Kelly,
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@virtualcohesion.com>
To: <TowerTalk@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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