Yuri Blanarovich wrote:
. . .
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?

Sorry, you're not making much sense to me. You said that a non-ferrous
shield is transparent to a (time-varying) magnetic field. The
experiments I proposed illustrate that this is false. This has nothing
to do with what name you attach to a shield.

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.

Hm. How do you know it's from just the magnetic field?

This is really interesting. Just a couple of postings ago, you said that
a non-ferrous shield is transparent to a magnetic field. Now you say
that a magnetic field is heating your body. Do you have some embedded
steel shrapnel or something making your body ferrous, or do you just eat
lots of nails and scrap metal?

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?

What has? The heating? That's due to the lossiness of bodily fluids in
the presence of either time-varying magnetic or electric fields.

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?

If you'll read what Tom has posted, or a description in any good text,
you'll find that the whole circumference of a "shielded" loop radiates.
The field comes from current on the outside of the "shield", not from
some field penetrating the shield. That's my theory. It's the same as
Tom's, and that of every respected author I've read.

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

Reality proves Newton wrong -- any fool can see that moving objects come
to rest on their own. There's no conflict between theory and reality --
just between theory and people's interpretations of what they're seeing.

I'll stick with the theory that's been known and confirmed for over a
century. People with alternate theories, like yours, will have to
provide some extraordinary proof to sway my thinking.

It seems you're more interested in proving Tom to be wrong about
something -- anything! -- than taking the effort to really understand
what's actually happening. So nothing else I can post will help you. I
hope the lurkers have gotten something from this, though.

Roy Lewallen, W7EL

I suspect
that no two people here on r.r.a.a are in 100% agreement
on everything.

Surely you jest... Fight! Fight! Fight! Kinda reminds me of
Beevis and Butthead after eating too much chocolate..
K7ITM pretty much boiled it down to the raw minerals by
noting that the usual "shielded loops" only advantage is the oft
improved balance. I've already been through all this mess testing
them here...
And I've proven to myself that an open wire loop can be just as
good as a "shielded loop" just as long as balance is taken care
of. It's the balance that matters. If the two types are equally
balanced,
and the same size, they will act the same.
The rest is just fodder for bored old farts on a newsgroup.
Of course, many won't agree with me, and this would include Yuri,
since he believes a shielded loop is quieter than an open loop.
But I don't care.
It's a free country. Or I think it is... Sometimes I wonder these days

with all these goofballs we have in DC running the show.
MK

Cecil Moore wrote:

I suspect
that no two people here on r.r.a.a are in 100% agreement
on everything.

I disagree! heh ;^)

- 73 de Mike KB3EIA -

Roy Lewallen wrote:

If you'll read what Tom has posted, or a description in any good text,
you'll find that the whole circumference of a "shielded" loop radiates.
The field comes from current on the outside of the "shield", not from
some field penetrating the shield. That's my theory. It's the same as
Tom's, and that of every respected author I've read.

Game, Set, and Match, Roy. The explanation and the everyday application
of the concept of non-ferrous shielding are both simple and elegant.

Seems like the thread stopper to me! I suspect it will continue
anyhow.... 8^)

- 73 de Mike KB3EIA -

Mike Coslo wrote:
The explanation and the everyday
application of the concept of non-ferrous shielding are both simple and
elegant.

I'm fairly ignorant when it comes to shielding. Do the
magnetic fields from a magnet penetrate copper? Do the
magnetic fields from 60 Hz devices penetrate the shield
on coax?
--
73, Cecil http://www.qsl.net/w5dxp

wrote in message
oups.com...

And I've proven to myself that an open wire loop can be just as
good as a "shielded loop" just as long as balance is taken care
of. It's the balance that matters. If the two types are equally
balanced, and the same size, they will act the same.

Sooo, in shielded loop the shield is the antenna according to W8JI and
worshippers. But you take the shield (W8JI antenna) away, now the wires are
antenna, some say don't need no stinkin' shield and "antenna" to work as an
antenna.


The rest is just fodder for bored old farts on a newsgroup.
Of course, many won't agree with me, and this would include Yuri,
since he believes a shielded loop is quieter than an open loop.
But I don't care.

Amazing how selective in reading and digestion of postings some people are.
They tend to ignore the reality and description of it, they pick on
selective "proof" of what they were taught and figered out.
I emphasize, that electrostatic shield on the loop antenna is effective on
close proximity radiation, within some fractions of a wavelength from the
source of interference/signal. It does not (significantly) affect band noise
or distant noise/signals. Anyone who can build shielded loop and test it
within local arcing source or test transmitter, can see the attenuation of
the said noise.
So shield works as a electrostatic shield, if you guys like it or not, or
refuse to admit.
It is not that I believe in that, I have experienced it, seen it, measured
it and it works, it is there and anoyne can verify that, contrary to
"theories" of those who "figured" it can't be.
Electrostatic shields work on principle of capacitance plate, being grounded
and side exposed to electrical/electrostatic fields shunting the field to
ground. Capacitor's one "plate" is the interference/signal source
(antenna) - other "plate" is the el. static loop shield, grounded, shunting
electrical fields to ground and preventing from entering the antenna.
(Something like that).

