Topband: Shunt-feeding

[Gary Breed]

I must agree with Mauri.  All conductors going up the tower should be
at the same potential to minimize RFI and avoid having those cables
become part of the matching (mis-matching!) circuit.  If all cables enter 
the tower structure at the base, you might be close, but the only 
guarantee is to attach the shields to the tower at the point of lowest 
potential (ground). Ideally, you would bypass the rotator conductors
and other control cables!  Tying cables so they lie tightly against tower 
members is the second best solution, but try to ground things first.

Also, grounding cables (or their shields) at the tower base helps route
static discharges to ground without creating voltage differentials that
may propagate into the shack.

73, Gary
K9AY
----------

> Mauri, I4JMY wrote:
> 
> "... although better if also the yagi fed element is grounded (hairpin)
> in most cases there is not an absolute need to ground it to the boom if
> the yagi coax runs tightly with the tower legs and its shield is grounded
> at the tower base."
> ==========
> I always recommend that shunt-fed tower users tape the beam coax (and
> rotator cable) to a tower leg on its way down to the ground.  This indeed
> couples the driven element to ground and incrases the top loading effect
> if that element is not hairpin (beta-match) fed.  I disagree that the
> beam coax should be grounded at the base of the tower, however.
> 
> 73, de Earl, K6SE