Reg wrote,


Do you have a better idea than a diode probe to sample voltage at the
end of a dipole?

===============================

The only people person who needs to know the volts at the ends of an antenna
conductor such as a 1/2-wave dipole is the antenna designer. He has to
concern himself with insulators, breakdown voltages, the effects of corona
discharge and other such mundane (to other people) things.

Antenna designers, of which extremely few are needed in this small world,
being practical, sensible people who are obliged by professional
self-discipline to keep economy in time and materials foremost in their
minds, do not waste valuable resources researching the 'end-voltage'
question, purchasing latest space-age technology equipment just for a
one-off job, and employing teams of incompetent but highly-paid assistants
and workmen to make one solitary measurement.

Of course they don't !

In a few seconds they just do a little school arithmetic : -

Volts at end of dipole = Q * Vin / 2

Where Vin is centre-fed dipole feedline volts and Q is the dipole's resonant
Q factor.

Q is dipole inductive reactance divided by radiation resistance.

According to the ARRL handbook, Heaviside, Terman, me and countless others,
Q = Omega*L/R

Richard, you are familiar with these elementary notions. Do you not feel a
little saddened, like me, that amateurs, even future professional engineers,
are handicapped by having unnecessarily complicated, incorrect even, ideas
knocked into their heads by do-gooders on this newsgroup, trying to appear
knowledgeable, who should know better ?

I hasten to distinguish between accumulated PRACTICAL EXPERIENCE and
TECHNICAL BAFFLEGAB. The latter is easily recognisable.
===
Reg, G4FGQ


All this post serves to do is confirm the suspicion in many minds, Reg, that
you
haven't ever taken the trouble to study electromagnetics. Might I suggest that,

the next time you read Heaviside's work, you put forth the effort necessary
to understand it. The simple approximations that you rely on so heavily for
your own programs may be good enough for the rough work you demand of them,
but, they are not a statement of reality, and they only work given the narrow
set of
conditions which, for some reason, you always leave unstated.

Tom Donaly, KA6RUH

Dear Tom,

The proof of ANYTHING lies in the EATING.

Your appetite is lacking. As with the one million hoodwinked housewives who
can't be wrong.

Reg.

The point is that there's no "correct" answer. The voltage between two
points separated in space with the presence of a varying magnetic field
can be pretty much anything you'd like it to be -- the value depends, as
others have pointed out, on the path taken between the points. Only Reg
is able to suspend the principles of electromagnetics and confidently
compute a single answer.

Roy Lewallen, W7EL

Richard Harrison wrote:
Roy, W7EL wrote:
"Which orientation would provide the "correct" answer?"

Maybe none.

We know what the correct answer is at the feedpoint. By trial and error
we can find the most stable and least critical placement for our test
lead. We can calibrate our voltage indicator with a sample at the
feedpoint under the conditions that prevail.

A test lead perpendicular to the balanced antenna suffers the least
interference. It`s subject to imperfections and it`s subject to
improvements to overcome the imperfections.

In AM broadcasting we get away with hanging a sampling loop on each
tower of a directional array to monitor both tower current and phase. It
works well enough.

Do you have a better idea than a diode probe to sample voltage at the
end of a dipole?

Best regards, Richard Harrison, KB5WZI

what?
there are multiple answers?
how many?

"Roy Lewallen" wrote in message
...
The point is that there's no "correct" answer. The voltage between two
points separated in space with the presence of a varying magnetic field
can be pretty much anything you'd like it to be -- the value depends, as
others have pointed out, on the path taken between the points. Only Reg
is able to suspend the principles of electromagnetics and confidently
compute a single answer.

Roy Lewallen, W7EL

Richard Harrison wrote:
Roy, W7EL wrote:
"Which orientation would provide the "correct" answer?"

Maybe none.

We know what the correct answer is at the feedpoint. By trial and error
we can find the most stable and least critical placement for our test
lead. We can calibrate our voltage indicator with a sample at the
feedpoint under the conditions that prevail.

A test lead perpendicular to the balanced antenna suffers the least
interference. It`s subject to imperfections and it`s subject to
improvements to overcome the imperfections.

In AM broadcasting we get away with hanging a sampling loop on each
tower of a directional array to monitor both tower current and phase. It
works well enough.

Do you have a better idea than a diode probe to sample voltage at the
end of a dipole?

