Actually, Jerry, the real reason for it is
to isolate the antennas from each other...more
than to protect the coax from lightning discharge.
In a direct strike, you can pretty much kiss anything
on the tower goodbye, anyway.
But feedlines run down 60' of tower, whether taped to
the sameleg, or opposing legs, will have some measure
of coupling. You don't want that.
In VT, I had a beam, and a vertical 10' above it.
The feedlines came down the outsides of separate legs.
There were coil-chokes in both feedlines at the
antennas.
The vertical exhibited a 6dB f/b ratio, when I rotated
the system.
To eliminate it, I installed ferrite chokes topside, ran both
coaxes adjacent to each other, down the inside of one leg...
but tied shields to ground, top and bottom, and then had
ferrite chokes again, coming off the tower. The result was
good isolation, and no more f/b.
N2EA
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|