Yuri Blanarovich wrote:
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?

Yuri,

A shield is a shield.

People made some very good posts explaining how the "shield" works, and
there was nothing wrong with my original explaination.

You stated the shield is an "electrostatic" shield and I pointed out a
static field does NOT cause noise. Static is by definition stationary
or non-varying.

The only reason the shield affects the noise, as I and others have
pointed out, is the shield changes the balance of the system. The
shield IS the actual portion of the antenna that receives the signal,
whether that signal is noise or an intentional desired signal.

The entire shield can be dispensed with without any change in the
system so long as the system remains in balance, and that is quite
possible to do.

As a mater of fact if a non-symmetrical "shield" is added over a
balanced system it will decrease balance and make the system more
susceptable to noise because the feedline will become part of the
actual antenna.

You might look for a copy of "Fundamentals of Electricity and
Magnetism" (McGraw-Hill). This entire book deals with basic field
behavior and entire chapters explain in detail what everyone is saying.

As Roy pointed out, I didn't make this stuff up. It has been in print
since the 1800's and the electric field effects first experimented with
around 600 BC (although it was the 1600's before serious experiments
were done).

There's nothing impossible about what you may have observed but the
reasoning you gave and statements about my explaination being in error
are wrong.

There is absolutely nothing that causes noise to electric field
dominant and the shield absolutely does not "filter" the time-varying
electric field from the time-varying magnetic field. The shield IS the
actual antenna and the stuff inside it, once inside it, is excited only
by the gap. Nothing at frequencies of interest passes through the
shield walls.This is a very well-known behavior and why so many
immediately disagreed with your description.

73 Tom

Yuri, K3BU wrote:
"Electrostatic shields work on principle of capacitance plate, being
grounded and side exposed to electrical/electrostatic fields."

Terman on page 1049 of his 1955 edition writes:
"Such a shield ensures that all parts of the loop will always have the
same capacitance to ground irrespective of the loop orientation in
relation to neighboring objects."

Yuri is consistent with Terman, and that is liable to be better than a
bible because it is provable and demands no faith. If wrong, it will be
rewritten with corrections.

Best regards, Richard Harrison, KB5WZI

Yuri Blanarovich wrote:
"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.

Yuri, you is way too intense! I don't pontificate, and my silliness is
genetic, not involved in any worship of W8JI.

I very much expect that any effects that you see may be due to another
cause than what you attribute it to. I don't know if your antenna is not
completely shielded along it's entire circumference or not. I wonder if
you could put your antenna inside a Faraday cage and see different
results. Perhaps even try the unshielded antenna in the Faraday cage.

Unshielded antenna in cage should equal shielded loop in open. If it
doesn't, I'd look for a problem in the experiment first, not a problem
in the theory.

- 73 de Mike KB3EIA -

Yuri Blanarovich wrote:
"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.

Makes it a short!

I never asserted that Faraday shield or closed metallic enclosure passes any
signals or fields.

Aren't both conditions shields?. One just has a short.

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.

Give it a few more posts, Yuri, and it will turn into standing waves in
coils again!! ;^)

- 73 de Mike KB3EIA -

On Wed, 17 May 2006 13:46:39 -0500, (Richard
Harrison) wrote:

Yuri is consistent with Terman, and that is liable to be better than a
bible because it is provable and demands no faith. If wrong, it will be
rewritten with corrections.

Hi Richard,

It is one thing to run a Xerox, it is another to apply it to one
particular howler that has Yuri stumped:

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

Tom, W8JI wrote:
"There is absolutely nothing that causes (sic) noise to electric field
dominant and the shield absolutely does not "filter" the time-varying
electric field from the time varying magnetic field."

A "Faraday shield" is designed to allow magnetic field coupling while
disallowing electric coupling. See page 38 of Terman`s 1955 edition:
"It is possible to shield slectrostatic flux without simultaneously
affecting the magnetic field by surrounding the free space to be
shielded with a conducting cage that is made in such a way as to provide
no low-resistance path for the flow of eddy currents, while at the same
time offering a metallic terminal upon which electrostatic flux lines
can terminate."

