From Dave G3YMC
At the expense of increasing the digital divide on 136!!
The 136kHz band is slightly different from other hf bands in so far that it is
rather narrow, and there is a far greater conflict between the various modes of
transmission which are all fighting for space. To date we have had CW, QRSS,
BPSK and associated data modes, and now we are getting slow voice which requires
its own space. It is therefore always going to be difficult to provide enough
space for all users without mutual interference. The band plan which has been
worked out (admittedly a couple of years ago when some of the modes were not
active) was produced in good faith, and like the band plans on the higher bands
it makes life easier for us all if they are followed.
Up to recently most of the slow CW and data communication has indeed been
confined to their allocated parts of the band, and this has worked well, with
very little mutual interference between normal CW and the data modes. However a
conflict in situations both here and in Canada/USA threatens to upset this
relationship. There is an analogy between unwanted mixing of SSB and CW on hf,
whereas an SSB QSO can be conducted with CW interference in the background,
whereas the SSB signal gives significant interference problems to the CW
operator. In a similar way, users of slow CW and other spectrogram modes have
so much more selectivity in their digital processors that they are not usually
effected by signals 10s of Hz away unless these are very strong local ones. The
normal CW op, using normal receive filters assisted with audio filtering, can
find such adjacent signals disasterous. And the inability to identify in normal
CW and respond when transmitting such digital modes seems rather unsatisfactory.
I would strongly urge all operation on slow CW and other data modes to continue
to be made in the recognised parts of the band, and leave 136.0-137.4 for normal
CW. There are indeed times when this part of the band may be quiet and unused,
but at busy times (eg Sunday mornings) it is barely adequate. If it is possible
to get Jack to move his test transmissions out of this section it would be
appreciated - although Jack's signal is unlikely to affect a normal CW operator,
the unintentional QRM caused by an operator who does not know he is there could
be a problem. Hopefully there will not be a repeat of the events of Saturday
night.
73s Dave G3YMC (on the analogue side of the digital divide...)
[email protected]
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http://ourworld.compuserve.com/homepages/sergeantd
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