jim Jarvis wrote:
> Bottom post... see below:
> If we make a vertical resonant on our operating frequency, it is, de-
> facto, non-resonant at the broadcast freq.
> i.e. decoupled. And we shouldn't have to worry.
>
I think a dicier matter might be the ham with the tower supporting a
Yagi that inadvertently winds up being resonant. (hey, makes Rudy's
recent questions a lot more relevant).
"
(b) Construction near a directional AM station. Proponents of
the construction or significant modification of a tower which is
within the lesser of 10 wavelengths or 3 kilometers of the AM
station, and is taller than 36 electrical degrees at the AM
frequency,
"
36 degrees at 1500 kHz (lambda 200m) is only 20 meters (66 ft).. lots of
towers in that height area, and a shorter tower with a yagi on top could
easily have an electrical length of 20m. Or, a not sufficiently
decoupled feedline could wind up being a problem. I would think that 36
degree electrical height (1/10th wavelength) would be pretty far from
resonant, and a chore to measure.
I suppose the real issue is whether the ham's antenna does "bad things"
to the DA pattern of the broadcast station, i.e. fill in a null. I
can't see a non-resonant (lambda/10) element 10 wavelengths away making
a huge difference in main lobe levels, but I could easily see it causing
a problem with a 20dB null, if such are ever required.
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