G3KEV said
Tell me Rik, why is there no qrss(LMCW) when the band is noisy like lots of
qrn/static about.
It should not be a problem if you can read signals 20 db below the noise.
My ANSWER after monitoring and experimentation with spectran is that the qrn
chops the long dashes and you cannot be sure if it was lots of dots. This does
not happen with normal cw because one can read words in between the crashes and
conduct a qso even with a weak signal.
When I lived in Sierra Leone in the 60's I was persuaded by W1BB to
go on 160m. This was done using a large VHF mast to support a 40m
high antenna. Getting out using low power (we were allowed a maximum
of 10w input to the PA) was not problem but receiving was something
else. You have to experience 160m QRN in the tropics to know just how
bad it can get.
We (9L1TN and myself) found that stations who sent CW slowly got
through the noise much better. The reason being that a crash of QRN
would only take out part of a character at slow speeds while it could
delete a complete word or more at higher speeds. We were criticized
in one of the magazines for working at 6WPM but they did not
understand our problem.
During the early experiments on 73kHz the same problems arose - very
weak signals in the presence of QRN. Again, slow CW proved more
effective than faster CW in QRN.
Any one who has looked for very weak signals using QRSS is aware of
what QRN looks like. The QRN pulse creates a band across the screen
obliterating the signal for the duration of the pulse. The time width
of the pulse depends on the scanning time and the receiver AGC. It
is essential that, when receiving weak signals in the presence of
QRN, you have control of the AGC and it should be set to FAST or OFF.
If a QRN pulse of several milliseconds chops a bit out of a dot or a
dash the readability is normally unaffected. With frequency shift
keying methods the effect of QRN is even less apparent.
I have some excellent screen shots of QRP Italian stations showing
good readability in the presence of QRN.
I have no problems with fast CW. If the signal strengths are
reasonable then fast CW is fine - the speed should be appropriate for
the circumstances.
--
Regards, Peter, G3LDO
<[email protected]>
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