You guys discussion prompted me to look into the "counterpoise" for horizontal
wire antennas. I found a brief article here, including some graphs.
73 de Bob - KØRC in MN
Date: Sun, 09 Sep 2007 01:40:53 -0500
From: K4SAV <RadioIR@charter.net>
Subject: Re: [TowerTalk] putting a reflector below a 75 meter inverted
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
A wire on the ground gets tuned to a lower frequency by being on the
ground, so to act like a reflector (and tuned to a lower frequency) it
has to be shorter than a half wave dipole. You only get a benefit from
doing this when the antenna is very low to the ground. For an 80 meter
dipole at 15 ft, you can pick up about 3 dB with three reflectors on
average ground. For an inverted vee at 95 ft the gain increase should
be less than 0.3 dB.
If you use a single wire not on the ground below the antenna, then the
reflector has to be longer than when on the ground, but it still gets
detuned by ground, and the optimum length is still likely to be less
than 0.5 wavelengths (maybe 0.498). You didn't say what the included
angle of your vee was, but the spacing should probably be around 0.125
wavelength from average height of the vee. With the right length
reflector you may be able to get about 1 dB more gain straight up.
Probably less across the whole band. Get the reflector the wrong length
and you can have a huge gain decrease.
Joe Barnes wrote:
>I am using an inverted vee at 95 feet and am contemplating putting a
>reflector below it for a close in chatting. I believe that the reflector
>needs to be 5% longer than the inverted vee but what should the spacing
>be? I was told tonight to just lay the reflector on the ground but that
>makes no sense to me. Thank yall for your help
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