[TowerTalk] 80M and 160M Matching Network

[Gary Slagel]

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 at arrl.net> wrote:


From: Bill Coleman <aa4lr at arrl.net>
Subject: Re: [TowerTalk] [Bulk] 160m Shunt Feed
To: "Kelley" <kshaddrick at jetup.net>
Cc: towertalk at 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 at arrl.net
Web: http://boringhamradiopart.blogspot.com
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901

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