Fwd: [TowerTalk] A4S SWR correction-new problem

TexasRF@aol.com TexasRF@aol.com
Sun, 15 Feb 1998 09:30:20 EST

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From: TexasRF@aol.com
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To: kb3aug@juno.com
Subject: Re: [TowerTalk] A4S SWR correction-new problem
Date: Sun, 15 Feb 1998 09:29:32 EST
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The half sloper antenna is *very* sensitive to whats on the top of the tower.
Essentially the tower is the radiator and all antennas add top capacitance
loading. It is possible that the old balun was acting as an rf choke between
the A4 driven element and the shield of the coax feeded the A4 (actually that
is the purpose of a balun), effectively isolating the driven element from the

The new balun perhaps has less inductance and less rf isolation (we are
talking about 75 meters here, not 20m) and is allowing the driven element to
become a significant added top load.

The rest of the path for rf would be the capacitance between the A4 coax
shield and the tower since the coax is probably taped tightly to a tower leg.

If this is indeed the case, then there is going to be a bunch of 75m rf
accross the balun  and could easily fry a wimpy balun made of small wire
inside. Also, if this is the case, the old ferite core over the coax trick
should improve the situation.

How's that for a wild guess?

73 de Gerald, K5GW


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