From: "Mike Dennison" <mike.dennison@rsgb.org.uk>
To: rsgb_lf_group@blacksheep.org
Date: Wed, 12 Jan 2000 09:50:28 -0000
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Subject: Re: LF: CFH (again!)
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G3YMC wrote:
> Mal mentions the problem of QRM from CFH - in case we hadn't noticed!  I
> suggest that the Rugby transmitter on 73.4, which has more or less put an
> end to realistic QSOs on that band, is similar both in function, purpose
> and power to CFH.  The noise sidebands we get from GBR are probably what a
> listener in VE1 would hear on 136!  If QSOs on 73 are limited to 11km on
> 73kHz when Rugby is on (congratulations Jim!) we are going to find it a
> bit hard going to work VE on 136!!

I strongly believe that the noise on the Rugby 73.4kHz transmssion 
is not merely a function of its strength. Most of us (outside the 
Midlands) had no trouble having QSOs on most of the band until 
about Spring 99. I could get 9+50dB on the Rugby signal and S3 
noise floor only a couple of hundred of Hertz away, but now the 
noise is over S9. 

This is either accidental - noisy oscillator, or (most likely) deliberate -
 spread spectrum or clever data mode.

The effect was first noticed by Roger, G2AJV, who spent hours 
trying to fix what he thought was a fault on his antenna when he 
could neither hear nor work people who used to be good signals. 
Dave, G3YMC, himself reported being puzzled not to hear signals 
that were prevously good. Later, I tried to work G3YXM for a second 
time and we were both surprised not to hear each other. The noise 
crept up on us as the band was used for amateur contacts only 
once every few months.

It is possible that CFH has some noise sidebands, but please don't 
assume that the present Rugby signal is typical of LF commercials.

At the risk of winding Mal up, the only really useful way to make 
QSOs on 73 these days is QRSs. This was used by myself and 
G3LDO to work GD0MRF at 400km+.


Mike, G3XDV (IO91VT)
http://www.dennison.demon.co.uk/activity.htm