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

Richard Harrison wrote:
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."

Richard.

I know anything Roy Lewallen agrees with, you disagree with. I know
anything I say (or even what I don't say) sets Yuri off into a foaming
lather. I really wish you guys could put personal hate or dislike aside
and look at facts. This is an imporant issue because the myth about
shields is imbedded in amateur circles despite many clearly written
engineering texts and very simple experiments that prove the concept of
time-varying magnetic fields penetating the shield. It's just a fact
when the time-varying electric field is taken to zero so is the
time-varying magnetic field.

Static by definition is not moving or varying. Don't confuse jargon
describing a different coupling mode with the mechanics of a loop
operating at radio frequencies.

When we receive noise or signals, the fields are time-varying. Just as
with a piece of coaxial cable, the inner wall of a "shielded loop" is
isolated by the skin depth of the conductor from the outside wall. The
electric and magnetic coupling effects are what causes a coaxial cable
with a dense shield more than a few skin depths thick to ALWAYS have
the same current on the inside of the shield as the inner conductor
has, and all radiation or common mode current flow over the outside.

This isn't something I invented. It has been in nearly every textbook
long before I was born.

I'm pleased that Yuri credits me for the work, but unfortunately I had
little to do with it. It really was people from the 1700's and 1800's
that did all the work.

You (and Yuri) appear to be confusing how time-varying fields work.

I suggest you put Terman aside and actually read some textbooks on
fields.

It's helpful to actually make a few measurements. A few minutes spent
with some very simple test equipment would go a long way to "turning on
the light".

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

If you say so. And as one, it also must block any time-varying magnetic
field. As K7ITM points out it is the gap in the loop that is actually
the feedpoint, and it is the outside of the loop that is the actual
antenna.

If you do not think a loop behaves this way, you need to get busy doing
some real important work. You need to get all the Handbooks to quit
talking about common mode currents on shield outsides. You need to get
them to quit treating the inside of the shield as a isolated conductor
that is independent of the outside.

As I and others have suggested it only takes a moment to prove the
books are correct. You can prove it with a single sheet of copper and a
minimum of test equipment.

73 Tom

wrote in message
ps.com...

Richard Harrison wrote:
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."

Richard.

I know anything Roy Lewallen agrees with, you disagree with. I know
anything I say (or even what I don't say) sets Yuri off into a foaming
lather. I really wish you guys could put personal hate or dislike aside
and look at facts. This is an imporant issue because the myth about
shields is imbedded in amateur circles despite many clearly written
engineering texts and very simple experiments that prove the concept of
time-varying magnetic fields penetating the shield. It's just a fact
when the time-varying electric field is taken to zero so is the
time-varying magnetic field.


That really nails it! His "technical" response!
Perfect picture of a jerk parading as an engineer!
Yep, I hate your guts and I made up phony claims on your web site for all to
see, so I can "hate you"! Brilliant! Keep it up!
Halleluja, now we know that shields are antennas, praise the guru!


Bada BUm

wrote:
I know anything Roy Lewallen agrees with, you disagree with.

Absolutely false. I'll bet they agree on 99% of technical
topics, e.g. ohm's law, Maxwell's equations, etc.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
wrote:

I know anything Roy Lewallen agrees with, you disagree with.


Absolutely false. I'll bet they agree on 99% of technical
topics, e.g. ohm's law, Maxwell's equations, etc.

Just like arguing whether Coke or Pepsi tastes best. The closer the
product, the worse the arguing...

- 73 de Mike KB3EIA -

Tom, W8JI wrote:
"This is an important issue because the myth about shields is embedded
in amateur circles despite many clearly written engineering texts and
very simple experiments that prove the concept of time-varying magnetic
fields penetrating the shield."

Some of that poison reached the 2006 ARRL Handbook on page 13.18. Fig
13.26 says:
"Electrostatically-shielded loop for RDF. To prevent shielding of the
loop from magnetic fields, leave the shield unconnected at one end."

Terman`s RDF loop should have better balance than ARRL`s because
Terman`s shield gap is squarely in the center of the loop
and not at one end. However, as long as the shield is broken preventing
induced current from flowing around the shield, Lenz`s law will be
thwarted and magnetic coupling to the coil under the shield will be
obtained. Electric field coupling to the coil beneath the shield will be
disallowed by the shield`s connection to ground wherever it occurs,
though not as elegantly as when care is taken to get the best balance
possible.

I`ve worked with such Faraday screens in my broadcasting career.

Best regards, Richard Harrison, KB5WZI