[TowerTalk] Is it me

Jim Brown jim at audiosystemsgroup.com
Thu Dec 28 18:49:26 EST 2017

On 12/28/2017 3:11 PM, john nistico wrote:
> I have tried modeling a 15/20 duoband antenna. I get 20 to play nicely but can't get 15 to work at all. When I model 10/15 I can get both to work great. Any insight ?

Study parasitic currents in all the elements, taking into account 
terminations. Compare currents (or patterns) with all elements in place 
with what happens if one or more elements isn't there. If elements are 
driven in parallel, take into account that the transmitter, as 
transformed by the length of the line, may have a matched source Z (or 
not badly mismatched) at the operating frequency but a very different Z 
on the other band.

Take this for what it's worth, from a guy who realizes that the 
performance of any passive system depends strongly on source and load Z, 
but who is NOT at all experienced with the design of multi-band 
aluminum. :)

If you want something to study, I'd start with N6BT's "Array of Light," 
which has a LOT of great practical engineering advice on things like 
this. I bought my copy from K7LXC's website. Looks like Tom is selling 
it on his own website.


Dunno if G0KSC has written anything on this, but if he has, I'd study 
that too.

73, Jim K9YC

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