I've got a used HyTower vertical I'm putting up. Its got the 160M coil at the
base but I don't care for that system for 160 because you have to manually
switch between 160 and 80.
After reading Bill/AA4LR's email below and looking at his blog about the shunt
fed tower I thought the switchable LC network at the base of his shunt fed
tower is just what I need!
Is there a commercially available, switchable matching device that I could use
at the base of the HyTower that will allow me to switch from 160M to 80M
without running out to the base of the tower to switch it? Something capable
of handling a KW would be great but something smaller would be good to.
Thanks for your help!
Gary Slagel
Hot Springs, SD
N0SXX
http://marina.fortunecity.com/sanpedro/351
--- On Sat, 4/30/11, Bill Coleman <aa4lr@arrl.net> wrote:
From: Bill Coleman <aa4lr@arrl.net>
Subject: Re: [TowerTalk] [Bulk] 160m Shunt Feed
To: "Kelley" <kshaddrick@jetup.net>
Cc: towertalk@contesting.com
Date: Saturday, April 30, 2011, 5:22 PM
On Dec 11, 2010, at 6:57 PM, Kelley wrote:
> 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?
It really depends on the shunt-feeding arrangement. Some can get by with a
single shunt capacitor, others use an omega match, still others use L or T
networks.
It really all hinges on the complex impedance that shows up at the feedpoint.
I have a short tower that I have shunt-fed for 160 and 80m. It works pretty
well. Just about any installation is unique though -- how tall is the tower,
how big are the antennas at the top, how high and how far away is the shunt
wire(s), etc. K9AY suggested I run a shunt wire as high as I could, and then
measure the impedance at the base and build a matching network to suit. And
that's what I did, basically.
You can read the entire article on my blog here:
http://boringhamradiopart.blogspot.com/2009/04/shunt-feeding-short-tower-on-80-and.html
I didn't have any sophisticated equipment to measure the impedance, so I
designed an L-network through trial and error.
If you want to run more than 100 watts or so, you are likely to need pretty
beefy components in the matching network. Capacitors with 1-4 kV ratings
recommended. Coils (if you need them) would be very large.
Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr@arrl.net
Web: http://boringhamradiopart.blogspot.com
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
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