[TowerTalk] beam antenna patterns; groundwave

[Jim Jarvis]

Folks,

While I agree with Tom, in theory, that all manner of localized
effects can come into play, mapping pattern using groundwave at
far-field has SOME value.   I did it routinely in Vermont, with a
station 5 miles away.  We had hills and trees in between.  What came
back was quite close to claimed specification.

To be sure, the groundwave pattern isn't the same as that at real arrival
angles.  But it allowed me to estimate f/b on both an lpda and a steppIR,
and to do it against a co-located vertical antenna.  The vertical was used
as a frame of reference.   The technique also allowed me to properly
decouple
the feedlines.  When we first started, I had a 6dB f/b on my vertical!
Adding common mode chokes and running the coax down separate tower legs
tamed that beast.


n2ea
jimjarvis at ieee.org