Dear Bob,
Great to hear from you, as always. Boy, I wish I had your knowledge/wisdom
in these matters.
I actually forgot to mention one crucial thing - there was no actual peak
of the signals as sunrise approached, ie the signals I could hear seemed to
stay at a similar average level throughout the 25 minute or so period I
operated (taking into account the massive QSB on them) - when I worked
stations from the same areas, they were at the same strength near/on
sunrise as they were 25 minutes before sunrise.
The other factor I have since discovered is that Mike VK6HD, some 450 km to
the SE of me, experienced the usual typical enhancement in signals levels
as sunrise approached. With him the better signals from Eu were peaking
around S9 at sunrise, while they were only S5 with me at maximum. Mike was
also using a similar inverted vee antenna (with the apex around 80 - 90'
above ground).
What a difference a few hundred kilometres on the topband can make.
Vy 73,
Steve, VK6VZ
At 04:12 PM 23/11/1999 -0800, you wrote:
>Steve,
>
>Very interesting post; thanks so much.
>
>As you may know, I think signal ducting is an important mode on Top Band.
>Recently, my friend, VE7DXR, completed a two-year study of dawn
>enhancements on 1.566 MHz (HLAZ in Korea). His data indicate that the
>enhancements peak and signals start to fade when sunligt reaches about 200
>km altitude on the path. My ducting interpretation is that signals are
>dumped out of the duct by ionospheric tilts due to sunrise - and those
>tilts would steepen the radiation angle, as you noted.
>
>I think that part is fairly easy, from the standpoint of magneto-ionic
>theory, but the non-reciprocity is harder and depends on more than just
>one factor, as is the case for dawn enhancements.
>
>I hope to work you in the upcoming contest. Alas, I just "fried" part of
>the loading circit on my vertical so I have some work to do.
>
>73,
>
>Bob, NM7M
>
>
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