) and stuffed
them into Spectrum Lab.
I just uploaded a new release of SpecLab (V1.63) with a built-in 'digimode
terminal'. It is available at www.qsl.net/dl4yhf/spectra1.html. Beta testers
are welcome. Bug reports please to [email protected]. How about some 'QRPP'
tests, Geri ?
------------ snip ------------
Drifting frequency of DF0WD's CW signal:
The problem is a result of the poor stability of the main oscillator in my
old Icom IC706. The fan blows warm air from the final amp towards the 'master
crystal'. I watched the Loran lines yesterday, and found them 'wandering'
around the sreen for about 30 seconds after one over (using only normal CW
here).
I thought about buying a 'TCXO' for the IC706, but the cost of about 120euro
for that tiny piece of PCB kept me off. Any better ideas ?
----------- snip -----------
73's Wolf (DL4YHF, qrv on LF only from DF0WD).
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