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-   -   Voltage/Current at the end of a dipole? (https://www.radiobanter.com/antenna/589-voltage-current-end-dipole.html)

Roy Lewallen October 17th 03 10:16 PM

How 'bout you model it with your concept of an "artificial ground", and
let us know the result? You can measure the voltage with EZNEC by
connecting the two points to be measured with a wire and inserting a
zero amplitude current source in the wire. The source will act like an
open circuit, and the voltage will be reported in the Source Data output.

After you've determined the voltage relative to your "artificial
ground", modify the "artificial ground" and note the effect on the
voltage. Then see if you can figure out what the voltage is between the
"artificial ground" and the Earth. Or, give us your justification for
assuming that it's zero. If it is zero, via what path? As Tom has been
saying, the voltage between two points depends on the path you take
between them.

Roy Lewallen, W7EL

Cecil Moore wrote:
Ian White, G3SEK wrote:

In practice that will means that the voltage you measure between say
the end of a whip and ground will depend on how you choose to route
the connecting leads to the voltmeter, and how you connect to
ground... and above (below?) all on what you define "ground" to be.



How about using an artificial ground at the measurement point?
--
73, Cecil, W5DXP



Cecil Moore October 17th 03 10:19 PM

Roy Lewallen wrote:
After you've determined the voltage relative to your "artificial
ground", modify the "artificial ground" and note the effect on the
voltage. Then see if you can figure out what the voltage is between the
"artificial ground" and the Earth. Or, give us your justification for
assuming that it's zero. If it is zero, via what path? As Tom has been
saying, the voltage between two points depends on the path you take
between them.


Wow, you sure ASSume a lot from a simple question. Let's turn it around
and you guys prove that the voltage at the ends of a dipole is less
than or equal to the feedpoint voltage even though a florescent light
bulb is brighter at the ends.
--
73, Cecil http://www.qsl.net/w5dxp



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Tdonaly October 17th 03 11:40 PM

Cecil wrote,

Wow, you sure ASSume a lot from a simple question. Let's turn it around
and you guys prove that the voltage at the ends of a dipole is less
than or equal to the feedpoint voltage even though a florescent light
bulb is brighter at the ends.
--
73, Cecil http://www.qsl.net/w5dxp


What causes the light to light up, Cecil, an E field, or a V field?
You can't seem to get over the fact that the voltage between
two points in a time varying E field may not be unique and thus
not measurable. Go read the book I told you to read, Cecil,
and you'll understand why.
73,
Tom Donaly, KA6RUH



Tom Bruhns October 18th 03 12:31 AM

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

Cecil Moore October 18th 03 05:52 AM

Tdonaly wrote:
Cecil wrote,
Bend the ends of a resonant dipole around close to each other and
measure the voltage with a shielded differential RF voltmeter. For
100 watts input, you will get almost 1000 volts RMS between the ends,
a far cry from the ~70 volts RMS at the center feedpoint.


You missed the point, again, Cecil. Carry on.


Nope, you missed the point. This ain't rocket science.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore October 18th 03 05:55 AM

Tdonaly wrote:
What causes the light to light up, Cecil, an E field, or a V field?
You can't seem to get over the fact that the voltage between
two points in a time varying E field may not be unique and thus
not measurable. Go read the book I told you to read, Cecil,
and you'll understand why.


Why not just tell me to read the Bible where God is the cause
of everything - same difference.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore October 18th 03 06:05 AM

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 Moore October 18th 03 06:58 AM

Tdonaly wrote:
What causes the light to light up, Cecil, an E field, or a V field?


According to quantum electrodynamics, fields don't exist. So are
you talking about photons or virtual photons above? In either case,
voltage can still be measured by a voltmeter.
--
73, Cecil http://www.qsl.net/w5dxp



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Tdonaly October 18th 03 07:36 AM

Cecil wrote,

Why not just tell me to read the Bible where God is the cause
of everything - same difference.
--
73, Cecil http://www.qsl.net/w5dxp


That's about the kind of reply I expected, which is too bad.
It sort of reminds me of the Catholic clerics who refused to
look through Galileo's telescope.
73,
Tom Donaly, KA6RUH



Tdonaly October 18th 03 07:54 AM

Cecil wrote,

Tdonaly wrote:
What causes the light to light up, Cecil, an E field, or a V field?


According to quantum electrodynamics, fields don't exist. So are
you talking about photons or virtual photons above? In either case,
voltage can still be measured by a voltmeter.
--
73, Cecil http://www.qsl.net/w5dxp


I see you've gone into objection-stopper mode: write something
whether it makes sense or not. Evidently, you don't know what
makes the little light light up, or you'd answer the question.
73,
Tom Donaly, KA6RUH






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