On 10/14/2015 3:23 PM, Jeff Liebermann wrote:
On Wed, 14 Oct 2015 14:34:10 -0400, rickman wrote:

I just read the wikipedia article on small loop antennas and it seems I
was laboring under a misapprehension. I thought receiving loops were
"magnetic" because they were shielded (this is often stated in various
web pages about constructing such loops). But the wikipedia article on
small loop antennas says the nature of a small loop is to not be very
sensitive to the E field in near field.

So if the shield has little to do with rejecting near field electrical
noise, what does the shield do? A lot of antenna designs make a big
deal of the shield. So I assume it must be a useful addition to the
small loop antenna for some purpose.

The shielded loop reduces local noise pickup by eliminating much of
the electric component of that noise in the near field. Since the
ability of a small loop antenna to hear properly is primarily an
exercise in improving the SNR, any reduction in noise levle, without a
corresponding reduction in signal level, is a very good thing. More
detail:
http://electronics.stackexchange.com/questions/70262/what-if-anything-makes-shielded-loop-antennas-so-great-at-rejecting-local-nois

I've built small loops that were not shielded and measure the SNR of
some stable signal, such as WWV. I then wrapped the loop in aluminum
duct tape, leaving a gap to prevent a shorted turn problem, retuned,
and found that the baseline noise level had decreased and the SNR had
improved. It works.

I hope you realize that your experiment is not at all conclusive since
wrapping the duct tape around your loop changes many things other than
just adding a shield. Those other effects may or may not improve any
given loop antenna.

Do you understand the details of how such a shield should work? The
link you provided gives several conflicting opinions on this including
one very detailed post which claims there is little or no suppression of
the E-field, rather it is only the nulls that are useful.

It was finding posts like this that have made me doubt the suppression
of the E-field by the shield.

--

Rick