Peter, G3LDO, and I transmitted beacons on 71.70kHz this morning
in an attempt to check whether our abortive tests of yesterday were
connected with the noise coming from Rugby. This frequency is as
far away as it is possible to get without getting QRM from the Decca
beacins.
I was able to hear Peter on my Marconi , but in the noise. Using my
1m loop antenna, carefully positioned, I could bring him up to 549.
Interestingly, even that far away in frequency from the Rugby
transmission I could bring up the noise by a significant amount by
rotating the loop.
The conclusion is that the Rugby RTTY transmission now has
significant white noise sidebands, extending up the band edges
(perhaps beyond). This ties in with reports I have had from others.
The noise is over 3kHz wide, even with the signal nulled to about S9.
Any useful work on the band will need the transmitter to be off for
maintenance. It is possible to have QSOs if you use the lowest
frequency you can without getting QRM from the Decca beacons - I
think 71.7 is about optimum - and use a directional antenna to null
out the Rugby signal.
I have posted on my web site a page showing spectrograms of
Peter's normal speed CW, and a comparison between the noise
levels at 71.7 and 72.1kHz (it's no wonder I didn't hear Peter
yesterday on 72.1). Note that these pictures are with the loop
antenna nulling out Rugby - so there is no question of Rx overload.
Peter will be listening for me tomorrow morning when I will be
beaconing between 0700 and 0745UTC.
Thanks to Alan G3NYK, Roger G2AJV and others for taking the
trouble to listen. (Roger, I will be listening between beacon
transmissions so give me a call if you hear me).
Mike, G3XDV (IO91VT)
http://www.dennison.demon.co.uk/activity.htm
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