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[TowerTalk] Fwd: Terminate braid at top of tower...or not?

To: towertalk@contesting.com
Subject: [TowerTalk] Fwd: Terminate braid at top of tower...or not?
From: Hans Hammarquist via TowerTalk <towertalk@contesting.com>
Reply-to: Hans Hammarquist <hanslg@aol.com>
Date: Sat, 1 Nov 2014 09:01:49 -0400
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
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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