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Re: LF: eclipse

To: [email protected]
Subject: Re: LF: eclipse
From: [email protected]
Date: Fri, 6 Aug 1999 12:34:24 EDT
Reply-to: [email protected]
Sender: <[email protected]>
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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