[TowerTalk] Cushcraft XM240 & Shunt fed tower

Keith Dutson kdutson at sbcglobal.net
Mon Jun 12 13:41:26 EDT 2006

I heard stainless is not good for carrying RF current.

73, Keith NM5G

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Pat Chiles
Sent: Monday, June 12, 2006 12:08 PM
To: Kelly Jones
Cc: towertalk at contesting.com
Subject: Re: [TowerTalk] Cushcraft XM240 & Shunt fed tower


I shorted the reflector of my XM240 when I initially installed it.  This was
after I noticed no difference between shorted and unshorted. 
Characteristics seem to be very close to what CC publishes.

I shorted the reflector by using a stainless steel hose clamp around the
middle and then screwed the hose clamps "tail" to the boom.

Pat, K8PC
----- Original Message -----
From: "Kelly Jones" <kjones at virtualcohesion.com>
To: <TowerTalk at contesting.com>
Sent: Monday, June 12, 2006 11:46 AM
Subject: [TowerTalk] Cushcraft XM240 & Shunt fed tower

> Hello TTs,
> As some of you may recall, I'm in the process of shunt feeding my shorty
> tower for 80/160.  On top of this tower is a Cushcraft XM240.  Some have
> suggested that I may need to ground the reflector in order to get enough 
> top
> hat loading.   Some have also suggested this in order to prevent arcing at
> high power from the boom to element as well.
> Well, I had an interesting event take place yesterday afternoon.  We had
> what was essentially a "dry" thunderstorm come through.  The air was very
> "charged".  You could just feel it.  I happened to be in the back yard and

> I
> kept hearing this "tick, tick, tick" noise.  After a little investigation,
> this noise appeared to be emanating from the back of the XM240.  Then I
> happened to notice that every time there was a cloud-to-cloud lightning
> strike, the "tick" would become a "crackling" noise.  The intensity of the
> "crackle" would depend on how close the lightning strike was.  On a couple
> of occasions, I noticed the area around the rear of the XM240 light up 
> with
> white light when it would "crackle".  This caused an extremely uneasy
> feeling!
> I was not brave (or dumb enough) to walk out underneath the antenna to see
> if I could visually see where it was arcing, but my gut tells me it was
> between the reflector and boom.  So my question is has anyone put a ground
> strap between the reflector and boom?  Would this change the 
> characteristics
> of the antenna?  I tried contacting CC to bounce the idea off of them, but
> trying to get to a real person doesn't seem possible.  I know that the 
> older
> 402CD did use a ground strap but for whatever reason the XM240 does not do
> this.
> I am pretty certain this will change the my shunt feed project as well,
> hopefully for the better, but I obviously have an issue that needs
> addressed.  I suspect if I do nothing it's just a matter of time before 
> the
> smell of ozone is in the air (and in my shack).
> 73
> Kelly - N0VD
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