Sooo, antenna works without shield (not just my assertion), but when you
insert it in the shield then shield becomes W8JI antenna. So his shield,
untuned becomes antenna, but my tuned and tunable inside the shield antenna
is not the antenna? Makes as much sense as "there is equal current along the
loading coil doesn't matter what", riiiiight?


It's a free country. Or I think it is... Sometimes I wonder these days
with all these goofballs we have in DC running the show.
MK


We were better off with Clintonistas having orgies in WH while Bin Ladin
turbanites were running around, blowing up Americans and using our flight
schools, our planes to demonstrate their "religion of peace" in NYC WTC
inferno?

Let's stick to some reality in antennas.

Yuri, K3BU

On Wed, 17 May 2006 11:30:55 -0400, "Yuri Blanarovich"
wrote:

Electrostatic shields work on principle of capacitance plate, being grounded
and side exposed to electrical/electrostatic fields

There's a very simple test of this "shield." It relates to experience
and doesn't need for you to go to the library.

1.) Tack a wire across the gap.

Q. Do you still have signal?

A. No!? None????

Extra Credit Question:
Did the wire make the "shield" better, or worse?

73's
Richard Clark, KB7QHC

p.s.
from your experience, the answer to the initial question above may
vary. If in fact it does, it may bring new material for discussion.

"Mike Coslo" wrote in message
...
Roy Lewallen wrote:

If you'll read what Tom has posted, or a description in any good text,
you'll find that the whole circumference of a "shielded" loop radiates.
The field comes from current on the outside of the "shield", not from
some field penetrating the shield. That's my theory. It's the same as
Tom's, and that of every respected author I've read.

Game, Set, and Match, Roy. The explanation and the everyday application of
the concept of non-ferrous shielding are both simple and elegant.

Seems like the thread stopper to me! I suspect it will continue anyhow....
8^)

- 73 de Mike KB3EIA -

Before you pronounce your verdict, why don't youze guyze build the shielded
loop antenna as I described and test it. Try version without shield, see
what IS antenna, and try the same antenna with shielded loop. Then run
electric drill or another source of arcing or interference in the vicinity
and see if there is shielding effect or not. Then pronounce your verdict and
pontificate on how electrostatic shields suppose to work. Otherwise you look
silly like W8JI cult worshippers.

73 Yuri, K3BU

"Richard Clark" wrote in message
...
On Wed, 17 May 2006 11:30:55 -0400, "Yuri Blanarovich"
wrote:

Electrostatic shields work on principle of capacitance plate, being
grounded
and side exposed to electrical/electrostatic fields

There's a very simple test of this "shield." It relates to experience
and doesn't need for you to go to the library.

1.) Tack a wire across the gap.

Q. Do you still have signal?

A. No!? None????

Agree!
That makes it Faraday shield, which stops any signal from entering inside of
the tubing.
I never asserted that Faraday shield or closed metallic enclosure passes any
signals or fields.
We are talking about electrostatic shield, which if removed, antenna works
without change, you put it back, it still works the same way plus it rejects
in its reactive near field region electrical field interference.
If it was to be antenna, then when removed, the rest should stop working as
an antenna, or what is the theory?

Extra Credit Question:
Did the wire make the "shield" better, or worse?

It turned it to Farady shield and prevented signals from exciting the
antenna inside.

Extra Credit Question for professor:
Q1: If electrostatic shield is added to small loop antenna and it attenuates
the interference or signals from its vicinity, does it perform the function
of a shield or antenna?
Q2: Can the piece of tubing that is grounded by its outside surface, acts as
a capacitor's plate and provide the path to ground for electric field in
vicinity?

73's
Richard Clark, KB7QHC

p.s.
from your experience, the answer to the initial question above may
vary. If in fact it does, it may bring new material for discussion.

I just wish that points of discrepancy were addressed, rather than parties
taking off on tangents fitting their convinctions and trying to weasel out
of the wrong statements.

73 Yuri, K3BU

On Wed, 17 May 2006 12:17:07 -0400, "Yuri Blanarovich"
wrote:

Extra Credit Question:
Did the wire make the "shield" better, or worse?

It turned it to Farady shield and prevented signals from exciting the
antenna inside.

It's still the same "1/2 inch copper water tubing (non ferrous
material passing the magnetic field)."

So, does that wire make the "shield" better, or worse?

Super-extra credit question:
If we replaced the non ferrous material (same gap, no link) with (most
have probably anticipated this) a ferrous material, does this allow
near field region electrical field interference to pass un-impeded?

73's
Richard Clark, KB7QHC