Kelley:
The two-capacitor matching system is probably the Omega match. This
matching system is typically used on towers that are longer than 1/4
(electrical) WL. Most of us mere mortals are confined to feeding shorter
towers.
If that is the case, you can most likely use a single capacitor of
appropriate voltage rating as part of a Gamma matching system. This is a
single large gauge wire (think CATV coax sheath) or a wire cage of several
parallel wires supported off the tower by a couple of feet or even more and
tapped onto the tower somewhere near the top. The capacitor (usually a
transmitting variable but can also be a fixed value, once the proper value
has been obtained) is connected at the bottom of the tower between the end
of the shunt wire/cage and the center of the coax cable. The coax shield is
connected to the tower itself and to the radial system emanating from the
tower.
Once you have the wire tapped and capacitor connected, you start the
game of adjusting the cap for minimum SWR, then changing the tap point on
the tower if you can't get the match low enough. This may take a few trips
up and down the tower before you get a decent match.
You can check out KB9CRY's tower and shunt feed at
http://nidxa.org/kb9cry_shunt_fed_tower.htm . Mine is pretty similar
including the wire cage on PVC supports off the tower.
73 de
Gene Smar AD3F
----- Original Message -----
From: "Kelley" <kshaddrick@jetup.net>
To: <towertalk@contesting.com>
Sent: Saturday, December 11, 2010 6:57 PM
Subject: [TowerTalk] 160m Shunt Feed
> Multitudes of web pages show, well, multitudes of setups for shunt feeding
> a tower. Many appear to use a couple of variable capacitors in order to
> adjust for lowest SWR. Having a limited junk box, what kind of parts
> should I be looking for to build a generic matching network?
>
> Thanks,
>
> Kelley
> _______________________________________________
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