Michael Black wrote:
art ) writes:

Pat Hawker was the only part that I read but lately he seems to be
rambling.


I'm rather surprised that he's still doing the column. It's been
thirty years since I bought a collection of Technical Topics, and later
I found a used one dating from the sixties. I have no idea when
he started doing it (wait, I guess if this is "50 years of antenna topics"
then it must be fifty years), but I suspect nobody has had such a long
running column in the ham magazines.

Of course, such columns are relatively easy to write, since it's a filtering
of a lot of material down to it's essence.



Actually, such columns can be very difficult to write. Distilling to
the essence, without losing an essential detail, can be quite
challenging. Anyone can write a 200 page tome that covers something in
all its gory detail, given sufficient time and effort. It's
substantially harder to make an adequate summary in 100 words, and doing
it on a deadline.

Sort of like writing meaningful abstracts for a technical paper.

"Cecil Moore" wrote
The characteristic impedance of a horizontal dipole is
~constant. Since a dipole is a standing wave antenna,
the voltage to current ratio varies along its length.
That varying impedance (V/I) is NOT the characteristic
impedance which is relatively constant for a horizontal
wire.
--
73, Cecil http://www.w5dxp.com


Cecil,
How do we apply (calculate char. imp.) the above to say, full wave (quad)
loop or vertical monopole?

Yuri, K3BU

Cecil Moore wrote:
Tom Donaly wrote:
Cecil Moore wrote:
The characteristic
impedance of a horizontal wire above ground is
constant at 138*log(4D/d)

The characteristic impedance is not to be confused
with the voltage to current ratio existing on a
standing-wave antenna any more than the characteristic
impedance of a transmission line is to be confused
with the voltage to current radio existing along
its length when the SWR is not 1:1.

Have you verified this experimentally, Cecil? If you did,
how did you do it?

Here's a quote from "Antennas Theory" by Balanis: "The current
and voltage distributions on open-ended wire antennas are similar
to the standing wave patterns on open-ended transmission lines.
... Standing wave antennas, such as the dipole, can be analyzed
as traveling wave antennas with waves propagating in opposite
directions (forward and backward) and represented by traveling
wave currents If and Ib ..."

As Balanis suggests, the body of technical knowledge
available for "open-ended transmission lines" is applicable
to "open-ended wire antennas", e.g. dipoles, which really
are nothing but lossy *single-wire* transmission lines.

That characteristic impedance equation for a single-wire
transmission lines can be found in numerous publications and
is close to a purely resistive value. A #14 horizontal wire
30 feet above ground is very close to a characteristic
impedance of 600 ohms. (One half of a 1/2 wavelength dipole
is simply a lossy 1/4 wavelength stub with Z0 = ~600 ohms.)

Before he passed, Reg Edwards had some earlier comments on
the characteristic impedance of a 1/2WL dipole above ground.

Like a normal transmission line open stub, a 1/2WL
dipole supports standing waves that can be analyzed. For the
purposes of a voltage and current analysis, I^2*R losses and
radiation losses can be lumped together into total losses
associated with some attenuation factor, similar to analyzing
a 1/4WL lossy normal stub.

In fact, the losses to radiation from
one half of a 1/2WL dipole can be simulated by EZNEC using
resistance wire in a 1/4WL open stub. Using EZNEC with a
resistivity of 2.3 uohm/m for a 1/4WL open stub gives a pretty
good model of what is happening with one half of a 1/2WL dipole
which is only a lossy single-wire transmission line above earth.

So you haven't verified it experimentally, and don't know how
to do so. Thanks for the answer.
73,
Tom Donaly, KA6RUH

Yuri Blanarovich wrote:
"Cecil Moore" wrote
The characteristic impedance of a horizontal dipole is
~constant. Since a dipole is a standing wave antenna,
the voltage to current ratio varies along its length.
That varying impedance (V/I) is NOT the characteristic
impedance which is relatively constant for a horizontal
wire.

