OK, guys ... I had no idea when I mentioned a pair of Force 12 antennas as
examples of potential shadowing that this would evolve into a wrangle over
those particular antennas. Let's try to get general again.
Just for fun, I modeled a simple test case. I took the 3-el NBS yagi model
that ships with EZNEC, and scaled it to 7 and 28 MHz. The free space gains
and patterns were substantially identical (to a couple of hundredths of a
dB) to those of the reference antenna (at 50.1 MHz), which I took to mean
that the scaling was substantially OK.
Next, I modeled the 10-meter yagi at 50 feet above an average MiniNEC
ground. It showed 14.99 dBi gain and 9 dB F/B ratio.
Then I added the 40-meter yagi to the model above the 10-meter yagi at
various heights, with the following results:
40/10 hts (ft) 10m gain 10m F/B
--------- --------- -------
80/50 15.46 dBi 9.5 dB
70/50 15.28 dBi 10 dB
60/50 14.03 dBi 9 dB
I'll leave the interpretation to you, except to note that according to
NEC-2, the 10-meter antenna is clearly "seeing" the 40-meter antenna above
it as far as 30 feet away.
73, Pete N4ZR
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