If it may be any help in knowing what to expect from the eclipse, I can
summarize some of the effects of the 1995 total solar eclipse over North
America.
That one entered the US from Mexico over western Texas, tracked through
Oklahoma, over southeast Kansas, through Missouri, then on up across the
northern Midwest. Given that I live in the southeastern US, this put the
path of totality about 450 km to my northwest. Extending that same line
beyond the ground track another 450 km (give or take), one finds Fort
Collins, Colorado, the home of time station WWV at five convenient spots in
the HF bands, plus WWVB at 60 kHz.
Hence, totality fell dead-center between my QTH and a stable source of
signals at several frequencies of interest. I entered each of those in my
receiver's memory, along with one of the (formerly) clear-channel MW
broadcasters from Dallas, a few shortwave broadcasters (whose paths didn't
cross the eclipse track) for reference, the CHU shortwave time signals from
Canada (on the opposite side of the eclipse, but at a later time), and a few
aeronautical beacons from the central states in the 200 - 400 kHz range that
I can normally pick up at night.
I found that I could scan all of these, logging S-meter indications and any
audible effects, in less than three minutes. (This proved to be the source
of considerable writer's cramp once the actual loggings were underway. If I
ever do this again, I will dictate into a tape recorder.) I decided to
perform the scans on a five-minute cycle during the main event, which would
allow me to return to any frequencies of particular interest twice or more
during that time on a case-by-case basis. I began logging at 10-minute
intervals from roughly two hours before totality reached the midpoint of the
WWV/WWVB propagation path, to two hours after, switching to five minute
intervals as soon as it appeared anything was happening.
And indeed it did happen! The 2500 kHz and 5, 10, 15, and 20 Mhz WWV signals
went through an approximation of sunset, night, sunrise, and daytime signal
levels again, all in the space of just over half an hour. The relative
strengths of 15 and 20 Mhz were different for an extended period after the
eclipse, although not having had another eclipse with which to repeat the
experiment makes it impossible to say whether there's any significance to the
observation. Later, the CHU time signals underwent a similar night and day
reversal.
On MW, there was distinct audible enhancement of the Dallas station, but it
didn't move the S-meter into a useful part of the scale. The LW aerobeacons
were even less productive. None of the reference shortwave broadcasters'
signals appeared to be affected.
However, 60 kHz yielded quite dramatic results. Well before and well after
the eclipse, the WWVB signal was at its normal daytime level here, marginally
above noise. Almost 40 minutes before center-path totality, though, it faded
out entirely! It later returned, rising to nighttime levels (over 10 db
above daytime levels) when totality was over the center of the propagation
path. After totality, it again faded to oblivion for a time, finally
returning to daytime levels. This seems to parallel the fade we normally
experience from WWVB here at sunrise and sunset.
My guess would be that the longest, most profound effects will be seen below
about 100 kHz. Above that frequency, effects do occur where the eclipse
track crosses the propagation path; but the higher one goes in frequency, the
less change I'd expect to see in signals not directly crossing the track.
We'll see how it turns out in practice. Good luck to all.
73,
John KD4IDY
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