Hi Jim,
If you base load a 68 vertical on 160 meters it will create very
high voltage at the base of the vertical which may damage the
base insulator. Much better to use top loading to avoid high
voltage at the base.
73
Frank
W3LPL
----- Original Message -----
From: "Jim Garland" <4cx250b@miamioh.edu>
To: topband@contesting.com
Sent: Sunday, September 2, 2018 10:03:32 PM
Subject: Re: Topband: Air wound coil
On this general topic, I'm erecting a 68 ft aluminum self-supporting
pole (DX Engineering) that is four inches OD at the bottom, tapering to
about 1/2 inch at the top. It is designed as a full size 1/4 wave 80m
vertical. I'd like to use it on 160m. If I add four capacity hat wires
at the top, would that sufficiently lower the resonant point? The
antenna tilts at the base with a hand winch, so it's not hard to add or
remove wires if I want to restore the antenna to 80m. The other option
is to add inductance at the base (easy to do), but I don't know if that
is the preferred solution or not. BTW, there are sixty 30m radials
already installed at the base, from a previous antenna. I only care
about resonating the antenna near the low end of the band. Except for
cacti and coyotes, the antenna is 200m from any structure, fed with
buried hardline. Any suggestions? Thanks!
73,
Jim W8ZR
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