Date: Wed, 21 Dec 2011 12:46:24 -0500
From: K8RI <K8RI-on-TowerTalk@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.
## whoa ! On my F-12 6-el 15M yagi, it's a Direct 50 ohm feed set up,
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
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
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
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
## One fellow I know abt 400 miles east of me... had static build up so bad on
that it was arcing across, a real mess.
Later........ Jim VE7RF
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