Topband: Shunt fed tower

[Tree]

On Thu, Apr 22, 2010 at 03:20:51PM -0400, Phil LaMarche wrote:

> Several weeks ago Herb out lined his recommendations for shunt feeding a
> tower and recommended it over the inverted L.  I have an L with the apex 55
> ft.  My tower is 72 ft with a large Mosley Pro 67C at the top. I lost his
> email.  Any recommendations?  He recommended 3 wires vs. one wire.

A 72 foot tower with a big antenna at the top is pretty much exactly what I was
using for a transmit antenna to get over 200 countries from the west coast.  It
is very easy to make that work on 160 meters and if you have nice flat ground
around you for a few wavelengths that isn't lossy - you should end up with a 
very good signal.  

I have matched it using some RG8 or even RG6 as a gamma "rod" - spaced about
2 or 3 feet from the tower - with the attach point up around 55 feet.  You will
need about 300 pf at the bottom.  Use a variable cap until you prove you have a
solution - then some RG8 as a capacitor (with the shield spread out from the center
conductor at the end of the cap).  

I wouldn't ever bother with an inverted L in your situation as you would likely 
need to first detune the tower to make the wire work.  It's far easier just to 
load the tower and be done with it.  No broken wires to deal with and if you
invite a friend over to see your killer 160 antenna - they can't even find it.

Tree N6TR