On Sep 27, 7:48 pm, "Dave" wrote:


Again, I think you are describing the loop shown in Fig 3 of my article.
You don't need to use coax for the loop itself, it is not a balanced loop
as described and coax doesn't help with balance. If it was you intention
that the loop was not susceptible to pickup on the feedline, the antenna
you describe does nothing to prevent that. The shielding explanation for
that type of loop is bunk.

Owen

Okay, well, all I am trying to do is build something that will pick up weak
signals from a given direction, while ignoring signals and noise from other
directions. Ideally, it would not introduce a great deal of noise from any
source (unlike the loop I currently am experimenting with.) I am not overly
enamored of complex designs, and don't really care what it looks like so
long as it meets the above criteria. Do you know of any fairly simple
designs that would meet this description? If tuning is possible, that would
be a plus.

Thanks,

Dave

One thing about small loops.. They are great at nulling ground wave
signals,
but not so great at nulling skywave signals.
So how well a small loop would work will depend on the source of the
noise.
If the source is local, IE: a noisy power line, etc, that signal will
arrive via
a space or ground wave, and you can null that noise very well.
But if the interference is via sky wave, you might get a reduction in
strength,
but usually not a total null.
As a general rule, small loops are best suited to the lower
frequencies.
They work ok for the HF bands, but you may not the see all the
benefits
on those bands that you might on the MW bands. But even one used
for HF should get a decent null on a noise signal as long as the
source
is fairly local.
As far as shielded loops, I've carefully compared both unshielded and
shielded loops, and couldn't really tell a lick of difference as long
as
both are balanced. I've also tried using unshielded loops, but with a
shielded coupling loop. Again, no difference, as mine are fairly well
balanced even using a regular unshielded solenoid loop.
I had just as deep nulls unshielded, as I did shielded.. No difference
in perceived noise either. So I consider using shielded loops an
option,
but usually not needed. As many have mentioned , the only advantage
is to help ensure balance, and in most cases, it's not a problem to
worry about.
I do mount everything very symmetrically though. I make mine with
very simple PVC frames.
IE: one example... http://web.wt.net/~nm5k/loop5.jpg
But my big one is even more simple. Just a thick appx 2-3 inch PVC
"mast", and regular 3/4 inch PVC for a cross arm, using PVC "Tees"
at the ends to thread the wires through.
The 3/4 inch PVC crossarm is run through drilled holes in the larger
PVC
mast. I drill them to fit tight, and I don't even have to glue them,
although
thats an option. I use stands to mount the loops on, and they can be
easily turned.
MK