"Roy Lewallen" wrote in message
...
I haven't gone through this in detail yet, but one misconception is
glaring:

Yuri Blanarovich wrote:
. . .
I used 1/2" copper water tubing (non ferrous material passing the
magnetic field) for circular loop about 4 foot diameter. . .

If you believe that, it's no surprise that you're having difficulty
understanding how a shielded loop works.

It's not hard to demonstrate that the (time-varying) magnetic field
doesn't penetrate a non-ferrous shield, if you believe (correctly) that a
time-varying magnetic field will produce a current on a nearby conductor.
Simply put an oscillator or signal source into a copper box -- you can
solder one op out of PC board material. Run some wires all around the
inside which carry the oscillator signal, putting them as close to the
shield wall as you like. Put a battery inside the box to power the
oscillator and seal the box up. Then sniff around the outside of the box
with any kind of magnetic field detector you can devise. If you have a
little potted oscillator of some kind, you should be able to do this in a
couple of hours at most.

That is called Faraday shield and does not function as Electrostatic shield.

Or, just connect your rig to a good dummy load with some double shielded
coax and sniff around the outside of the copper coax shield. If you put
the detector just outside the shield, the current on the inside of the
shield will be much closer to the detector than the current on the center
conductor. So if the shield is transparent to a magnetic field, your
detector should go wild. (Make sure the rig is very well shielded, though,
so no common mode currents make their way from the rig to the outside of
the shield.)

Alternatively, if you'll spend some time with a good electromagnetics text
learning about eddy currents and the like, you'll understand why you'd be
wasting your time with those experiments.

I learned about shieldings, Faradyas, I use them, in equipment design, in RF
and harmonics suppression, I built shielded room for university. But I also
know the difference between the Farady shield and Electrostatic shield and
seen them work. Maybe lumping all shields is as no good as lumping all coils
ain't no good?

Once you're convinced that the shield blocks the magnetic as well as
electric field, you'll have to revise your theory on how a shielded loop
works. And you'll find that Tom's explanation is correct.

Roy Lewallen, W7EL

Roy,
I have magnetothermia machine which is about 200 W push-pull power generator
at around 27 MHz. It uses single turn, shielded loop, made of coax, about 30
inch in circumference. Loop wire, antenna (center conductor of coax) is fed
from the plates of two tubes, shield is open at the far end and grounded at
the exit from the enclosure. I get those 200 W heating my body tissue with
magnetic field. Maybe it has something to do with shielding being a fraction
of a wavelength distance from the radiator and the properties of the
magnetic and electric components in the antenna reactive near field region?

I know that this loop radiates along its circumference, not just from the
gap in the shield. What's yer theory? Or it don't (ooops, can't) woyk?

You seem to associate and stick to wrongos and I am sorry you find their
explanations correct, for the reality proves them wrong.

73 Yuri Blanarovich, K3BU