"K7JEB" wrote in message
news:GrQvc.45743$mm1.6092@fed1read06...
I was hoping someone else would jump in and answer, but
here goes anyway...

Eric Schumacher, WB6KCN, asked:

Can anyone give me a brief explanation of the theory
of operation of a commercial FM broadcast antenna.
Specifically the Jampro JMPC. Picture at:

http://www.jampro.com/fma/jampjmpc.htm

It looks to me like a couple of 1/2 wave dipoles
each folded into V and fed in phase using two gamma
matches. If this is true I am puzzled by the tap
point chosen. It seems further along the dipole
than I am used to seeing, even considering that the
feed for the dipole is likely 100 ohm. The feed
must be very inductive.

When the ends of a dipole are folded back, the radiation
resistance decreases and matching schemes have to become
more extreme. The Jampro antenna does not look that
exceptional to me. You're probably right about a certain
amount of reactance accompanying the feedpoint resistance.
This could be tuned out by a matching network hidden in
the feedline/support pipe.

Given the above analysis: Also note that one of the elements is quite
close to the supporting structure nearest its high current center.
--
Steve N, K,9;d, c. i My email has no u's.