Topband: A 160 Meter antenne puzzle

[Tom W8JI]

> Is it really necessary to isolate the vertical from the pressure treated 4 
> x
> 4 with PVC tubing and is it really necessary to install a 1:1 balun 
> between
> the antenna and feedline in this 4-square receiving array?

In this case the antenna was base loaded and pretty short (30 feet = .05 
wavelengths), so anything around the antenna above the base loading can have 
a large effect. It really should be spaced a few inches away from any wooden 
pole because the impedance and electric field is so high.

If the impedance was lower, it could be nailed right to the pole with no ill 
effects. It has almost nothing to do with leakage resistance. The problem 
really is the poor and grossly changing dielectric near the high impedance 
area of the antenna.

It is always a good idea to fully isolate the feedline when using a small 
radial system, or when fairly strong common mode noise is present on the 
feedline shield.

73 Tom