[TowerTalk] Detuning booms?

john at kk9a.com john at kk9a.com
Sun Oct 19 21:39:01 EDT 2008

I'm assuming that the 40m elements are insulated or the boom would be much 
longer than 1/2 wl on 20m.   You could ground the elements, but you would 
have to manipulate the antenna a little to do so.  You didn't say how far 
apart the antennas are, but it sounds like your TIC ring is very near the 
top of the tower.   Assuming that this is the case, you could connect an arm 
from the TIC ring to the mast, replace the mast rotator with a lower bearing 
and turn everything together using the TIC, unless you need the ability to 
beam one direction on 20m and a different direction on 40m    Or your could 
mount the 40m beam to your mast and use the TIC further down the tower for 
something else.

John KK9A

Subject: Re: [TowerTalk] Detuning booms?
From: Michael Dinkelman
Date: Sat, 18 Oct 2008 21:40:44 -0700

Hi Steve

I have 2 yagi's, a C31XR and a 3el 40M (old KLM) I just
refurbished and put up underneath it. As long as the two
booms are lined up. All is fine. (At least that makes it simple :>)
If they start pointing in different directions, the
20M SWR starts rising.

The 40M antenna's boom is about 30+'. I figure it's close
enough to 1/2 wave on 20M to make a difference. I might be
able to raise the C31XR a couple more feet on the mast - there
is about 8' between them now. I expect we'll try that first but
I don't expect it to make a difference.  The 40M is on a
Tic Ring and isn't going anywhere for now (it took 3 months
to align the moon and the stars enough to get it on the tower :>).
So that'll make  it hard to hang wires off the end.  :>)

At least I have a work around for now - keep 'em lined up while
I'm on 20M. :>) 

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