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[TowerTalk] Static discharge Cushcraft XM240 during storms

Subject: [TowerTalk] Static discharge Cushcraft XM240 during storms
From: <>
Date: Thu, 25 Aug 2005 15:15:55 -0500
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I have experienced exactly the same thing with my XM-240 here in Iowa.  I
could hear the static jump during winds and passing storms.  Here are a
couple of other observations:

1)  I use an Ameritron Coax Switch and the feedline is grounded.  What you
are hearing is the reflector arcing to the boom across the small insulator
rings in the U-bolts.

2)  I modified my XM-240 after having two of the loading elements blow up
in near lightning hits.  (And I mean blow up.  I have aluminum spatter and
the wire was tangled.  The heat shrink tubing was blown away.  And that was
from a near hit.  Happened twice in two consecutive summers.)  Here's how I
modified it.  I grounded the reflector to the boom and I added two of the
Wireman's "porcupine" static discharge devices on top of the tower where
the phillystran relief cable attaches to the mast.

A bit of history is in order.  The XM-240 was both a structural and
electrical improvement of the original 40-2CD.  The electrical change was
to insulate the reflector to improve the pattern.  Apparently there was
some imbalance and by insulating the reflector it cleaned up the pattern.
But the capacity hats with their nice pointy ends form nice discharge paths
for static build-up.  So when a storm passes or there is precipitation
static they fire form the ends of the capacity hat.  I just put the
porcupines up to help provide an alternate path for the discharge.

Seems to work.  Haven't had a problem in three years since the change.

For reference my XM-240 is at 82 feet above a Cushcraft X-9 on top of a
Trylon self supporting 72 foot tower.

Hope this helps.

Rick N0YY


See:  for "Self Supporting Towers", "Wireless Weather 
Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions 
and ask for Sherman, W2FLA.

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