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[Towertalk] Tri-band beams - trap questions

To: <>
Subject: [Towertalk] Tri-band beams - trap questions
From: (
Date: Sun, 1 Sep 2002 08:51:45 -0600
A  TRAP is a TUNED CIRCUIT consisting of a coil and a capacitor.

The ATB34 used a coil and a capacitor consisting of a short piece 
of coaxial cable, using the cable capacitance to tune the coil.

Modern Traps use the capacitance between an inner piece of
element tubing and the outer trap cover to tune the coil.


You can't just replace an ATB34 coil / capacitor with any
modern trap and assume the element will be tuned for 
some desired level of performance.  You MAY be able to
use the element material and a trap designed for the A4
along with the A4 dimensions.

Tom  N4KG

On Sun, 01 Sep 2002 08:10:32 -0400 John Silberman <>
> I have two questions for the group. If I'm wrong, please correct me.
> 1.    Some older tribanders had traps that have a sort of fiber trap
> cover, that is unavailable now.  Because its fiber and not aluminum 
> like
> the modern traps, the cover is not electrically part of the trap and 
> any
> non-conducting material can be used to make a trap cover for
> weatherproofing?  Unlike the late beams that have aluminum trap 
> covers
> which are electrically part of the trap and have to be replaced with 
> the
> same thing.  The antenna in question is an old Cushcraft ATB-34, the
> forerunner to the A4S.
> 2.    Since the trap is just that, and not a loading coil, one 
> should be
> able to replace the old style trap with a new style trap, and
> vice-versa, as long as they are replace in pairs on that element?  
> One
> may have to adjust the spacing between the 10 and 15m traps if they 
> do
> act as loading coils on the higher frequency?
> Thanks!
> John
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