[TowerTalk] Isolated LPDA as toploading

[Jim Jarvis]

Jim, W5QM wrote:

"The question is this: The tower supports a Tennadyne T-12 12 element log
periodic antenna that is not electrically connected to the mast and
tower.....is there sufficient coupling to provide the needed toploading?"
==========

Earl, K6SE replied:

If all of the log-periodic elements are DC tied together and its feedline
runs all the way down to the ground inside the tower (or taped to one of
the tower's legs), yes, it will provide maximum top-loading.

+++++++++

To which I will append:

It depends on whether you take pains to isolate the
coax from the tower, before taping the run to the tower
leg.  In my case, ( A T8), I used a series of clip on ferrites to
isolate the antenna from the outside of the coax braid, and then
tied the shield to the tower, both topside and at the bottom.  
Never tried shunt feeding the 45G, but substantially improved 
the LPDA pattern by those steps.  

One way to go is a topside relay which ties the T12 coax to the 
tower top, when not energized.  Add 12v to the coax, and you've
got a beam.  (Look at an Ameritron RCS4 switch...it may do most of what you
want, without modification).   

N2EA
jimjarvis at ieee.org