I didn't follow your discussion that well but; You should NOT ground the coax
shield anywhere between the antenna and the choke, that will defeat the purpose
of the choke.
It's a very good idea to ground the shields of all your coax feeders before
they descend down the tower, that way the current from a lightning strike is
somewhat deflected away from your shack.
Using a metal box to contain your current choke is OK as long as the shield of
the coax between the antenna and the choke is not connected to the box, e.g.
you should use connector isolated from the box.
If you connect both sides of the choke to ground you short out the choking
function.
Best 73 de,
Hans - N2JFS
-----Original Message-----
From: Jim Thomson <jim.thom@telus.net>
To: towertalk <towertalk@contesting.com>
Sent: Sat, Nov 1, 2014 7:52 am
Subject: [TowerTalk] Terminate braid at top of tower...or not?
Is it better to ground the braid of the coax coming from a yagi.... to the top
of the tower, or not? I will be using a remote switch box at top of the
crank up tower, as
I don’t want to use more than one coax going up the side of the motorized
tower.....to save weight. I could use the metal box....and ground all the
braids of the coaxs
form the yagis to top of tower. I can also use a waterproof plastic nema
box....and float all the braids from the top of tower. IF I use a plastic
nema
box for the remote
switch box, I can install a single choke balun on the input of the remote
switch
box..... to supplement the individual choke balun at the feedpoint of each
yagi. The thought
here was, if a metal box is used..and residual RF that gets past the yagi
balun...will then flow down the tower legs..rendering any balun at input to
remote switch box useless.
Another plan was to install a rf choke balun on the output of each port on the
remote switch box, is a metal box was used. Again these baluns would supplement
the yagi baluns.
At the base of the crank up tower, the hofi lightning arrestor will be
installed, aprx 4 feet up one tower leg..and bonded to tower. It will also
serve as an interface between the
larger LMR-1200DB rigid coax from shack to lightning protection box...and the
smaller RG-393 running up the side of the crankup tower. IE: braids of both
coaxs will be bonded to
base of tower. Each tower leg gets a 2 ga stranded, bare cu wire going to
its own individual 8 ft ground rod...and cadwelded at ground rod. Top of
each rod is aprx 5 inchs below
ground level, buried below the lawn, on the perimeter of the concrete base.
Shack end of LMR-1200 has its braid bonded to a SPG on basement wall. I also
ran 2 ga cu wire from base of tower to a 4th ground rod outside basement. Then
more 2 ga cu from
4th rod to SPG plate..aprx 4 ft. 4th rod is cadwelded too.
Main issue is whether to bond coax braids to top of tower..or not. Or does
it
make any difference since braid of 393 going up the tower is bonded to base of
tower anyway.
All the braids of all the yagis will be bonded to the braid of the 3093
running down the tower.
Any comments on the proposed plan ?
Jim VE7RF
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