Date: Mon, 26 Jul 2010 06:21:30 -0400
From: Pete Smith <n4zr@contesting.com>
Subject: [TowerTalk] Gas Tube protection for remote antenna switches;
shorting coax cables when disconnected
Yesterday we had a severe thunderstorm episode, with significant
cloud-to-ground lightning nearby. All my coax and control lines were
disconnected, but when one particularly close strike occurred, an arc
jumped across the open SO-239 on my entry panel. No damage in the
shack, fortunately, but it set me wondering.
1. Does it make sense to put a shorting plug at the shack end of a coax
cable? With my Ameritron RCS-10 relay box, putting a shorted PL-259 in
position 1 on the relay box has the same effect when the control cable
is disconnected, except at the tower end. A better idea?
## putting a shorted pl-259 in pos #1 just used up pos #1.
Why not use a torroid.. like 45 uh... using 10-12 ga magnet wire. Then,
the center conductor is always at DC grnd. [ on the cable heading towards
the station.. ie: input side]
## does the ameritron grnd, or float the un-used ports ?? My AS
box grnds all the unused ant ports. DPDT relays are used, one per
port. Common goes to ant port, NC goes to grnd buss... and NO
goes to kw input buss. If lightning present, all Unused ports are grnded.
If power to control box is shut off, or rotary switch thrown to pos 7-12.. then
all ports 1-6 are grnded.
## You could also install an ICE arrestor, or similar, at shack end... then
the center conductor is always DC grnded...plus it has a gas discharge tube
in parallel with the 12 ga , 35 uh torroid they use. It's also dc blocked...
and
the station side of the block caps has series resistors going to grnd. You
could
also install a 2nd torroid on the station side of any dc block cap.
## I'd also grnd all the braids if all coax cables at the top of the
tower....
then run the coax down the inside of the tower .. and also grnd the braids at
base of
tower. Then install the ICE arrestor or eq in the station.
## IF the yagi uses either a hair pin [floating] or a beta match [ grnded
hair pin] then the
center conductor is grnded anyway. If no hair pin is used... like on an OWA
design.... I see no reason
why a 35-70uh choke couldn't still be used directly across the DE. If a
remote switch box is used, at least you have
all the braids grnded at top of tower already.
2. Ameritron makes a "lightning-protected" version of the RCS-10,
called the RCS-10L. From the parts list (no schematic) it appears that
the only added component is a gas tube, rated at 1500V, 10 KA. I
presume this is across the output of the relay box coming to the shack.
Again, good idea?
## sure, that will work. But can u take the box apart to change out the
gas discharge tube, with no hassle ? On the German Hoffi brand lightning
arrestor's, it takes no time at all to change out the gas discharge tube.
Same
deal with the Suhner + also the Spinner brand of lightning arrestor's.
## did Ameritron install the gas tube on the side of the remote box... for easy
access ?
1500 V means the gas tube is good for 20 kw with flat swr... and 10 kw
with a 3:1 swr.
Later... Jim VE7RF
--
73, Pete N4ZR
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