I`ve previously described the Faraday picket fences or Faraday screens
used in the medium wave broadcast stations where I worked that were used
to avoid capacitive coupling to the antennas while permitting magnetic
coupling. Capacitive coupling would favor harmonics of the operating
frequency. These are undesirable. The Faraday screen effectively rejects
the capacitive coupling. It shorts the lightning strikes to ground too.

In a Faraday screen one end of pickets or wires is grounded. Their other
ends are open-circuited. So, circulating current can`t flow through the
wires. Thus, no counter-field can be generated to oppose magnetic
coupling but capacitive flux lines land on the wires and are shorted to
ground. It all works very well.

Look at Terman`s shielded loop on page 1048 of his 1955 editiomn.
There`s a gap in the shield opposite the feedpoint. The gap prevents
current circulation in the loop shield thereby making it permeable to
magnetic coupling while shorting the electric field to ground.
Therefore, this loop cover is a Faraday screen.

Why should we care if noise comes from near or far? The near field has 3
components. See "TV and Other Receiving Antennas" by Arnold B. Bailey.

The first near field component is produced by the electric vector and
decays by the cube of the distance. The second is the induction field
and decays as the square of the distance. The third is the radiation
field electric vector which becomes the volts per meter at a great
distance. This decays inversely with distance and its power decays as
the square of the distance. 6 dB every time the distance doubles.

Point is we don`t have to get very far from a noise source to make a big
improvement in noise received, especially if we avoid electric field
coupling which decays especially fast in the near field.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Yuri is consistent with Terman, and that is liable to be better than a
bible because it is provable and demands no faith. If wrong, it will be
rewritten with corrections.


If you read what has been said here very carefully you will find Yuri
claims the shield "blocks electric fields" or stops "electrostatic
fields". This is the effect of a Faraday cage or shield.

I did not claim that effect. Terman certainly did not. It is a folklore
or Ham-myth that only appears in amateur circles.

What others (including Terman exactly as you quoted) are trying to
tell Yuri is the shield ONLY affects balance. The shield IS the actual
antenna element that does the radiating. That is written in a half
dozen engineering good engineering references. That is how ANY shield
behaves.

Read he

http://en.wikipedia.org/wiki/Faraday_cage

or he

http://members.aol.com/omlcgm/deteck...gy/faraday.htm

or any of dozens of other places. Unless an off-the-wall hobbyist
publication or rouge opinion, you will see everyone agrees.

What Terman said is absolutely correct. The "shield" (when properly
constructed) balances the capacitance of the antenna to earth. It does
not "stop" the electric field. It certainly does not filter a
time-varying electric field because doing so would by definition of
Maxwell's equations (which everyone who isn't a CFA or EH antenna quack
agrees are true) also stop the time varying magnetic field.

As everyone (including Terman) has tried to explain, the shield only
affects balance. The shield HAS to be the actual antenna element
because by definition of ALL the peer-reviewed textbooks published to
date as well as any description of coaxial cables the inner shield wall
is isolated from the outside by the skin depth of that wall.

This is so very simple to prove, it only takes a moment. It doesn't
even take exotic test gear. These experiments were done in the 18th
century with very crude instruments.

You can take a solid copper sheet for example and place a small loop
antenna near that "wall". If you probe current on the wall near the
loop on the loop side, you will find a current maximum right under that
loop. VERY easy to see. 100% repeatable.

Now if you move the probe to the other side of the wall you will find
current MINIMUM at the sheet center and increasing towards two of the
edges.

This is a TOTALLY open wall with no seal, it isn't even a box.

Shields a few skin depths thick are a virtually perfect barrier to both
magnetic and electric fields. This is true for densely woven coaxial
cable shield or even thin aluminum shields, metallic sheets, or any
good conductive wall.

Saying Terman supports anything to the contrary only proves someone is
misquoting or misunderstanding plain English, since Terman is a very
clear writer. There is no way Terman failed basic physics and his peer
reviewed textbooks are wrong.

Yuri may need to read some basic textbooks, I'd be happy to copy the
applicable pages if there isn't a good library nearby. It is essential
to get the basics down solid.

