Jim Kelley wrote:

Hi Roy -

It's certainly true that a moving charge generates a magnetic field, so
perhaps I'm reading it wrong. But it appears to me that Mr. Bailey is
arguing here that an electron cannot be compelled to move simply by the
application of an electric field. Do you think that is what he is
saying? Do you agree?

No, I don't believe he's saying that. He says,

The small electric vector acts on the internal electrons of
the conductor and impresses a direction force, tending to drive the
electrons along the skin of the conductor in the direction of the
electric vector. . .

Roy Lewallen, W7EL

Roy Lewallen wrote:
Jim Kelley wrote:


Hi Roy -

It's certainly true that a moving charge generates a magnetic field,
so perhaps I'm reading it wrong. But it appears to me that Mr. Bailey
is arguing here that an electron cannot be compelled to move simply by
the application of an electric field. Do you think that is what he is
saying? Do you agree?


No, I don't believe he's saying that. He says,

The small electric vector acts on the internal electrons of
the conductor and impresses a direction force, tending to drive the
electrons along the skin of the conductor in the direction of the
electric vector. . .

Yes. But then he goes on to say,

How, then, is the electric vector from the electromagnetic wave going to put these electrons in motion?

That's what I was referring to. Do you understand why he would pose
this question if he believed he had already given the answer in the
paragraph you quoted? He shoulda quit while he was ahead maybe? ;-)

Thanks,

Jim Kelley, AC6XG

On Mon, 28 Nov 2005 12:15:30 -0800, Jim Kelley
wrote:

How, then, is the electric vector from the electromagnetic wave going to put these electrons in motion?

That's what I was referring to. Do you understand why he would pose
this question

As already stated:
But from experience we know that /no/ electrons can
ever be caused to move without gradually establishing their own magnetic
field, and this usually takes /time/.
The need for time (impedance) is accommodated by the wave:
It can only do so because the electromagnetic wave
/also supplies a magnetic vector/ as well as an electric vector.

The phase of the re-radiated signal is a function of the path length.
If the path signal required the electric potential to sustain movement
(no other motive force available), that would add an additional phase
retardation that is not observed.

Observation of what does occur is other wise described by Bailey as
from experience we know....

Roy's quote comes from a nascent discussion of the topic of Reception
that has a complete, later chapter devoted to it.

73's
Richard Clark, KB7QHC

Jim Kelley wrote:

Roy Lewallen wrote:

Jim Kelley wrote:


Hi Roy -

It's certainly true that a moving charge generates a magnetic field,
so perhaps I'm reading it wrong. But it appears to me that Mr.
Bailey is arguing here that an electron cannot be compelled to move
simply by the application of an electric field. Do you think that is
what he is saying? Do you agree?



No, I don't believe he's saying that. He says,

The small electric vector acts on the internal electrons of
the conductor and impresses a direction force, tending to drive the
electrons along the skin of the conductor in the direction of the
electric vector. . .


Yes. But then he goes on to say,

How, then, is the electric vector from the electromagnetic wave going
to put these electrons in motion?


That's what I was referring to. Do you understand why he would pose
this question if he believed he had already given the answer in the
paragraph you quoted? He shoulda quit while he was ahead maybe? ;-)

Well, it's obvious that an electric field can move an electron. The
Lorentz force law tells us how much force results from a given E field,
and we can get the resulting acceleration from Newtonian physics. An
everyday example is an oscilloscope deflection system which uses an
electric field to deflect electrons. (Actually, modern digital scopes
typically use raster displays with magnetic deflection -- but many of
still have older analog types with electric field deflection.)

But if the antenna conductor were perfect, no E field at all could exist
at the wire surface regardless of the amplitude of the E field of the
oncoming wave. The wave's E field therefore couldn't directly influence
the electrons in the (perfect) conductor. Only the H field of the wave,
then, can induce a current in the perfect conductor. The direct
influence of the E field on an imperfect conductor would be highly
dependent on the conductivity of the wire, and I'd guess it would be
very small compared to the influence of the H field from a typical
oncoming wave on an electron in a good conductor. Maybe that's what he
was saying.

