Message-ID: <2000050919121868199@zetnet.co.uk>
Date: Tue, 9 May 2000 19:12:18 +0100
To: rsgb_lf_group@blacksheep.org
From: "Peter Dodd" <g3ldo@zetnet.co.uk>
Subject: LF: Re: QRN and QRSS
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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

<g3ldo@zetnet.co.uk>