Topband: Top-band Prop along grayline?

[by way of Bill Tippett <btippett@alum.mit.edu>]

What KT2Q is pointing out is that there is a gap between our assumption
that it is long path based on which way our antennas are pointed and our
understanding of the ionosphere. Our model of the ionosphere is a monthly
median model, and it indicates that there’s way too much absorption on 160m
along or near the terminator for even short path. This suggests one of two
things is happening:

1. Something happens along the terminator with respect to absorption on a
couple days of the month (which our monthly median model doesn’t catch)
that indeed makes it long path.

2. Something else is going on that makes it look like long path.

A good example of ‘something else is going on’ is a 40m QSO that Jim W6YA
had with George JY9QJ at 0412 UTC on October 4, 2003. Jim reported hearing
George best out of the southwest. My first thought was that it was a skewed
path QSO (not long path, as there's too much daylight), as short path from
W6 to JY is to the northeast. But during the QSO Jim had George turn his
Yagi, and interestingly Jim heard George best when George’s antenna was
pointed along the short path from JY to W6. So it looks like it was indeed
short path from JY, it over flew Jim, and then came back in from the
southwest. Without George’s data, I would have erroneously chalked this up
as a skewed path QSO as opposed to really being short path with a mechanism
that brought it back into Jim from the southwest. The mechanism on Jim’s
end that brought it back in from the southwest is likely to have been the
equatorial ionosphere with its steep gradients a couple hours after sunset
during the month of October.

Note that I’m not saying the 160m QSOs to JA weren’t long path. All I’m
saying is we don’t have a match between our assumption and physics from our
monthly median model. Thus something is amiss here.

Carl K9LA