RadioBanter - View Single Post

November 9th 04, 12:23 PM

(Richard Harrison) wrote in message
The secret to noise immunity is symmetry and balance
in all aspects of the loop.

Exactly. But to me, there is no such thing as noise immunity as far as
far field noise. The only noise that really can be reduced, is any
possible common mode related noise due to lack of a balun device,
whatever, at the feedpoint. And that assumes you actually have shack
noise to reduce. Not all do. IE: using a loop out in the middle of the
woods with a battery radio, etc...You can change polarity to reduce
maybe 20 db or so, but thats another issue...As far as far field
noise, the only way to reduce, is to ensure better balance. Better
balance gives you deeper nulls, and hence, lower noise, IF!, you are
using the loop to *NULL* the noise source. If you don't turn the loop
to null the noise source, it will be just as noisy as any other loop.
But as mentioned, this good balance can be attained with unshielded
loops also. As far as I can tell, and I have tested this in the real
world, balance is what separates a good loop from a medeocre loop. Not
a shield, etc.
The split shield is just one method used to provide good balance.
Thats why they are often used for DFing. With good balance, the nulls
will be sharp, and there will be little skewing of the pattern. None
of the shielded loops I've tried were any quieter to far field noise
than my unshielded loops. Other than small differences in signal
strength due to size, turns differences, the overall s/n ratio was the
same. I could not hear anything on one loop, that couldn't be heard on
another due to any increase or decrease in s/n ratio. In other words,
all my loops act pretty much the same, shielded, or unshielded. MK