Roy Lewallen, W7EL

Roy, W7EL wrote:
"But, if the antenna conductor were perfect, no E field at all could
exist at the wire surface regardless of the magnitude of the E field of
the oncoming wave."

If we have a non-varying E field, a perfect conductor in the field would
have the same voltage everywhere due to the short-circuit connecting all
points.

But, an electromagnetic wave sweeping the wire has an alternating
electric field. Its phase is uniform (the same) across the wavefront
because all points are equidistant from the source. A wire parallel to
the E vector would simultaneously experience the same E field force
throughout its length. "No E field at all could exist at the wire
surface regardless of the magnitude of the E field of the oncoming
wave,"

Why must the wire be perfect?

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Roy, W7EL wrote:
"But, if the antenna conductor were perfect, no E field at all could
exist at the wire surface regardless of the magnitude of the E field of
the oncoming wave."

If we have a non-varying E field, a perfect conductor in the field would
have the same voltage everywhere due to the short-circuit connecting all
points.

But, an electromagnetic wave sweeping the wire has an alternating
electric field. Its phase is uniform (the same) across the wavefront
because all points are equidistant from the source. A wire parallel to
the E vector would simultaneously experience the same E field force
throughout its length. "No E field at all could exist at the wire
surface regardless of the magnitude of the E field of the oncoming
wave,"

Why must the wire be perfect?

A time-varying E field can exist in a non-perfect conductor; it cannot
exist in a perfect conductor. You can find the explanation for why this
is in any electromagnetics text.

Roy Lewallen, W7EL

Roy Lewallen wrote:
"You can find the explanation for why this is in any electromagnetic
text."

I found it in Terman.

As we all know, we place correctly polarized dipoles, for example,
parallel to the wavefront for maximum response. Terman confirms the
electric field in this instance induces no energy in the antenna. It all
comes from the magnetic field.

If antenna current flows, no matter where it comes from, loss resistance
causes a voltge drop. That`s why the wire needs to be perfect. The
electric field produces no voltage in the antenna because the wavefront
has the same voltage across its entire surface. That`s because it all
left the same point at the same time. So, a wire parallel to the front
has no difference of potential induced by the wavefront`s electric
field. It all must come from the mgnetic field.

On page 2 of his 1955 edition, Terman says:
"The strength of the wave measured in terms of microvolts per meter of
stress in space is also exactly the same voltage that the MAGNETIC FLUX
(my emphasis) of the wave induces in a conductor 1 m long when sweeping
across this conductor with the velocity of light."

From the above, it is seen that the electric field is not effective in
inducing current in a receiving antenna parallel to a wavefront. All the
energy intercepted by the antenna is induced by the magnetic field.

Best regards, Richard Harrison, KB5WZI

On Thu, 1 Dec 2005 14:18:33 -0600, (Richard
Harrison) wrote:

Hi Richard,

If antenna current flows, no matter where it comes from, loss resistance
causes a voltge drop. That`s why the wire needs to be perfect.

For one, there is no such thing as a perfectly conducting antenna,
except where one might truncate precision and measure at D.C. Even
for a perfect conductor (absolutely no Ohmic loss), it still exhibits
radiative loss, and any current through this loss must exhibit a
voltage (the same one described by Terman). Perhaps you intended
this, but you fail to offer Rr, a significant component.

The electric field produces no voltage in the antenna because the wavefront
has the same voltage across its entire surface. That`s because it all
left the same point at the same time.

An electric Dipole exhibits a loci of points in space that has the
same voltage, broadside to the radiator. And this loci is orthogonal.
All paired points in 3-space (in the same polarization to the dipole)
exhibit a potential difference. True, at a great distance it may be
meager, but the common evidence of reception proves it is adequate for
detection and measurement. Your discussion above is for the
insignificance of phase difference at a distance.

From the above, it is seen that the electric field is not effective in
inducing current in a receiving antenna parallel to a wavefront. All the
energy intercepted by the antenna is induced by the magnetic field.

From your copy of Bailey, review the text, and reconcile his remarks.

