Date: Wed, 29 Mar 2017 06:24:37 -0400
From: "john@kk9a.com" <john@kk9a.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Breaking boom resonance
## What IF his 34 ft boom is trussed with steel wire ? That would
change the resonance. Story I got was you want to avoid floating half
wave booms, or grounded quarter wave booms. IF the 34 ft boom is
no doubt bonded to the tower, then you end up with 2 x quarter wave long,
grounded
booms, back to back.....= bad news. By adding the overhead wire truss to
support the
34 ft boom, the resonance should change. You could also put an insulator
between truss and mast,
then wire a variable cap across the insulator, to change the boom
resonance..but that would require the
use of 2 x insulators and 2 x variable caps.
## as john noted below, you can also end up with more issues when the ants can
be independently
rotated. On a side note, looking at the f12 book, they depicted a case with a
2 el 80m loaded yagi
mounted above a F12 620-340. The 80m yagi would resonate on 20m. This is
with both yagis
pointed in the same direction, mounted on the same mast. Their fix was to use
vac relays on each 80m ele,
to open off the center, when using 20m.
Jim VE7RF
I had a similar issue with my 20m boom being resonant on 40m. In my case I
made it so the antennas could not be turned separately.
For for a fixed wire beam I think that the easiest solution would be to
use a fiberglass boom.
John KK9A
To: towertalk@contesting.com
Subject: [TowerTalk] Breaking boom resonance
From: Steve London <n2icarrl@gmail.com>
Reply-to: n2ic@arrl.net
Date: Tue, 28 Mar 2017 09:57:35 -0600
I have a 34 foot boom supporting an 80 meter wire beam. The elements of
the wire beam are completely insulated from the boom. 30 feet below that
boom is a 20 meter beam. Yes, there is definitely interaction.
I am looking at techniques for detuning the boom using the W8JI tower
detuning method. Anyone want to make a guess at how long the detuning
section should be, and what value of capacitor would get me in the
ballpark for resonance at 14 MHz ?
73,
Steve, N2IC
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