Cecil,

Sorry, I mistakenly thought the discussion was about technology.
Silly me!

Since it is actually about psychology, not physics, I am outta here.

73,
Gene
W4SZ

Cecil Moore wrote:

You don't even know me, Gene. Where do you get the balls to
decide what I need to worry about and what I don't need to
worry about? I have been worried and needing an energy analysis
model for 40 years. I now have one and can now sleep like a baby
at night, but no thanks to you. :-)

Gene Fuller wrote:
Sorry, I mistakenly thought the discussion was about technology.
Silly me!

We wouldn't have technology without the human need and
drive to understand nature. Many great scientists were
textbook examples of O-C personalities.
--
73, Cecil http://www.qsl.net/w5dxp

Roy Lewallen, W7EL wrote:
"A short while ago, I explained why your Faraday cage doesn`t separate E
and H as you claim."

There are many examples of Faraday screens at work removing the E field
while allowing H field coupling. I chose the Faraday sdreens in medium
wave broadcasting used to reduce radiation of harmonics of the channel
frequency.

More numerous examples abound. These are the Faraday screens used in
isolation power transformers between primary and secindary coils to
prevent transient high-frequency energy coupling.

My 19th edition of the ARRL Antenna Book contains yet another example on
page 14-2 which says:
"Fig 2 - Shielded loop for direction finding.
The ends of the shielding turn are not connected, to prevent shielding
the loop from magnetic fields. The shield is effective against electric
fields.

Best regards, Richard Harrison, KB5WZI

Roy, W7EL wrote:
"If the wavelength is 1m, the voltage induced in the center of an
open-circuited 1m dipole by a 1V/m field is 0.5 volt, not 1 volt."

An open-circuited dipole (has a small gap in its middle) is mot
resonnant at a wavelength of 2 meters, but its individual pieces are
resonant at a wavelength of 1 meter. At 2 meters, not a wavelength
1m, each 0.5 m piece of the half-wavelength, 1 meter long dipole has a
high reactance because 0.5 m is too short at a wavelength of 2 meters
to be resonant. At longer wavelengths, the reactance rises.. High
reactance does not oppose non-existing current in an open-circuit.

I agree the voltage induced in 1/2-meter of wire properly placed within
a 1V/m uniform field is 0.5 volt, not 1 volt. The induced voltage in a
wire within a uniform field sweeping the wire rises uniformly along the
wire. It can be assumed to be the summation of tiny increments of
voltage all along the wire. The voltages of the too-short dipole halves
add just as two cells in some flashlights add. Their vectors are head to
tail. But, current will be limited by radiation and loss resistances of
the wires. It will also be limited by reactance in the wires.
Open-circuit, 0.5 V + 0.5 V = 1V.

Best regards, Richard Harrison, KB5WZI

Richard (Harrison),

What is the voltage measured between the bottom end and ground, of a 1
metre high vertical antenna, above a perfect ground, when the
vertically-polarised field strength is 1 volt per metre, and antenna
height is shorter than a 1/4-wavelength.

Just a number please.
----
Reg.

Reg, G4FGQ wrote:
"What is the voltage measured between the bottom end and ground of a 1
metre high vertical antenna above a perfect ground when the
verticallly-polarized field strength is 1 volt per metre, and antenna
height is shorter than a 1/4-wavelength?"

I see no tricks in the question. The field strength is given as "1 volt
per metre".

From page 23-3 of the 19th edition of the ARRL Antenna Book:
"The standard of measure for field intensities is the voltage developed
in a wire that is 1 meter long, expressed as volts per meter."

While field strength is not the same as the volts delivered to a
receiver, because of the voltage division between antenna impedance and
receiver input impedance, there is no voltage division when the antenna
is loaded with an open circuit. We assume the r-f voltmeter used to
measure voltage at the base of the antenna has an infinite input
impedance. The antenna used for field strength measurements is often a
loop, but we are not concerned with the measurement itself. Reg had a
very simple question, "What`s the voltage at the base of a 1-meter high
wire?

The voltage at the base of an open-circuit 1-metre wire iis one volt
because it goes straight to the definition of field intensity in
volts/m.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
. . .
I agree the voltage induced in 1/2-meter of wire properly placed within
a 1V/m uniform field is 0.5 volt, not 1 volt. The induced voltage in a
wire within a uniform field sweeping the wire rises uniformly along the
wire. It can be assumed to be the summation of tiny increments of
voltage all along the wire. The voltages of the too-short dipole halves
add just as two cells in some flashlights add. Their vectors are head to
tail. But, current will be limited by radiation and loss resistances of
the wires. It will also be limited by reactance in the wires.
Open-circuit, 0.5 V + 0.5 V = 1V.

There are two incorrect statements here.

First, the voltage induced in the wire doesn't rise uniformly along the
wire. It's sinusoidal, even for a very short wire. This is different
from the transmitting case but interestingly doesn't interfere with
reciprocity.

Secondly, the voltage at the center of an open-circuited 1 meter
(electrically short) dipole in and parallel a 1 volt/meter field is 0.5
volt as I said earlier, not 1 volt.

I'll be glad to provide a number of references. Both these statements
can also be verified by modeling.

The definition of field strength, incidentally, has nothing to do with
the voltage of a dipole immersed in that field.

Roy Lewallen, W7EL

Richard Harrison wrote:
. . .
The voltage at the base of an open-circuit 1-metre wire iis one volt
because it goes straight to the definition of field intensity in
volts/m.

Do you have a reference which defines field strength in terms of voltage
induced in a wire?

Roy Lewallen, W7EL

Roy Lewallen wrote"
"Do you have a reference which defines field strength in terms of
voltage induced in a wire?"

Here is more of one I already posted. It is from the 19th edition of the
ARRL Antenna Book on page 23-3:
"The strength of a wave is measured as the voltage between two points
lying on an electric line of force in the plane of the wave front. The
standard of measure for field intensity is the voltage developed in a
wire that is 1 meter long, expressed as volts per meter. (If the wire
were 2 meters long, the voltage developed would be divided by two to
determine the field strength in volts per meter.)"

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Roy Lewallen wrote"
"Do you have a reference which defines field strength in terms of
voltage induced in a wire?"

Here is more of one I already posted. It is from the 19th edition of the
ARRL Antenna Book on page 23-3:
"The strength of a wave is measured as the voltage between two points
lying on an electric line of force in the plane of the wave front. The
standard of measure for field intensity is the voltage developed in a
wire that is 1 meter long, expressed as volts per meter. (If the wire
were 2 meters long, the voltage developed would be divided by two to
determine the field strength in volts per meter.)"

Best regards, Richard Harrison, KB5WZI


Thanks. I'll contact Dean Straw to get that corrected.

Roy Lewallen, W7EL