[Towertalk] TH11 SWR Problem

[Jim Smith]

... taped the trap ends.  Hmmm.......  

Phil Duff na4m@texas.net <mailto:na4m%40texas.net>
Mon, 31 Aug 1998 14:46:59 -0000

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------------------------------------------------------------------------

Brian wrote:
->TH6DXX trap end caps rapidly breakdown with UV sunlight, because they
>are manufactured of that horrible substance known as plastic.
>
>Anybody tried any solutions of coatings / tapes on top of the plastic
>that give a LONG LASTING SOLUTION to this problem.
>
>I would appreciate to hear from those that have experienced this
problem
>and have found the perfect answer !!?
>
>Thanks       VK4ATQ       Brian Pittman


For years I have wrapped my TH6/TH7 trap caps with electrical tape in an
effort to
reduce the UV damage to the plastic.  Seemed effective in that respect.

However, Roger Cox from Telex/HyGain recently posted a message that
wrapping
 the trap caps with tape messes up the Q & resonant freq of the trap.
His note below:
------------------
o NOT use tape to protect the trap caps from UV!  I have tried this and
it
severely detunes the trap resonant frequency and Q if black tape is
applied
to the outboard trap cap (high impedance end).  It is OK to place tape
over
the cap on the shorted end (low impedance).  The colorant used in the
trap
caps is specified very closely - too little and there are clear areas in
the plastic, too much and the resonance and Q goes to hell.  It is
probably
better to completely remove the outboard trap cap than to place lossy
black
electrical tape over it!

73 Roger WB0DGF
Telex Communications, Inc.
-----------

Oh well....  maybe letting them rot away is ok.  The traps have drain
holes
and I wonder if the trap end caps are really a necessity when you look
at
the trap construction.  The trap is nothing more than a coil with the
trap
cover as the capacitor.

73 de Phil NA4M




 

Tod-Idaho wrote:

>Fred:
>
>I have been seeing some SWR variation from previous SWR measurements made on
>my TH7DX with a GenRad 1606A RF bridge. The before and after stems from the
>event of installing a Cushcraft 40-2CD about 8-10 feet above the TH7DX.
>Prior to the installation of the 40-2CD I had the TH7 down on the ground (
>actually about three feet above the ground) and realigned the elements
>relative to the boom. At the same time taped the end caps of the traps to
>protect them from the actinic stress of the sun here at 5000 feet above mean
>sea level. Although I don't think I taped over the drain holes, after six
>months I can't be absolutely , positively sure I did not do that. Normally,
>here in the high desert of Idaho, one does not worry about water in traps.
>(About 7 inches of precipitation per year, mostly snow). <<Currently we have
>12 inches of snow delivered just yesterday >>.
>ne.
>