[Top] [All Lists]

[TowerTalk] 160m Shunt Fed Tower

Subject: [TowerTalk] 160m Shunt Fed Tower
From: Kelley <>
Date: Sat, 08 Oct 2011 15:47:42 -0500
List-post: <">>
I have a 48 foot free standing tower. At the top is a Cushcraft A3S 
3-element tri-bander with the 40m add-on kit. About 5 feet above that is 
a 3-element 6m beam. About 2 feet above that is a 2m/440 vertical. Also 
at the top of the tower about 1 foot out is the apex of a 80m inverted V.

On the opposite side of the tower from the 80m inverted V is my shunt 
wire. It is attached at the top of the tower and runs the entire height 
of the tower. It is about 18 inches away from the tower. It is a single 
14 gauge stranded wire.

There are 46 65' radials at the base of the tower spread out over 180 
degrees from north thru east to south. The area to the west of the tower 
is blocked by the house so I can't put radials there.

I have been unable to get any kind of reasonable match on this setup. 
I've tried a variety of variable capacitors and coils in various 
configurations with no luck.

Connecting my MFJ-259B to the shunt wire and ground and adjusting for 50 
ohms of resistance, I get a frequency of 9.145 MHz, R=50, X=46, and SWR 
= 2.2.

Setting the frequency to 1.8 MHz, I get a R=0 (it seems to stay at zero 
no matter what frequency I set it at until I get close to 9.145 MHz), 
X=637, and SWR = >25.

To be honest, I don't really know what these numbers are telling me. The 
folks who taught me to build antennas only looked at SWR. Low SWR good 
to go. None of this R and X stuff. I suppose with dipoles one might get 
away with this, but this antenna seems to be a different game.

I'm looking for some ideas on what direction to head. I'm open for any 
suggestions. Is the wire too close to the tower? Too far away? Do I need 
more wires? Is this tower configuration just not suitable for a shunt 
fed antenna? What additional data might you need to determine what's 
going on here?

Thanks for any input you might have,

-- Kelley - WØRK

TowerTalk mailing list

<Prev in Thread] Current Thread [Next in Thread>