Date: Wed, 6 Jul 2016 18:25:05 -0400
From: "James Wolf" <jbwolf@comcast.net>
To: "'Kim Elmore'" <cw_de_n5op@sbcglobal.net>,
<towertalk@contesting.com>
Subject: [TowerTalk] Log Periodic Feed
Continuing the discussion on how to attach the coax to the ?hot? boom of a
Tennadyne T8 antenna.
As I assembled this antenna, I became increasingly confused and concerned about
the feed system. With this log antenna, instead of running open feedline
wires crossing over to the elements, it uses two boom pieces and each is
insulated from the mast and each boom is ?hot?. The instructions indicate and
show how to attach the feedline to the bottom boom piece using a Collins type
balun at the feed point which is at the forward end of the antenna.
My concern is that of the coax shield separated only by the coax insulation
alongside one of the ?hot? boom pieces would couple and cause radiation (phase
shift) problems with the antenna or at the very least radiate as it goes
vertical down the mast.
Due to the element mounting method it is not possible to run the feedline
inside the boom to the mast.
Does anyone have any thoughts on why running the coax along the ?hot? boom
would be an OK idea?
And if not, how else would one feed the antenna?
Jim ? KR9U
## http://w8ji.com/baluns_on_log_perodic_antennas.htm I forget how a
collins balun is constructed, but if its just a 1:1 balun, you may be better
off using a quality CMC device at the feedpoint. Then another CMC on the
coax..where it leaves the boom.... and then forms the rotor loop. If coax
taped to hot boom, it will induce RF into the braid....hence the CMC .. right
where the coax leaves the boom..and forms the rotor loop /splice ..and heads
down the tower.
Jim VE7RF
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