Tom Bruhns wrote:
If you tell me
there is a large voltage along a good conductor, then I know there is
a very large heat dissipation in that wire.

There are large voltages along my open-wire feedline when
the SWR is high, but very low heat dissipation in that wire.
Hint: think standing waves on the antenna wire.
--
73, Cecil, W5DXP

Cecil Moore wrote in message ...
Tom Bruhns wrote:
If you tell me
there is a large voltage along a good conductor, then I know there is
a very large heat dissipation in that wire.

There are large voltages along my open-wire feedline when
the SWR is high, but very low heat dissipation in that wire.
Hint: think standing waves on the antenna wire.

It's TEM line, right? The voltages are practically all ACROSS the
line, between the conductors. There is very little voltage ALONG the
conductors, just I*R (and note the directions for _that_). Go look up
Faraday's Law of Magnetic Induction, and refresh your understanding of
Kirchoff's Voltage Law and Ohm's Law as well. Those three pretty much
let you figure it all out.

Cheers,
Tom

Tom Bruhns wrote:
There is very little voltage ALONG the conductors, ...

Depends upon how long the conductors are. The difference along a
1/4WL conductor is known to be minimum VS maximum assuming a
minimum at one end. Are you saying that EZNEC doesn't display
the current distribution on an antenna when I press the 'i' key?
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil, I'm sorry you don't understand that in the presence of
time-varying fields, the potential between two points depends on the
path you take. Grasping that concept can be very empowering in
understanding what's going on in antennas, and in transmission lines,
and in inductors and transformers. I can only hope that some lurkers
have benefitted from the discussion.

Cheers,
Tom

Cecil Moore wrote in message ...
Tom Bruhns wrote:
There is very little voltage ALONG the conductors, ...

Depends upon how long the conductors are. The difference along a
1/4WL conductor is known to be minimum VS maximum assuming a
minimum at one end. Are you saying that EZNEC doesn't display
the current distribution on an antenna when I press the 'i' key?

Tom Bruhns wrote:
Cecil, I'm sorry you don't understand that in the presence of
time-varying fields, the potential between two points depends on the
path you take.

I know that, Tom, but we are talking about measuring the RF voltage
between two copper wires one inch apart. The path is well defined.
It is a no brainer. There is no need for obfuscation. The measurement
proves the voltages at the ends of a dipole to be at least a magnitude
higher than the voltage at the feedpoint. Are you not aware of how
the ratio of voltage to current varies over 1/4WL of a wire antenna?
--
73, Cecil http://www.qsl.net/w5dxp



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Tom Bruhns wrote:
Cecil, I'm sorry you don't understand that in the presence of
time-varying fields, the potential between two points depends on the
path you take.

I know that, Tom, but we are talking about measuring the RF voltage
between two copper wires one inch apart. The path is well defined.

That's one path.

It is a no brainer. There is no need for obfuscation.

Universally recognized principles of electromagnetics are obfuscation?

The measurement
proves the voltages at the ends of a dipole to be at least a magnitude
higher than the voltage at the feedpoint.

You changed the geometry. But even if you hadn't, you might be
able to say the changing electrical fields are greater at the ends of
a dipole, but not the voltages, because the voltages
aren't uniquely defined.

Are you not aware of how
the ratio of voltage to current varies over 1/4WL of a wire antenna
--
73, Cecil http://www.qsl.net/w5dxp


There's not much point in arguing with you Cecil, since you don't want
to countenance the more sophisticated ideas of some of the other
posters to explain what's going on at the ends of a dipole. That's
too bad. You'll give some people the impression that things are
as simple as you say they are when things are not simple
at all. If they were, even an old hick like me could become an
engineer, and the job wouldn't pay much at all.
73,
Tom Donaly, KA6RUH

Tdonaly wrote:
Universally recognized principles of electromagnetics are obfuscation?

Complicating a simple measurement task beyond belief is obfuscation.

You changed the geometry. But even if you hadn't, you might be
able to say the changing electrical fields are greater at the ends of
a dipole, but not the voltages, because the voltages
aren't uniquely defined.

When a dipole is bent into an open loop, the relative voltage between
the ends is uniquely defined just like the voltage across a transmission
line is uniquely defined. If I poke two wires through two holes in a
faraday cage and ask you to measure the 10 MHz voltage between them
with 10% accuracy, would you say it can't be done?

You'll give some people the impression that things are
as simple as you say they are when things are not simple
at all.

The measurement may be extremely challenging, but the *concepts* are simple.
All you need to do is note the similarity of the transmission line impedances
on an SWR circle to a wire antenna. If the spacing on a transmission line is
an appreciable percentage of a wavelength, the transmission line will radiate.
That's all a center-fed wire antenna is - a transmission line with large
spacing between the conductors and it radiates.
--
73, Cecil http://www.qsl.net/w5dxp



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