Hence why I feel a helluva lot better with a good olde fashioned roll of
wound up coax, my 3 stack on 20 uses that and am probably going that route
on 40 meters next....we have had one 40-2CD up in the air for almost a
decade now with a wound up coax balun - still making QSOs faithfully!
K4OJ
----- Original Message -----
From: "VE6WZ" <ve6wz@shaw.ca>
To: <towertalk@contesting.com>
Sent: Tuesday, June 11, 2002 4:48 PM
Subject: [Towertalk] Cushcraft melted Balun
> 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
the
> outer jacket on the Teflon coax has cracked in numerous places. I have
> posted a few pictures here: http://www.qsl.net/ve6wz/CCbalun.htm
>
> 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,
and
> the yagi wants to be part of the action on 160 : )).
> I recall a post recently about the need to ground insulated yagi elements
on
> shunt fed towers......maybe this is another reason. My tower loaded fine
on
> 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
tower.
>
> de steve VE6WZ.
>
>
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