For others following the original poster's query for a source of
discussion about the physics of reception:

I would suggest reading the chapter "The Theory of Signal
Interception" (all may be advised this chapter runs to 63 pages),
specifically the first two sections "How the Antenna Intercepts a
Signal," and "The Current Treatment" from which I will lightly quote
to amplify the comments above:

"This electrical resistance is not only due to electrical
conductivity of the metal of which the rod is composed but also
due to other factors.... the predominant resistance is, strangely
enough, largely due to the fact that no electrons can move on the
antenna surface without also sending radio energy back out into
space."

By the decimation of the problem of treating a large surface as many
small ones (segmenting the antenna) Bailey offers:

"At each point along this rod we can arbitrarily say that a small
but finite voltage acts."

Notice the "acts" which is an initiator or causative agent, not a
passive result. This is not to say such action is in isolation,
Bailey clearly observes that E/H are inseparable and he offers that
the wave bootstraps the antenna's response (the point of his emphasis
on immediacy from Roy's Chapter 4 quote).

73's
Richard Clark, KB7QHC

"Richard Harrison" bravely wrote to "All" (01 Dec 05 14:18:33)
--- on the heady topic of " Antenna reception theory"

RH From: (Richard Harrison)
RH Xref: core-easynews rec.radio.amateur.antenna:220709

RH Roy Lewallen wrote:
RH "You can find the explanation for why this is in any electromagnetic
RH text."

RH I found it in Terman.
[,,,]
RH From the above, it is seen that the electric field is not effective in
RH inducing current in a receiving antenna parallel to a wavefront. All
RH the energy intercepted by the antenna is induced by the magnetic field.


That is outright false. Because I can very easily demonstrate
detecting a static E-field by waving a sensitive probe across it.
An antenna is just a stationary probe with a moving E-field. It is
equivalent. Terman sucks.

A*s*i*m*o*v

.... Horse sense is the result of stable thinking.

Richard,

Terman said no such thing, and your interpretation is clearly in error.

Magnetic fields cannot impart ANY energy to charges, such as electrons
in a wire. This is because the force from a magnetic field on a charge
is always perpendicular to the motion of the charge. No work can be done
by the magnetic field, and the energy of the electrons does not change.
Only electric fields can provide energy to an electron.

Fortunately, Faraday's Law saves the day. Changing magnetic flux is
inextricably intertwined with electromotive force. Terman's comment on
page 2 of the 1955 edition simply points out the operation of Faraday's
Law. (Yes, I have this volume of Terman.)

Your conclusion statement is completely reversed. The magnetic field
does nothing to induce current in the antenna, while the electric field
does everything.

Again, however, the laws of physics save the day. Maxwell's equations
link electric and magnetic fields in such a manner that the magnetic
field you favor creates just enough electric field to drive the
electrons in the wire.

As has been stated many times in this newsgroup, it is not possible to
filter out one field component or the other. As long as there is some
time dependence, i.e., other than purely static fields, both the
electric and magnetic fields coexist.

73,
Gene
W4SZ

Richard Harrison wrote:
Roy Lewallen wrote:
"You can find the explanation for why this is in any electromagnetic
text."

I found it in Terman.

As we all know, we place correctly polarized dipoles, for example,
parallel to the wavefront for maximum response. Terman confirms the
electric field in this instance induces no energy in the antenna. It all
comes from the magnetic field.

If antenna current flows, no matter where it comes from, loss resistance
causes a voltge drop. That`s why the wire needs to be perfect. The
electric field produces no voltage in the antenna because the wavefront
has the same voltage across its entire surface. That`s because it all
left the same point at the same time. So, a wire parallel to the front
has no difference of potential induced by the wavefront`s electric
field. It all must come from the mgnetic field.

On page 2 of his 1955 edition, Terman says:
"The strength of the wave measured in terms of microvolts per meter of
stress in space is also exactly the same voltage that the MAGNETIC FLUX
(my emphasis) of the wave induces in a conductor 1 m long when sweeping
across this conductor with the velocity of light."

From the above, it is seen that the electric field is not effective in
inducing current in a receiving antenna parallel to a wavefront. All the
energy intercepted by the antenna is induced by the magnetic field.

Best regards, Richard Harrison, KB5WZI