Date: Tue, 23 Jul 2013 16:05:13 +0200
From: "Peter Voelpel" <dj7ww@t-online.de>
To: <towertalk@contesting.com>
Subject: Re: [TowerTalk] Which Balun with the TH7DXX
Yes, I am pretty confident that it works on 20m.
30uH give me 2638 ohms.
On the feed line I measure no common mode current either.
I am using such on a 20m KLM yagi now which I converted to OWA two weeks
ago.
I use the same kind of choke on my 7 element 10m OWA but with 20 windings on
a 4" pipe.
It will be used on a new 6 element 15m OWA which I am just working on.
And next year I will convert 4 more KLM yagis and use this kind of balun
with them.
All coax cables are earthed to the boom after leaving the chokes and to the
top of the tower, half way up and at the bottom of the tower.
The tower is fed as a vertical on 160m and so far no problem with arcing or
band to band interference.
73
Peter
## using XL = 2 pi * FL, 30 uh = 2637.8 ohms @ 14.0 mhz. But it’s all
inductive.
Then you have to factor in the C between turns. The assy will be parallel
resonant at some freq,
hopefully 20m band...then the Z will be sky high. Below the parallel resonant
freq, it will look inductive.
Above the parallel resonant freq, it will look capacitive.
## IF the braid was grounded to the tower 1/4 or 3/4 wavelengths away from
the balun, the XL of the
balun could be cancelled out by the length of the feedline between balun and
where its grounded to the tower.
## Bottom line is... if you don’t see any or very much shield current down
stream, using a clamp on RF ammeter,
the system works.
Jim VE7RF
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