In a message dated 3/20/02 7:07:59 PM Pacific Standard Time,
n8de@thepoint.net writes:
> > You only need to get it 30 feet or so off the ground to minimize
ground
> > capacitance effects.
>
> Thirty feet? .. for 20m? That's not even 1/4 wavelength, and hardly a
> good place to measure ..
All we're trying to do is minimize ground capacitance effects.
I've probably installed over 100 ham antennas and have measured most of
them in the air before they were installed. My two favorite installation
techniques are using a tramline or a crane. Either way allows as many
iterations and measurements as you want. I've found that once you get above
30-40 feet, additional height doesn't change the resonance enough to worry
about.
> besides, the feedpoint of the 205CA is NOT near
> the mast, so would require some real gymnastics effort to get to it for
> true resonance measurements.
The tramline or crane makes the location of the feedpoint irrelevant. I
have a length of RG8-X that I attach to the balun, clove hitch to the boom,
then hoist the antenna up and measure.
Cheers,
Steve K7LXC
Tower Tech -
Professional tower work for amateur radio operators
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