On Dec 13, 3:01*pm, Sébastien MEDARD wrote:


We get writers here who pound the table because their magic loop in the
shack is noisy and their long wire 10M away in the back yard is quiet.
They have to be told to turn off the flourescent light in the shack if
they want their magic loop to work.
* *(Their magic loop low score on Amazon) = (stupid.)

Lesson one = learned.

Thanks.

Sebastien.

One thing handy about a small loop is you can turn it to
null out the offending noise. Like Richard says, there is no
magical quality which provides lower noise vs any other
antenna. The real benefit is being about to turn it, usually
while in the listening position. If the loop is well balanced,
the nulls are quite sharp and deep and in many cases you
could make that nasty noise source vanish. You can also
turn it to receive multiple stations that are on the same
frequency. You null the one you want to get rid of.
But these type of loops are best suited for the low bands.
LW, MW are where they are best suited. You get much
better nulls off a ground wave signal, than you do one
that is propagated via skywave. So they tend to work
better at nulls in the daytime vs at night. At night, you
get a mix of ground and sky wave, and the nulls are not
as deep. In the day, I can make most ground wave
signals totally vanish by nulling them out.
These can be used in the SW bands, but don't expect
the deep nulls, being as most all SW will come via sky wave.
For general SWL, you are usually better off with the various
wire antennas. Random wires, dipoles, etc..
But I recommend a small loop for MW if you want the
ability to null noise or undesired stations.
Most of mine, I build from PVC tubing for the frames.
I have one in this room that is a diamond, 42 inches
per side. It's on a stand which allows it to rotate, and
it stands almost as tall as the ceiling. But they don't
have to be that big. I've got another round one that is
about 16 inches across, and it works very well too.
Just a tad less signal than the big one. But the s/n
ratio is much the same for the majority of the stations
listened to.
http://home.comcast.net/~nm5k/loop5.jpg
This is my usual favored method for building a low cost
MW loop. The hardest part to come by these days is
the variable cap. I dig them out of old radios, and old
analog tuning stereo receivers. Those are some of
the best ones to use, as they often have several
gangs which can be wired in parallel for more
capacitance, or deleted for less. For the upper
tuning ranges of the loop, it's best to delete most
of the gangs, and use one of the very small ones
by itself.
That way you get a smaller value, and will increase
the upper tuning range, vs just turning all the gangs
in parallel to the minimum setting. So I use switches
to do this quickly.
But if you can't find any old radios to acquire the
variable caps, you can buy them online from a few
places. I wouldn't use one any less than a dual
365pf BC cap. You can wire the two gangs together
for 730 pf. With careful loop turn design, you can
usually cover the whole MW BC band with one of
those. But I prefer the ones out of old stereo receivers.
They are even better, and can give a wider tuning
range. I think the one on my big loop has four or
five gangs, some being small and useful for upper
end tuning, if the other larger gangs are switched out.