Topband: signal peaking two hours before sunrise

[Nick Hall-Patch]

After the thread concerning signal peaks on 160m a couple of hours before
local sunrise, I decided to look at some of my signal strength recordings
of medium wave broadcast signals from the other side of the Pacific. The
system was described in the Topband Anthology, Volumes 1 and 2, and some of
the results are referenced there and in some of Bob Brown's articles.  A
fuller treatment is due to appear in QEX at some point.

The two stations monitored are HLAZ-1566 from Cheju Island, S. Korea and
4QD-1548 from Emerald, Queensland, Australia.   The analysis is queered by
the fact that HLAZ beams its signal towards here from 1230-1345 UTC, while
Victoria sunrise is presently around 1600UTC.  However, even correcting for
the transmitter boost at this time, it does appear a signal peak has been
occuring around 1300 UTC fairly often in the last few weeks.  The peak is
only occasionally stronger than any sunrise peak that occurs on those
mornings however.

4QD's signal is a tough one to dig out due to sideband splatter from
domestic station on 1550 kHz, but  last  season, minor signal peaks have
been observed in the 1300-1400 UTC period especially in February.  Those
minor peaks are also occurring this season, though usually with a similar
peak near local sunrise.

The point I'd like to make is that, at first glance, these peaks hours
before sunrise didn't seem to be so frequent when I started monitoring in
the '97 - '98 season, so perhaps the state of the solar cycle has some
influence on their occurrence.  (Mind you, in that first monitoring season,
sunrise peaks for 4QD were also unusual in the winter months; they are more
common now. HLAZ sunrise peaks were quite common in the winter during that
season; the pre-sunrise peaks not so much)  

Keeping in mind that my observations are based on a quick scan of the data
summaries from past seasons, do those who are observing 160m signal peaks
earlier than sunrise recall whether they're more frequent now than a few
years back?

As always, please note that local ground sunrise is used as a reference
point.  The real action takes place when the sun starts to shine on various
ionspheric layers, usually a few minutes before local sunrise.  (But what
is the mechanism influencing peaking of signals two hours before local
sunrise?  It's not midnight at the center point of the path between Asia or
Australia and here)

Best wishes,

Nick VE7DXR




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