I've never been all that fond of fan dipoles, but you can minimize the
interactions by running the two dipoles perpendicular to each other.
Obviously that works best with true dipoles ... inverted-V's would have
more interaction because of the additional vertical components.
One thing I played with for a while was feeding a 160m north/south
oriented inverted-V (apex at about 55 feet) at a point 25% from one
end. On 160m a low center fed dipole has a pretty low feedpoint
impedance, but at the 25% point it is higher ... close to 50 ohms in my
case. On 80m that same antenna and feedpoint acts like two half-waves
in line, still close to 50 ohms impedance but with the pattern off the
ends. It worked, but fixed north-south radiation on 80m isn't ideal,
and you'd have the same issue with perpendicular fan dipoles.
If I really wanted decent performance and pattern on both bands, I'd
probably pick a single dipole with a length somewhere between a half
wavelength for the two bands and use an efficient antenna tuner for both
bands. Just my bias ...
On 4/20/2011 10:53 AM, Mike Fatchett W0MU wrote:
> This might also be called a Fan dipole.
> Can you run 160 and 80 on the same feedline with decent swr? I have
> tried to model this and have not been very successful.
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