Topband: K9AY Center support

[K9AY]

> Gary,
> 
> What about the center support?
> I have answers from everyone with conflicting input.
> W8JI says it doesn't matter
> K6SE says it does...
> Would a metal center support interfere with the performance of the  loop?
> 
> Tom Baugh
> AE9B
----
Tom and fellow Topbanders,

My modeling exercises suggest that a grounded metal mast will 
degrade the pattern significantly. It will still have some F/B, but the 
peak F/B in the null will be reduced. Even if the NEC model over-
estimates the degree of coupling, it is a simple matter to use an 
insulated mast or lift the base of a metal mast off ground with some 
type of insulator. Because the model predicts this possibility of
degradation, I have never considered using a grounded metal support 
(and thus, have never tested the model on this particular issue).

Nearby grounded metal structures (towers) as short as 40 feet can 
have a detrimental effect on the pattern -- depending on the distance 
from the loops and the electrical height including antennas, guy wires,
etc. The effect of a specific installation are highly variable. I have had
inverted-Ls that virtually "disappeared" electrically during RX, but
a 40M dipole that had to be moved to keep the vertical feedline from
screwing up the pattern of the RX loop.

Do your best to locate the RX antenna as far from the TX antenna as
practical, and where it will be pointed away from the TX antenna when 
listening in your most important direction. Learning to de-tune a TX
antenna is worthwhile skill to develop, too!

73, Gary
K9AY