On Thu, 19 Oct 2006 12:25:30 -0400, Bill Gaines AD8P wrote:
>For several years now I have used a 65' tall "Tee" vertical on 160.
>It is an open wire fed 80 meter dipole with the feed point shorted
>and fed together. This is fed against 6 or 7 elevated 1/4 wave
radials.
Several thoughts. What I'm using is quite close to yours -- an 80/40
dipole fed with about 70 ft of 72 ohm kW twinlead (long out of
production) against 25 radials that are 70 ft long. I think it's
optimum on 80 (and works like it is), but could use some more height on
160.
So my next move will probably be a dedicated top-loaded vertical (I'll
move the dipole to different trees) for 160, but in the form of a fan
dipole using spacers. I think I can probably rig the top of the Tee to
about 100 ft between two trees, so one wire will be part of the Tee.
The other wire will be a quarter wave on 80, and I'll hook both of them
in parallel at the base. I'll probably use spacers that put the two
wires about a foot apart. I'm hoping to pick up a dB or two from the
longer radiator on 160. (Any predictions on that?)
Second thought. Elevated radials need to be a signficant fraction of a
wavelength above ground to provide the full benefit of elevating them.
See the ARRL Antenna Book and ON4UN's book for a discussion of this. So
the second thing I would do if I were you is to look seriously at your
radial system. You might find a few dB of improvement there. I've
bought some junk wire to improve my radial system, and expect to pick
up a dB or so by the time I'm done.
The combination of radials and taller vertical radiator has the
potential to give me something like 3 dB, which is equivalent to
doubling my transmitter power.
73,
Jim Brown K9YC
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