[TowerTalk] Re: Driv Elem Tuning

[Roger]

Someone (I think that it was Brian Beezley, K6STI) suggested a few years
ago that HF beams may be tested before installation by pointing them
straight up in the air with the reflector just a few feet off the ground.
I have heard from many hams who have tried this, and it seems to work well.
This simulates an antenna installation height of more than 70 feet on the
bands 40-10 meters.  The only thing that may cause problems is wires,
fences, etc. parallel to the beam elements near ground-level.

As far as fine-tuning the DE with the antenna on the tower, I don't have
any problem with this.  A change in length of a single DE has very little
impact on gain, F/S or F/B as long as the efficiency and match remain the
same or improve.  A change of a few inches of a DE at HF is reasonable.
However,  I would not recommend fine-tuning a DE in a log-periodic dipole
array, dual-driven array or an open-sleeve without some guidance.

I also do not recommend adjusting parasitics without knowing what effect it
will have on the beam.  Lengthening a reflector or shortening a director
will usually produce a broader VSWR curve, but it also affects the F/B and
gain too.  Computer programs such as YO, NEC, AO, etc. can give you some
guidance here if you have an accurate model.

73 Roger WB0DGF
Telex Communications, Inc.
http://www.hy-gain.com



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