Best regards, Richard Harrison, KB5WZI

For Reg, only one. For me, an infinite number.

Roy Lewallen, W7EL

H. Adam Stevens wrote:
what?
there are multiple answers?
how many?

"Roy Lewallen" wrote in message
...

The point is that there's no "correct" answer. The voltage between two
points separated in space with the presence of a varying magnetic field
can be pretty much anything you'd like it to be -- the value depends, as
others have pointed out, on the path taken between the points. Only Reg
is able to suspend the principles of electromagnetics and confidently
compute a single answer.

Roy Lewallen, W7EL

In article , Roy Lewallen
wrote:

For Reg, only one. For me, an infinite number.

Roy Lewallen, W7EL

H. Adam Stevens wrote:
what?
there are multiple answers?
how many?

"Roy Lewallen" wrote in message
...

The point is that there's no "correct" answer. The voltage between two
points separated in space with the presence of a varying magnetic field
can be pretty much anything you'd like it to be -- the value depends, as
others have pointed out, on the path taken between the points. Only Reg
is able to suspend the principles of electromagnetics and confidently
compute a single answer.

Roy Lewallen, W7EL

Roy, the good point you are making is often hard to get across. I tried
for about forty years to teach multivariable calculus to EE students and
others. Sometimes I succeeded. But some students couldn't get over the
fact that in one dimension, integrals are independent of the path, and so
they expected that to be true in two dimensions, or in three.

It makes things a lot simpler if you believe that all line integrals are
independent of the path, since from that it follows that integrals around
loops are always zero. That makes things like Green's Theorem and Stokes'
Theorem simpler too, since (if you grant that surface integrals involved
are also zero) they simply say that 0 = 0.

Simple isn't always right. Maybe in some other universe, all fields are
conservative, but not in this one.

David, ex-W8EZE and retired math prof

--
David or Jo Anne Ryeburn

To send e-mail, remove the letter "z" from this address.

David or Jo Anne Ryeburn wrote:
Simple isn't always right. Maybe in some other universe, all fields are
conservative, but not in this one.

It might help if the language was made more understandable. Isn't the
problem in getting an absolute ground reference point at the end of
the dipole? It is possible to model a 3D antenna with a 4th dimension
ground "plane".
--
73, Cecil http://www.qsl.net/w5dxp



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In article , Cecil Moore
wrote:

David or Jo Anne Ryeburn wrote:
Simple isn't always right. Maybe in some other universe, all fields are
conservative, but not in this one.

It might help if the language was made more understandable. Isn't the
problem in getting an absolute ground reference point at the end of
the dipole? It is possible to model a 3D antenna with a 4th dimension
ground "plane".

Nope, that's not the problem. The language I am using is standard. To
understand it, get out your multivariable calculus text, if you've kept
it, or go to the library and borrow a good one. (Shameless plug: Howard
Anton's Calculus book is a good one -- I helped debug it before
publication.) Look up "independence of path" in the section on line
integrals, and look up the related topic of "conservative vector fields".
*That's* the problem, and not anything about ground references. What Roy
is talking about is an important special case of lack of independence of
path; there are many more examples.

David

--
David or Jo Anne Ryeburn

To send e-mail, remove the letter "z" from this address.

No, that's not the problem. The problem is that you're looking for a
single voltage between two points separated in space. There is no single
value for that voltage. If you made some kind of "artificial ground"
close to the antenna, then there are an infinite number of possible
voltages between it and the Earth.

But I'm sure you can work it out as easily with virtual photons and 4
dimensional geometry as Reg does with grade school arithmetic. It's
quite simple, really, if you don't need to have the right answer.

Roy Lewallen, W7EL

Cecil Moore wrote:
David or Jo Anne Ryeburn wrote:

Simple isn't always right. Maybe in some other universe, all fields are
conservative, but not in this one.


It might help if the language was made more understandable. Isn't the
problem in getting an absolute ground reference point at the end of
the dipole? It is possible to model a 3D antenna with a 4th dimension
ground "plane".

Roy Lewallen wrote:
If you made some kind of "artificial ground"
close to the antenna, then there are an infinite number of possible
voltages between it and the Earth.

In four dimensions, the ground is not "artificial" and is
at the same potential as the Earth.
--
73, Cecil http://www.qsl.net/w5dxp



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