[TowerTalk] Vertcal Dipole

[Tom Rauch]

> Has any made a vertical dipole (lets say for 20
> meters) where it is end fed with coax.

Tom,

Why not make a trap at the bottom out of coax??? Use a 1/2
wl of coax as the radiator with the shield cut 1/4 wl back
from the open end.

Tie the shield and center together at the ends of the outer
section.

Like this:

_______        _______
I- - - - - I----------------Coax Shield Isolator --Feedline
_______        _______


You would have a symmetrical diameter dipole, and by winding
the coax in a nearly self-resonant solenoid and adding only
enough parallel C to make it resonant, you could get pretty
good isolation.

To make the isolator, you could wind RG174 in a single layer
and put a high voltage 20-50pF capacitor across it from
shield to shield at each end.  Adjust the turns spacing
until resonant.

I'd make the whole antenna out of RG-174 or similar. Two
isolators spaced 1/8th wl would be better.

73 Tom