On 9/20/2017 10:35 PM, Stan Stockton wrote:
I am curious. The coax/tower (we'll call it Antenna 1) is isolated from
Antenna 2 (the real antenna) with a choke.
Antenna 1 is still radiating the noise without, let's say, direct connection to
Antenna 2.
So there is no propagation such that Antenna 2 picks up the noise radiated from
Antenna 1, end of which is at most a few inches away?
Good question. The answer is, yes, and it's a question of degree. Let's
assume that Ant 2 is a horizontal beam. This makes it cross-polarized
with Ant 1, so there's much less coupling than if they were not
cross-polarized. Also, the peaks of their radiation patterns are the
direction of the other antenna. The result is that it's a LOT less
coupling than direct via the common mode current.
Feedline chokes don't usually provide a LOT of noise reduction unless
what you're starting with is a train wreck, but neither do Beverages. If
you're trying to work the weak ones, 3-6 dB better signal to noise can
make a big difference! As N6BT wrote in his self-published "Array of
Light" book about antenna design, that level of improvement gives you
another level of stations to work!
73, Jim K9YC
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