Topband: Mounting feed wire inside the tower on a shunt feed.

[Gary Breed]

Ken and all,

Think about this setup for a moment -- you would create a transmission line
that was shorted at the top, with the shield grounded at the bottom. The net
result is that all you have is a wire inside a shield. See Gauss' Law.

To radiate, we need current to flow on the outside of the shield (the
tower). The arrangement described cannot radiate unless you have, by design
or by accident, a break in the shield of this transmission line, or large
gaps in the shield structure that allow coupling from inside to outside.
Badly corroded leg joints might do the job and create an inefficient
radiator.

One option is a wire vertical (think big -- a 4-square) that uses the tower
for support.

I have modeled, but have no experience with, routing the shunt wire past an
antenna by feeding it close to, or in the center of the tower for a short
distance above and below the offending antenna. The model suggests that it
will work OK, and it should be easy to try.

73, Gary
K9AY





--
FAQ on WWW:               http://www.contesting.com/topband.html
Submissions:              topband@contesting.com
Administrative requests:  topband-REQUEST@contesting.com
Problems:                 owner-topband@contesting.com