Hi Kelly:
I think you will be okay using a coax balun...that is what I use on both
my 80 and 40m Yagis now....I still have a relay at the driven elements
of both beams since I want the baluns to be "transparent" for the 160m
loading, but you probably won't need it. Without a relay, the tower may
"see" a little less toploading. See here if interested for a photo of
my coax Baluns: http://www.qsl.net/ve6wz/mechanical.htm
Steve ve6wz.
> -----Original Message-----
> From: Kelly Jones [mailto:kjones@virtualcohesion.com]
> Sent: Monday, June 12, 2006 7:50 PM
> To: VE6WZ_Steve; TowerTalk@contesting.com
> Subject: RE: [TowerTalk] Cushcraft XM240 & Shunt fed tower
>
>
> Steve,
>
> Thanks for the great information. I wonder if heating will
> be an issue with a coax balun? I did have the MFJ BN76 (or
> whatever the model # is) balun on the antenna up until about
> a month ago. At that time I took it down and tore everything
> apart looking for an intermittent. When I put it back on the
> tower I replaced the "boxed" balun with a coax one (I've
> become a fan of coax baluns). Would there still be heating
> in a coax balun?
>
> 73
> Kelly - N0VD
>
> PS - sorry for the "double" post. I think my first message
> got held for approval since I inadvertently sent from a
> non-subscribed address. It must have recently been released
> by the moderator.
>
>
>
> -----Original Message-----
> From: VE6WZ_Steve [mailto:ve6wz@shaw.ca]
> Sent: Monday, June 12, 2006 5:35 PM
> To: Kelly Jones; TowerTalk@contesting.com
> Subject: RE: [TowerTalk] Cushcraft XM240 & Shunt fed tower
>
> Kelly:
>
> Don't forget about the driven element.
> That driven element may have a DC ground through the coax
> shield, but the current balun can get real hot carrying the 160m RF !!
>
> A WORD OF CAUTION when shunt feeding a tower with an XM-240
> on top: There is a very good chance you will "cook" the balun
> unless you short the driven element to the boom when TX on
> 160m. Here is a photo of what my XM-240 CC balun looked like
> after a year of shuntfeeding the tower on 160 without
> shorting the current balun:
> http://www.qsl.net/ve6wz/CCbalun.htm > I came to suspect this
> problem when I could see the 160m SWR slowly drift with KW
> key down as the balun heated up !!!
>
> It's likely each shunt-fed tower setup may act differently
> depending on the top loading configuration (other Yagis etc.)
> but you may want to put a small relay at the driver. I just
> use a small 12v relay that is powered in parallel with my
> tower mounted switch box.
>
> BTW...before I grounded my XM-240 reflector I would here the
> same "tick"-"tick" sound, but not only when electrical
> activity was nearby, but also on warm breezy sunny days too.
> Wind static ???
>
> de steve ve6wz http://www.qsl.net/ve6wz/
>
>
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