To: <topband@contesting.com>
> Date: Wed, 29 Apr 1998 08:38:18 -0500
> From: Lee Buller <k0wa@southwind.net>
Hi Lee,
> Someone mention chokes on dipoles. I have used current chokes on beams, but
> never on 40, 80 and 160 dipoles. Can someone illuminate me on the whys and
> wherefores concerning current chokes on feedline to the dipole? I hae read
> the articles in QST, but what practical experiences do we have out there in
> the collective wisdom of the reflector.
I use chokes because they prevent the feedline from arcing over to
the tower legs or other cables, as well as the more common reasons.
I had two experiences where this occurred.
One was with a 160 droopy dipole. I had an insulated feedline running
down a tower leg, and about 90 feet down from the dipole it arced
through the insulation and paint to the tower leg.
Another was with my 20 meter yagi, a bit less than 1/4 wl from the
feedpoint the coax arced from shield to mast causing TVI.
A coil of coax, much like Roy Lewallen describes in his articles,
cured it.
By the way, when I measured FS from elevated radials, there was
almost a one dB decrease in FS when I omitted a choke balun and
allowed the elevated radial common point to terminate to earth via
the feedline, plus I had feedline radiation. With a bunch of radials,
the choke made no detectable change.
Choke baluns can help with verticals using poor grounds, and I also
use them on my receiving antennas to prevent noise ingress from
common mode currents.
73, Tom W8JI
w8ji.tom@MCIONE.com
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