[Top] [All Lists]

[TowerTalk] Shunt Feed Capacitor for Tower

To: <>
Subject: [TowerTalk] Shunt Feed Capacitor for Tower
From: (Tom Rauch)
Date: Sat, 9 Feb 2002 07:44:39 -0500
> I have a large KLM log periodic that I plan to put up at 100 feet. It
> is this tower that I currently use as a top loaded vertical for 160. I
> also had concerned about arcing when I realized the elements of the
> log are insulated from the boom. I called KLM's successor, M2 I
> believe, to ask if this was a problem. The fellow I spoke with said
> that never in his time with KLM or M2 had there ever been a report of
> a problem such as this. He simply did not think it was an issue. And
> remember, he wasn't selling me anything. This is an older antenna that
> I already have on hand. 

The log might be OK, depending on how the balun is configured 
and designed. Or it might not be. The elements would be grounded 
through the balun's common mode impedance.

Most baluns won't have enough impedance to isolate the elements 
on 160, so the biggest worry might be the balun heating or failing 
on 160 or the feedline arcing to the tower leg near the tower top.

I had a small KLM log about 15 years ago, and had a problem with 
the feedline arcing through the jacket to the mast right where the 
feedline was taped to the mast when I operated 160 meters.

Yagis are a different story, because the elements are not tied 
together with a feed system. I received at least two e-mails in the 
last year or so from 160 ops who have had that problem with KLM 
yagis (NOT the logs) on shunt fed towers, and one of them reported 
a friend of his had the same problem. As I recall, all of them 
reported running high power. Small air-wound chokes of #12 or 14 
wire cured all the problems.
73, Tom W8JI 

Where do you get ICE bandpass filters & beverage matching boxes?  The
same place that pays for the hosting of this list:  The eHam Store.
Order online at

FAQ on WWW:     
Administrative requests:

<Prev in Thread] Current Thread [Next in Thread>