David,
Arrange for your local friends to be on the air during
the daytime (around local noon). At the time, you can
be pretty much assured that absorption will be so high
(at least at the current solar flux) that if you are hearing
them at all, it is via ground wave.
What I suspect you will find, is that you'll hear them
better at local noon on the vertical low-angle antenna,
but the signal will be down from the nighttime peak.
The other giveaway is to look for fading at night. If
you see fading then you can be pretty certain that
skywave (or some combination of skywave and
groundwave) is involved. I work local friends on 75
meters that are within 10 to 20 miles. Signals at
night are anywhere from S5 to 40 over S9 (when
80 goes long they get really weak), suggesting that
the path is dominated by NVIS propagation.
If your hearing the local guy better on a horizontal
antenna you can almost guarantee that it's via NVIS
and not groundwave.
73 de Mike, W4EF............................................
----- Original Message -----
From: "D. Rodman, MD" <rodman@buffalo.edu>
To: <topband@contesting.com>
Sent: Thursday, October 14, 2004 11:50 AM
Subject: Topband: Angle of radiation to local stations?
> I did some on air testing with some bidirectional antennas for 160m and
> the results were somewhat surprising to me. It appeared the antenna which
> should have favored the direction of the local stations was an S unit
> lower. The antenna is a low angle radiator with vertical polarization.
> When I checked the modeling of the antenna, I see the low angles favor one
> direction for DX but the higher angle signals are several dB stronger in
> the opposite direction. This leads me to think about what angles 160m
> stations within 15 miles might be copying best. If this is high angle, my
> observations are explained. I am confident the ground wave propagates
> based on field strength for a while but I am not sure what distance
> skywave at higher angles begins to seriously affect on this band. I am
> most familiar with the upper bands. Thanks.
>
> David J. Rodman, MD
>
> Assistant Clinical Professor
> Department of Ophthalmology
>
> Research Assistant Professor
> Department of Chemistry
>
> State University of New York at Buffalo
>
> FAX 716-859-4565
> Office 716-854-1137
>
> e-mail: rodman@acsu.buffalo.edu
>
> _______________________________________________
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>
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