[TowerTalk] Cushcraft XM240 & Shunt fed tower

[VE6WZ_Steve]

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 at virtualcohesion.com] 
> Sent: Monday, June 12, 2006 7:50 PM
> To: VE6WZ_Steve; TowerTalk at 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 at shaw.ca] 
> Sent: Monday, June 12, 2006 5:35 PM
> To: Kelly Jones; TowerTalk at 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/
> 
>