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
|
