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[Towertalk] Cushcraft melted Balun

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Subject: [Towertalk] Cushcraft melted Balun
From: (David L. Thompson)
Date: Tue, 11 Jun 2002 20:02:57 -0400

I use the old collins balun made from 10 loops of coax on my older 402CD.
Maybe going this route might help.   I do remember K5UR's story of the flare
on his tower when operating the 160 Contest
which was caused by overheating the lubricant in the rotor.  So loading the
tower can cause problems.

Pass along some of that rare SSB Dx I hear you working on occassion between
7050 and 7100.

73 Dave K4JRB

> The Balun on my XM-240, 2 el 40m Yagi has been severely overheating.  This
> is the Cushcraft MNXM 1:1 balun which is a stack of three, 1.5" torroids
> wound with about 6 turns of teflon coax.  The plastic box has melted and
> outer jacket on the Teflon coax has cracked in numerous places. I have
> posted a few pictures here:
> I can't imagine that this heating is from 40m current on the shield.
> My conclusion is that shunt feeding the tower on 160m has caused the
> problem.  The XM-240 split driver is insulated from the boom of coarse,
> the yagi wants to be part of the action on 160 : )).
> I recall a post recently about the need to ground insulated yagi elements
> shunt fed towers......maybe this is another reason.  My tower loaded fine
> 160, so I assumed there was sufficient capacitive coupling to the 40m
> yagi......I wonder how many 160m QSO's I've missed because of heating up
> that balun  ; )
> A new 4" air core balun will replace the CC unit.
> Maybe something for others to check this summer while you are up the
> de steve VE6WZ.
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