Topband: Noise problems, please your help is needed

[Tom Rauch]

Edy,

We Hams sometimes come up with some very strange ideas. One 
popular false idea is that noise is electric field dominant 
and that good signals are magnetic, and that a small loop 
magically "shields" or sorts the "good magnetic signal" from 
the "bad electric field noise".

This is all a very deeply seated false myth that keeps 
getting repeated.

The ONLY thing a shield on a loop does, other than 
mechanically holding the loop up, is to make it easier to 
electrically balance the antenna. Sometimes an improperly 
designed shield makes the loop balance much worse!

I have some explanations at:

http://www.w8ji.com/receiving.htm

in particular

http://www.w8ji.com/magnetic_receiving_loops.htm



It sounds like you need a way to null the signals from below 
the antenna. A good small loop properly constructed turned 
on the flat side with the axis up and down would do that, 
but the null is very narrow!! It is so narrow one antenna 
often does not null noise much.

You could be more successful to position two small loops 
equally spaced perhaps 50-75 feet apart with 180 degree 
phase shift. Years ago I had to do this at a commercial 
installation in a 30 story office building. This will give a 
vertical null that is much wider than  one loop would have. 
The loops must be placed in line with the desired 
directions, so you may need two systems to cover all 
directions.

I would stay away from any elongated loop like a flag or 
pennant or K9AY. They would probably only be good if you 
covered the roof with a dense shield screen!!

73 Tom