[TowerTalk] Cushcraft XM240 & Shunt fed tower

Kelly Jones kjones at virtualcohesion.com
Mon Jun 12 11:46:24 EDT 2006

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
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
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).
Kelly - N0VD

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