73 Tom

"Richard Harrison" wrote in message
...
Yuri, K3BU wrote:
"Electrostatic shields work on principle of capacitance plate, being
grounded and side exposed to electrical/electrostatic fields."

Terman on page 1049 of his 1955 edition writes:
"Such a shield ensures that all parts of the loop will always have the
same capacitance to ground irrespective of the loop orientation in
relation to neighboring objects."

Yuri is consistent with Terman, and that is liable to be better than a
bible because it is provable and demands no faith. If wrong, it will be
rewritten with corrections.

Best regards, Richard Harrison, KB5WZI


Richard,
thanks for the reference and support, coming from one who had his hands
"dirtied" with the antennas.

Terman also says just a sentence befo
"Errors from unbalance can be minimized by using circuit arrangements
that are symmetrical with respect to ground, such as shown in Fig. 26-27b.
It is also helpful to enclose the loop in an electrostatic shield, such as
metal housing broken by an insulated bushing, as show schematically in Fig.
26-27c."
and then sentence quoted above.

Clearly, the shield is functioning as an electrostatic shield, providing
symmetry and is not acting as "W8JI Antenna". Loops are the antenna, shield
is the SHIELD, contrary to W8JI proselytizing.
Small loops are the antennas, with or without the shield. Electrostatic
shield is a shield, provides symmetry for the antenna and helps to reject,
shunt the interference from the sources in the proximity of the antenna by
its virtue of the capacitance to the ground.
Terman didn't say: "yo stupid, you don need no stinkin' loops, jus' use the
shield as antenna" :-)))

73 Yuri Blanarovich, K3BU

Tom, W8JI wrote:
"I did not claim that effect. Terman certainly did not. (Yuri claims the
shield "blocks electric fields" or stops "electrostatic fields".)"

I`ll requote Terman from page 38 of his 1955 edition which Tom ignored:
"It is possible to shield electrostatic flux without simultaneously
affecting the magnetic field by surrounding the space to be shielded wih
a conducting cage that is made in such a way as to provide no
low-resistance path for the flow of eddy currents while at the same time
offering a metallic terminal upon which electrostatic flux lines can
terminate."

That is a description of the shield on Terman`s direction finding loop.
The loop has a gap in the shield opposite its feedpoint. The gap
prevents current from circulating around the loop shield and thus
prevents creation of an opposing magnetic field by the shield to the
incident field acting on the loop.

The grounded shield nevertheless terminates electric flux shorting it to
ground.

The loop shield is thus a true Faraday screen, not a Faraday car body or
screened room.

Best regards, Richard Harrison, KB5WZI

"Mike Coslo" wrote in message
...
Yuri Blanarovich wrote:
"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.

Yuri, you is way too intense! I don't pontificate, and my silliness is
genetic, not involved in any worship of W8JI.


Sorry! I didn't mean you specifically, jus' generally those who worship W8JI
gospels.

I very much expect that any effects that you see may be due to another
cause than what you attribute it to. I don't know if your antenna is not
completely shielded along it's entire circumference or not. I wonder if
you could put your antenna inside a Faraday cage and see different
results. Perhaps even try the unshielded antenna in the Faraday cage.

Of course it will not work, Faraday cage - shield, shields all RF.

Unshielded antenna in cage should equal shielded loop in open. If it
doesn't, I'd look for a problem in the experiment first, not a problem in
the theory.

It is electrostatic shield, not "shielded, closed" loop shield. Antenna will
still work the same inside the cage, just will not receive any signals if
they are not passed through the cage. I am not overthrowing legitimate
theories, I am describing what I observed and objecting to call the shield
an antenna, when it isn't!!!

- 73 de Mike KB3EIA -

I have no problem with theories, I have problem with silly claims that
shield is an antenna. I described my experiments, explained behavior and
performance of the shielded loop in the near field interfering
signals/noise.
Build it, if you have problem with local noise, you would see the benefit of
the electrostatic shield on the suppression of it and on symmetry and deep
nulls on other signals. Shield is a shield and not antenna. Rest of
mumbo-jumbo is twist away from the subject and attempt to legitimize
wrongoooo!

73 Yuri Blanarovich, K3BU