Antenna reception theory
 

"Cecil Moore" bravely wrote to "All" (30 Nov 05 15:53:50)
--- on the heady topic of " Antenna reception theory"

CM From: Cecil Moore
CM Xref: core-easynews rec.radio.amateur.antenna:220639

I wonder if it is possible to directly measure an E field by the
effect of the virtual quanta in its close vicinity?

CM If the effect of virtual quanta could be measured,
CM would they still be virtual?

Yes, there is a measurable force. The Casimir Effect is the action
virtual particles have on a pair of parallel metal plates, pushing
them together (only by an extremely tiny amount). This is because more
virtual particles are created outside the plates than between them.

A*s*i*m*o*v

.... There are subliminal messages in Campbell's Alphabet Soup!

Antenna reception theory
 

"Jim Kelley" bravely wrote to "All" (30 Nov 05 09:56:52)
--- on the heady topic of " Antenna reception theory"

JK From: Jim Kelley
JK Xref: core-easynews rec.radio.amateur.antenna:220642

JK Asimov wrote:

I think a saturable core can be used to measure a static magnetic
field. Early computer magnetic core memories worked like this.

JK I was referring to the similarity to a rotating coil gaussmeter. I
JK think what you're describing now is something more akin to the
JK fluxgate magnetometer.

Relativity transforms static fields into dynamic fields by adding a
velocity component to the measurement.

JK I see. Is Omni magazine still in print by any chance?

Omni is not my cup of tea. Much too glossy for me!
What I meant was if the person taking the measurement is in motion
relative to the field, then the field will seem to be dynamic.

A*s*i*m*o*v

.... This is an SOS call from the mining ship Red Dwarf

Antenna reception theory
 

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

Antenna reception theory
 

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

Antenna reception theory
 

It looks like time to remind readers that charge isn't the same as
electrons. On a wire, charge moves at nearly the speed of light, while
electrons only go a few miles per hour. Most of the relevant theory
actually deals with the interaction of fields and charge, not fields and
electrons.

Roy Lewallen, W7EL

Antenna reception theory
 

Roy Lewallen wrote:

It looks like time to remind readers that charge isn't the same as
electrons. On a wire, charge moves at nearly the speed of light, while
electrons only go a few miles per hour. Most of the relevant theory
actually deals with the interaction of fields and charge, not fields and
electrons.

Roy Lewallen, W7EL

Good point. Charge can be holes, or electrons, or even ions. It is the
fields which move at the speed of light. Charge tends to have to hang
around with the charge carriers. But once a field arrives someplace, it
will immediately influence the motion of charges that happen to be
hanging around there locally.

ac6xg

Antenna reception theory
 

"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.

Antenna reception theory
 

Asimov wrote:
"Terman sucks."

Termn`s writings have been exposed for anyone to criticize for most of a
century. His 1955 edition has been out there for 50 years. No
retractions or corrections are necessary.

Detection of static E-fields is not relevant.
Charles Coulomb in 1785 showed electric charges exert forces on each
other that are inversely proportional to the square of the distance
between them. This was the birth of the "inverse square law" as
Coulomb`s discovery applies to magnetic attraction and repulsion, too.

In an electromagnetic field, propagation depends upon the electric field
begetting a magnetic field and vice versa. On average, each field
contains 50% of the total energy.

The electromagnetic field of an antenna could be calculated from the
distribution of voltage on the conductors. Problem is voltmeter leads
would be in the r-f field and this would tend to make measured voltages
inaccurate. R-F current is conveniently and accurately measured with a
thermocouple ammeter.

Strength of an electromagnetic wave is usually measured and quoted in
terms of its electric field in volts per meter. This is the number of
volts which would be induced in a one-meter length of wire placed in the
field parallel to the electric lines of force. Volts in the wire are
produced by movement of magnetic flux across the wire.

Best regards, Richard Harrison, KB5WZI

Antenna reception theory
 

Asimov wrote:
"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.

Consider the direction the E field is moving and which direction any
electrostatically induced current might flow. Then apply the same
criteria to a magnetic field.

A*C*6*X*G

Terman sucks.

A*s*i*m*o*v

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

Antenna reception theory
 

"Jim Kelley" bravely wrote to "All" (02 Dec 05 11:17:51)
--- on the heady topic of " Antenna reception theory"

JK From: Jim Kelley
JK Xref: core-easynews rec.radio.amateur.antenna:220745

JK Asimov wrote:
"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.

JK Consider the direction the E field is moving and which direction any
JK electrostatically induced current might flow. Then apply the same
JK criteria to a magnetic field.

JK A*C*6*X*G

JK Terman sucks.

I regret having written that Terman sucks. However, I'm reminded that
there is a lot of stuff missing in the 1955 edition of Encyclopedia
Britanica up in the attic. Clearly I don't say the EB sucks either,
so a 1955 book on electromagentic wave theory might be missing a few
things as well. Unless you believe everything that there ever is to
learn about EM is that 1955 book. But it is wrong to state that the
magnetic field alone is responsible for the interception of wave
energy in a metallic conductor.

A*s*i*m*o*v


.... Isaac Asimov : 1920-1992 : Gone to the stars!