[Lowfer] Poor LF propagation lately?

[Alan Melia]

Hi Both, I cannot resist my usual comment that there is not a "season" for
LF propagation.....only a season for comfortable listening. In fact
Trans-Atlantic propagation on 136kHz and 500kHz has been good over the last
few weeks that is a greater distance that you are probably shooting at (?)
Some of the best conditions across the Atlantic have been achieved in
summer.

There is very little of the excess night-time absorption due to
procipitation of hot electrons from CMEs and Coronal Hole flows, and in fact
the amount of disturrnabnce has been low. there may be one or two
possibilities that account for poorer than normal conditions over
intermediate ranges. One iis that I suspect, but have no expert back-up,
that during a long quiet spell such as we have been havingover the last 18
months the E-layer which is responsible for night-time skywave signals seems
to become increasingly transperent at these frequencies. This effect is more
noticable at less-than-maximum ranges where the signal is entering the
ionosphere at a higher angle.

A second possible cause is that the conditions are fairly stable. The
ionosheric shell is not being casued to ripple so much by solar wind impacts
and thus when the fading conditions are unfavourable you can get partial
canellation for long periods. This is often worse in periods of low
absorbtion because the higher mode (hop count) paths arrive at higher
strength. This effect is noticable on long paths like T/A but is not quite
so serious.

Daytime skywave is probably about 8 to 10 dB lower that it was when the was
more solar activity and dB lower than summer-time

Steve Dove's grabbers and plots may not be telling a true story at present.
I find his plots of DCF9 and HGA22 have shown drops in sensitivity that are,
to my mind confirmed by the drop in the average level of the daytime noise
plot. Last nights plot is particularly telling as an obviously local source
of noise normally 10 to 12dB above the base-line slid off the bottom of the
plot in the post midnight (UTC) period. I have noticed these periods over
the last month or so when Steve's plots do not seem to align with conditions
in the way they did for a lot of the last year. Making reliable measurement
over years in a way that they can be compared accurately is fraught with
difficulty and Steve does a great job in trying to keep the plots in line.

Interesting stuff this LF :-))

Best Wishes
Alan G3NYK