Mark Keith wrote,

Tdonaly wrote:



Yes, but does your small, inefficient, shielded loop improve the
signal-to-noise
ratio in the directions of its maximum gain over say, a non shielded loop?

Many claim this, but I didn't see it when I compared them. I found a
shielded coax loop just as susceptible to local, and not so local noise,
as a non shielded loop assuming both are balanced. This is not counting
the feedline, or any common mode currents unbalancing the loops. Both
are capable of very sharp nulls. No difference really, and both are good
at nulling a noise source. But a shielded coax loop quieter than a
regular loop? I don't see it. It's not the loop itself, or having a
shield. It's the keeping of good balance. The shielded loop design and
method of feeding forces a good balance. But if you have a regular loop
that is also just as balanced, I maintain it's just as "quiet". To me,
this "shielded loop being quieter" theory is an old wives tail of sorts.
My two favorite MW loops are both unshielded. Ones a 16 inch dia circle
with 12 turns, and my big one is a diamond with 44 inches per side. "5
turns". Both are on floor stands indoors, and rotate.
I've tried using shielded coax loops, and I saw no reduction of noise.
I've also compared using both shielded and non shielded coupling loops
to feed the loops. Again, no difference in noise levels. MK

--
http://web.wt.net/~nm5k



This pretty much squares with an article on shielded loops written by
Glenn S. Smith of the Georgia Institue of Technology in _The Antenna
Engineering Handbook_. He says the shield enforces symmetry so that
the pattern doesn't suffer, and that's what it's supposed to do. No mention
of noise at all.
73,
Tom Donaly, KA6RUH