Topband: Inverted L SWR Jumps ???

[Jim Brown]

On 11/27/2012 10:45 PM, Tim Duffy K3LR wrote:
> There is significant coupling between 160 meter antennas that are separated by as much as 500 feet

YES!

> and this coupling could be problem for your set up.

But it can also be a good thing if you know what you have and how to 
take advantage of it.  I have three resonant verticals for 160M, as well 
as a tower that is resonant on 160M. Studying them in NEC early this 
summer, I've learned how I can drive each of them, one at a time, and 
use the others as passive reflectors to get 4-5 dB of gain in several 
directions.  The patterns that NEC predicts are clearly observable on 
the air.

It doesn't take much to couple and change an antenna's pattern. I first 
saw this when I had hung a new dipole near an 80M vertical, and that 
feedline coupled to the vertical.  I choked the feedline and the 
coupling went away.  N6LF published something quite useful on this topic 
several years ago showing that even a fairly short tower that is well 
below resonance, even loaded with aluminum on top, can significantly 
affect a pattern. I have one such tower that NEC predicts will resonate 
around 2.3 MHz, and a bump of a few dB. Taming that (probably by 
detuning it) is something else I need to work on. N6LF's piece is on his 
website.

73, Jim K9YC