Antenna reception theory
 

Asimov wrote:
Yes, but you are changing the topic into static fields. We were
discussing changing electric fields, not statics but dynamics!

When is someone going to come up with a context-free language?
--
73, Cecil http://www.qsl.net/w5dxp

Antenna reception theory
 

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

Antenna reception theory
 

Tom Donaly wrote:
Jim Kelley wrote:

Reg Edwards wrote:

It is impossible for an E-field to exist without an H-field.



Must have been before electrostatics was invented. :-)

ac6xg



How do you make an electrostatic radio wave?
73,
Tom Donaly, KA6RUH

Certainly you're aware that radio waves don't have a monopoly on E
fields, Tom.

73, jk

Antenna reception theory
 

Roy Lewallen wrote:

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.)

Yes, I thought that much was obvious as well.

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

It could be what he was saying. But conductors are are called
conductors for a reason, and it's not necessarily because they conduct
magnetic fields well.

73, ac6xg

Antenna reception theory
 

Jim Kelley wrote:
Certainly you're aware that radio waves don't have a monopoly on E
fields, Tom.

But they should have a monopoly on threads in this newsgroup. :-)
--
73, Cecil http://www.qsl.net/w5dxp

Antenna reception theory
 

Asimov wrote:

"Jim Kelley" bravely wrote to "All" (28 Nov 05 11:52:53)
--- on the heady topic of " Antenna reception theory"

JK From: Jim Kelley
JK Xref: core-easynews rec.radio.amateur.antenna:220506

JK Reg Edwards wrote:

It is impossible for an E-field to exist without an H-field.

JK Must have been before electrostatics was invented. :-)


Yes, but you are changing the topic into static fields. We were
discussing changing electric fields, not statics but dynamics!

But do you agree that it's not impossible for an E field to exist
without an H field?

ac6xg

Antenna reception theory
 

Jim Kelley wrote:
But do you agree that it's not impossible for an E field to exist
without an H field?

Depends upon the context. I suspect he was talking within the
context of RF EM waves? Is it possible for an RF E-field to
exist without an RF H-field?
--
73, Cecil http://www.qsl.net/w5dxp

Antenna reception theory
 

Tom Donaly wrote:
Jim Kelley wrote:

Reg Edwards wrote:

It is impossible for an E-field to exist without an H-field.



Must have been before electrostatics was invented. :-)

ac6xg



How do you make an electrostatic radio wave?


Wave to it first?

- 73 de Mike KB3EIA -

Antenna reception theory
 

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

Antenna reception theory
 

Cecil Moore wrote:

Jim Kelley wrote:

But do you agree that it's not impossible for an E field to exist
without an H field?


Depends upon the context. I suspect he was talking within the
context of RF EM waves?

That's certainly a context where an E field is always accompanied by an
H field. But the statement as it was written is nevertheless untrue.
That was my only point.

Is it possible for an RF E-field to
exist without an RF H-field?

Seems to beg an obvious answer. But the question brings up a point that
people seem to be missing here. An E field is an E field - there are not
different 'kinds' of E fields. The field itself is the same, whether it
varies in time or not. A non-zero dE/dt allows for some of the more
interesting properties to have non-zero solutions, but the fields
themselves are not unique. I hope that concept isn't too controversial
for this group. If it is, I will strive to keep such ideas to myself in
the future.

ac6xg