Jim,
For lightning, you want to ground the shield both at the top of the tower
and the bottom. If the tower is taller than say 100' then another ground
1/2 way down. This keeps the tower and the feedline at the same potential
from the top to the ground if/when it takes a strike. If not, the tower can
arc over to the feedline and destroy it.
Your grounding at the bottom also is a "colder" point than the top, so you
will definitely want to keep that.
You want to put any balun as close to the feedpoint of the antenna as
possible - usually mounted on the boom of the antenna.
Jim - KR9U
-----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.
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