Thanks to Marcus, who pointed out that the transmission is, as I should have
known, and ISB transmission with data two channels, one on each sideband.
When I listened on Friday evening only the lower sideband channel was in
use, which misled me. Tonight both were in use and at 1927z the upper
sideband went into idle for 2.5 mins, and by 2030 only the upper sideband
channel was in use. When both are in use there are pairs of 'noise'
sidebands visible at some distance from the main signal, for instance these
were visible at 72.61 and 72.37kHz tonight. Thus I suspect
that the 'width' of the noise that we hear when trying to work 73k is
probably a function of how busy that channel is....whether both sideband
channels are in use. It may be that a couple of years ago it was mainly used
on just one sideband.

That deals with the my thoughts on the noise. The 100Hz lines we can see are
referenced to the 'subcarrier' at the middle of the lower sideband 100Hz
shift signal. ( I thought this was a symetrical carrier shift signal.) It is
still drifting around like mad tonight. The lines remain accurately 100Hz
part far out from the signal, and as they move away from the carrier their
amplitude is 'modulated' by another envelope, so that strong lines seem to
appear mostly in pairs, with one or sometimes two intermediate lines very
weak. I still cannot understand why they seem to drift slowly, because the
envelope to the sideband data transmission seems to be stable. I can only
assume that the modulation is a phase shift variant and the apparent shift
of the sub-carrier is is a function of the data. It could of course still be
that they have a bug in the baseband modulator, but I now doubt it.

I think I will slide away into my hole again and not bother rattling the RAs
cage just yet. Thanks for the comments Marcus....just what I was
seeking....support or otherwise.

I suspect I may devote my efforts to 8kHz now at least the Rugby station
(GBR) is an octave away!!

73 de Alan G3NYK
[email protected]