[TowerTalk] tower resonances

[Rudy Severns]

Pattern distortion is one consideration Rick, but if you're talking about an 
array things get a lot worse.

In an array, besides the obvious distortion possible from adding another 
element (a parasitic element) you will also alter the self impedances of the 
elements.  Each one probably a little differently.  The result is that the 
feed network will not see the loads its design was predicated on and as you 
try to switch directions the array will no longer be symmetrical.  In 
addition to the extra unintended element you will have incorrect element 
excitation in the driven array.  That will really give you pattern 
distortion.

My thought was that you would want to measure your tower(s) right up front 
before you even made a final decision on a new antenna much less built 
anything.  That way you know what to expect and that might change you 
decisions on location, etc.  A present people tend to put up the new antenna 
and if they notice a problem (they may not even if it's there!) go to the 
nearest tower and put some kind of skirt on it and tune around until you 
reduce the effect.  That can work but I would prefer something a bit better.

As I mentioned earlier, I have a method to make those measurements but it's 
not practical for most hams.  That's why I've been asking if anyone else has 
a less complex solution to this kind of measurement.

73, Rudy N6LF