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[TowerTalk] Force-12 balun construction

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Subject: [TowerTalk] Force-12 balun construction
From: (Ken Hirschberg)
Date: Mon, 08 Nov 1999 09:14:26 -0700
Greetings, Towertalkians -

There has been some question on the reflector about the construction /
repairability of the Force-12 B1 balun.  As some of you may know,
CAL-AV LABS. is the OEM supplier of this balun.

It is made as follows:  After assembly, the balun is potted with
resin, which is mechanically similar to epoxy resin. The balun is then
placed into a vacuum chamber to eliminate any voids of trapped air, then
cured in an oven.  This encapsulates the entire balun, including
and renders the balun unrepairable as a practical matter, because the
is quite hard.   A cap is added for mechanical support and appearance.
The approximatly quarter-inch gap inside this cap is filled with GE
Silicone II, a "50-year" flexible RTV.  This RTV is for the purpose of
preventing any water from accumulating between the leads.  The RTV does
a small amout of acetic acid during cure, however, it does not come into
contact with the conductors, but only the insulation, which it adheres

I have communicated with Richard Thorne, who had the original question
repairability.  His problem with the open leads turned out to be
mechanical; a length of unsupported coaxial cable had been pulling on
the balun.  He suspects that is what broke the leads, one on the
one on the inside.

Of the thousands of these baluns in use worldwide, they have proven to
fairly "bulletproof".

Regards to all,

Ken Hirschberg, K6HPX,
President, CAL-AV LABS, Inc.

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