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.

--

Rick

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.

Indeed it is and why do you worship Wikipedia.


w.

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.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

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

On Wed, 14 Oct 2015 20:38:23 -0400, rickman wrote:

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.

Yep. However, wrapping did improve the SNR a few dB, which is a sure
sign that I must have done something right.

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 gets worse, I just found this link, which says my explanation
doesn't work:
http://www.w8ji.com/magnetic_receiving_loops.htm
What little is mentioned about shielded loops claims that it does not
suppress the E-field and details how skin effect makes it work. I
gotta work through this again to make sure I understand it.

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

Yep. The author of the above article definitely agrees with that. It
may take me a while before I agree, but only after I understand how a
shielded loop really works.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

In message , Jeff Liebermann
writes
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...-if-anything-m
akes-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've a 5 foot Octagonal loop for MF. The shield is copper water pipe,
with a gap , 7 turns inside plus a coupling winding. It does a good job
eliminating local noise (mostly ASDL hash from the phone lines) compared
with a vertical. However the capacitance between the shield and turns
seems to load it quite a bit meaning I can't get the tuning range I'd
like.

Brian GM4DIJ
--
Brian Howie

On 10/15/2015 6:13 AM, Brian Howie wrote:
In message , Jeff Liebermann
writes
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...-if-anything-m
akes-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've a 5 foot Octagonal loop for MF. The shield is copper water pipe,
with a gap , 7 turns inside plus a coupling winding. It does a good job
eliminating local noise (mostly ASDL hash from the phone lines) compared
with a vertical. However the capacitance between the shield and turns
seems to load it quite a bit meaning I can't get the tuning range I'd like.

I assume there is nothing to space the wires from the pipe other than
the insulation. Maybe you could use wire with thicker insulation? Or
if you are using straight pipe, could you use a fabricated spacer at the
corners? I guess that might be hard to assemble with soldering the
joints.

--

Rick

In message , rickman
writes

I've a 5 foot Octagonal loop for MF. The shield is copper water pipe,
with a gap , 7 turns inside plus a coupling winding. It does a good job
eliminating local noise (mostly ASDL hash from the phone lines) compared
with a vertical. However the capacitance between the shield and turns
seems to load it quite a bit meaning I can't get the tuning range I'd like.

I assume there is nothing to space the wires from the pipe other than
the insulation. Maybe you could use wire with thicker insulation? Or
if you are using straight pipe, could you use a fabricated spacer at
the corners? I guess that might be hard to assemble with soldering the
joints.

No just the insulation. It was hard enough to thread it without spacers
..

I should have stuck to the original design that used plastic pipe with
aluminium foil stuck to the outside

Brian GM4DIJ
--
Brian Howie

On 10/16/2015 6:53 AM, Brian Howie wrote:
In message , rickman writes

I've a 5 foot Octagonal loop for MF. The shield is copper water pipe,
with a gap , 7 turns inside plus a coupling winding. It does a good job
eliminating local noise (mostly ASDL hash from the phone lines) compared
with a vertical. However the capacitance between the shield and turns
seems to load it quite a bit meaning I can't get the tuning range I'd
like.

I assume there is nothing to space the wires from the pipe other than
the insulation. Maybe you could use wire with thicker insulation? Or
if you are using straight pipe, could you use a fabricated spacer at
the corners? I guess that might be hard to assemble with soldering the
joints.

No just the insulation. It was hard enough to thread it without spacers .

I should have stuck to the original design that used plastic pipe with
aluminium foil stuck to the outside

I saw one receiving antenna made from a bicycle rim. Easy to thread. I
assume you only use this for receiving?

--

Rick

"Brian Howie" wrote in message
...

I've a 5 foot Octagonal loop for MF. The shield is copper water pipe, with
a gap , 7 turns inside plus a coupling winding. It does a good job
eliminating local noise (mostly ASDL hash from the phone lines) compared
with a vertical. However the capacitance between the shield and turns
seems to load it quite a bit meaning I can't get the tuning range I'd
like.

Brian GM4DIJ
--
Brian Howie
Hi
My own experience is that ,at least for receive, multi turn loops are
useless.
Instead you can use a single turn one with a good coil in serial.
The tuning range for a given variable capacitor is much greater
especially if ,at low frequency, the coil is using ferrite .
Switching the coil can increase the tuning range easily.
The coil, with a secondary winding,is also very useful to
adjust the coupling to the receiver.