On Mon, 8 Nov 2004 09:58:10 -0800, "Joel Kolstad"
wrote:

Will the current on the inner conductor be identical to the case
where there is no shield? Is there any current on the shield? Does
anything change if I ground the shield?

Hi Joel,

A 1M loop in a 1Hz field, Hmm?

Why bother with the complication of shielding? Take a 1M loop of
wire, connect it to your MOST sensitive ammeter (mine will resolve at
least 1 nanoampere).

By simply going to my lab, and turning on the unit, this allowed me to
test my hypothesis as leads that long were already attached.

I used the earth's magnetic field and a nearby fluorescent fixture (80
W) to find absolutely NO sensitivity at all on AC or DC scales
(turning the loop in earth's magnetic loop to simulate the lower 1Hz
frequency you specify).

Now, I know that for studies of low frequency magnetics, the usual
antenna has 10 to 20 thousand turns on an 18" ferrite bar, I think
that a 1M open air loop is destined for deafness.

Of course, this will serve as no impediment to those who can count
angels on the head of a pin, so your question will undoubtedly be met
with great fuss.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
A 1M loop in a 1Hz field, Hmm?

That was meant to setup the problem such that the loops is electrically
small and such that only quasi-magnetostatic analysis would be necessary.
In actuality I'm thinking more along the lines of WWVB loop antennas --
60kHz.

Why bother with the complication of shielding?

The idea is that there's a lot of predominently electric field interference
around (60Hz power lines, for ones) and that the shield -- if grounded --
can short out that component of the field and get the loop to respond
primarily to the magnetic field.

---Joel

On Mon, 8 Nov 2004 10:53:06 -0800, "Joel Kolstad"
wrote:

"Richard Clark" wrote in message
.. .
A 1M loop in a 1Hz field, Hmm?

That was meant to setup the problem such that the loops is electrically
small and such that only quasi-magnetostatic analysis would be necessary.
In actuality I'm thinking more along the lines of WWVB loop antennas --
60kHz.

Hi Joel,

When I was calibrating my Atomic Clock, years distant, my antenna was
a simple 20' whip above the fantail of my ship. We used WWVB and an
unique modulation envelope to perform the job. This didn't make the
antenna particularly efficient, but it was suitably sensitive. Still
and all, there are roughly 5 orders of magnitude down to the 1Hz
region.

You may as well use WWVB as your testbed, or one of the submarine
fleet frequencies around 12KHz. One station is nearby here at Jim
Creek. They use a T antenna of about 1000' tall with a top hat of 6
cables strung between two mountain tops (about 4000 to 6000 feet
between them). The numbers may be off, but you can judge that the
scale is impressive (quite a sight).

Why bother with the complication of shielding?

The idea is that there's a lot of predominently electric field interference
around (60Hz power lines, for ones) and that the shield -- if grounded --
can short out that component of the field and get the loop to respond
primarily to the magnetic field.

1Hz noise field would come from meteors striking, and ionizing the
upper atmosphere. I doubt you could judge against any local sources
of noise compared to that chatter. Given that line frequency would be
6 Octaves away, if you tuned your antenna (it would be tuned, wouldn't
it?), you would have to be next to a noisy power plant to hear it.

73's
Richard Clark, KB7QHC
73's
Richard Clark, KB7QHC

That's some interesting history Richard!

"Richard Clark" wrote in message
...
1Hz noise field would come from meteors striking, and ionizing the
upper atmosphere. I doubt you could judge against any local sources
of noise compared to that chatter. Given that line frequency would be
6 Octaves away, if you tuned your antenna (it would be tuned, wouldn't
it?), you would have to be next to a noisy power plant to hear it.

Well, I've read that down around 60kHz there's plenty of interference due to
noise on the power lines (I doubt harmonics, probably just plain old noise
from, e.g., switching power supplies). But in any case, I'm at the point
where I need to just build something and see how it performs.

---Joel