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
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