[TowerTalk] 40M rotary dipole

[Jim Brown]

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