[TowerTalk] SWR Problem Balun or lightning protection?

[Jim Thomson]

Date: Wed, 21 Dec 2011 12:46:24 -0500
From: K8RI <K8RI-on-TowerTalk at tm.net>
Subject: Re: [TowerTalk] SWR Problem Balun or lightning protection?

On 12/21/2011 10:30 AM, Chuck wrote:
> I like gamma matched beams because you don't need a balun and there is no DC
> short to ground at the antenna.  You can check for shorts and high
> resistance paths to ground from the shack.

That DC short to ground is one of the best things about them.  IE, no 
static build up.


73

Roger (K8RI)

##  whoa !    On my  F-12  6-el  15M yagi,  it's a Direct 50 ohm feed set up, like
an OWA  yagi.   Just a 17"  long bead balun, made from large type 43 beads, slid
over RG-393 teflon coax.   There is NO hair pin used on these types of yagis, so
it's NOT dc grnded.   The way to get around that is to either [A]  install a 35 uh
choke across the feedpoint, [like 12 ga magnet wire on a  torroid, like ICE uses
inside their lightning arrestors]   of [B]  install a  35 uh choke  between 
hot and chassis on your amp output, right at the coax output. [dunno why amp
maker's don't do this already, I do it on all my hb amps] . All amps
already have a safety choke across the load cap, but it's only in the circuit on 
TX.   Alternately, an ICE lightning arrestor, or just a 35-50uh choke, from
hot side of coax to grnd , any where on the feedline, will do the trick. 
You could even install the 35-50uh choke inside  a remote switch box, on the
input. 

On my AS  remote switch box, they use a mess of  DPDT open frame relays
with 10 kv stand off.  It's configured, such that all de-energized ant ports
have their center conductor's DC grnded..   Gamma  match's  are great..except
when the DE  is  a mile out from the tower.  Even on those, you can still use a 
35-50 uh choke.   The 12 ga magnet wire on a torroid type is nice, since 12 ga
wire is pretty robust.  You can also get 10 + 8+ 6 ga magnet wire from planet wire.  

##  One fellow I know abt 400 miles east of me... had static build up so bad on his yagi
that it was arcing across, a real mess.  

Later........ Jim   VE7RF