I've been using YT for years. Recently, I upgraded my terrain profile to
Europe to one with much higher accuracy than before. The profile is
essentially flat within about 50 feet out to 2 miles, but the
higher-resolution plot reveals many small ups and downs of 10-20 feet in
magnitude.
When I ran this terrain plot against my antennas (a tribander stack), I was
tremendously surprised to discover that the resultant elevtion pattern
includes a VERY strong, very low-angle component. Compared to the same
antennas over flat ground, the pattern is approximately 14 dB better at 1.5
degrees elevation on 21 MHz. The enhancement at that same angle is
approximately 12 dB at 28 MHz, and at 14 MHz, the enhancement at 1.75
degrees is approximately 17 dB. On 7 MHz, with a single yagi at 104 feet,
the 1.75 degree enhancement is right off the chart, at over 20 dB.
Just for fun, I ran the same antennas in TA, with the same terrain profile,
and the results are at least qualitatively identical. Of course, I have no
way of knowing whether both programs use the same or similar
reflection/diffraction methodology.
I would welcome advice on whether what I'm seeing here is
real, or just a modeling artifact. It's been suggested that my washboard
terrain might be acting to enhance signals at very low takeoff angles, in
the way that I gather a diffraction grating can scatter light arriving
almost parallel to the plane of the grating. Anyone out there with a
physics or optics background care to comment?
By the way, before anyone asks, I really can't judge from practical
results. On most bands, the percentage of signal arriving at these angles
is very low, and I haven't had sufficient experience with high-performance
antennas to give me much of a baseline.
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