[Antennas] vertical dipoles

[Cletus W Whitaker]

de WB2CPN South Central Pennsylvania   2002.07.13

The botton end of a vertical 1/2 wave dipole should be kept a few feet
from the ground, but it really needs to be higher in order to get a clear
shot at the horizion.  There are various ways to feed it in the middle,
if you want to get if higher. One is coax, which should run horizontal
for at least a 1/4 wave. Or, you can make a two-wire center fed dipole
which will approximately match 300 Ohm line (Impedance = Number of Wires
Squared, times 72). Try that with a 4:1 balun at the shack end.  I said
approximately, there's always more to most things if you want to look into 
them.  You can make it a three-wire dipole and have a approximately 600
ohm feed.  If you want to feed it at the bottom end you will need a high 
impedance source, something like a Johnson Match Box, or a Pi network of 
some kind.  The tuner has to be right at the end of the dipole, and the 
distance between the tuner and ground should be short(?).  Vertical 1/2 wave
dipoles use a ground differently than the way a 1/4 wave uses a ground. 
They need a reflective surface or good ground in the near-field.  If you use
radials, use a lot and don't bury them too deep.  You'll know if they are
working if your signal is not effected much by snow, rain, or drought.
                   73  Clete