How do we apply (calculate char. imp.) the above to say, full wave (quad)
loop or vertical monopole?

That's a good question. For a horizontal wire, its obvious
that the forward wave reflects from the open-circuit at the
end of the wire. We know there are standing waves on a loop
but exactly where are the reflections originating? I
suspect they are originating at the feedpoint, i.e. the
forward wave travels all the way around the loop and is
reflected from the impedance discontinuity at the feedpoint.
Note that the feedpoint impedance of a full-wave loop is
in between the feedpoint impedances of a 1/2WL dipole and
a 1.5WL dipole indicating that the forward wave travels
about 1WL before being reflected in the loop.

Every segment of a monopole is a different
distance from ground and therefore has a slightly different
characteristic impedance which probably doesn't change very
fast as it is a log function. For instance, for the sake
of discussions, it seems reasonable to assume that the Z0
of a vertical stinger is in the neighborhood of a few
hundred ohms and would be easy to measure. At whatever
frequency causes the stinger to be 1/8WL, measure the
impedance. That will be fairly close to the characteristic
impedance of the stinger at the measurement point.
--
73, Cecil http://www.w5dxp.com

Tom Donaly wrote:
Cecil Moore wrote:
Here's a quote from "Antennas Theory" by Balanis: "The current
and voltage distributions on open-ended wire antennas are similar
to the standing wave patterns on open-ended transmission lines.
... Standing wave antennas, such as the dipole, can be analyzed
as traveling wave antennas with waves propagating in opposite
directions (forward and backward) and represented by traveling
wave currents If and Ib ..."

So you haven't verified it experimentally, and don't know how
to do so. Thanks for the answer.

Do you distrust the theory of relatively because you
haven't verified it experimentally and don't know
how to do so?

I have simulated the configuration using EZNEC.

Tom, like you, I trust the great engineers and physicists
who came before me. I do not develop every concept from
first principles. If an analysis suggested by Balanis is
not good enough for you, that's your choice. Incidentally,
Kraus says essentially the same thing as Balanis about
analyzing standing-wave antennas.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
At whatever
frequency causes the stinger to be 1/8WL, measure the
impedance. That will be fairly close to the characteristic
impedance of the stinger at the measurement point.

As a data point, using EZNEC's VERT1.EZ 40m vertical,
the feedpoint impedance at 3.6 MHz is 6 - j356 ohms.
That would make the Z0 at the feedpoint around 360
ohms and Z0 no doubt increases with distance above
ground.
--
73, Cecil http://www.w5dxp.com

Mike
I hope you learn from your exchange with Richard.
His only interest is not to aid in your thoughts but to take a
swipe at you after every paragraph. He is trying to taunt you.
He will also intimate, but without saying so, that he has all
the answers to your quandry as a way of enticing you for a longer
dialogue which for him are far and few between on this newsgroup.
Obviously you can now see why.
I have been informed that he has responded to the "skin" thread.
I have not read it nor will I reply to it, since I know before hand it
will contain nothing but taunts either to me or the prior poster.
The best thing for Richard's posts is if you must read them then smile
at his childish actions and then move on. Either way, from now on
he is going to take a swipe at you at every opportunity to provoke
you into a dialogue with him where the scenario will repeat itself
all over again.
Tolerate him but without engagement.
Best Regards
Art Unwin.....KB9MZ....xg

Richard Clark wrote:
On Thu, 15 Nov 2007 12:29:08 -0000, "Mike Kaliski"
wrote:

Thanks for yor comments and encouragement. I can well understand your
skepticism and accept that this idea is pretty far out. As you rightly point
out, there are a whole host of issues revolving around what is being
defined, measurement methods and interpretation of results.

Hi Mike,

OK, but this still tells me nothing of what issue you think I am
skeptical about!

The small transmitting loop efficiency experiments were carried out using
thermographic imaging to try and identify areas of heating within the loops.

Good, that is instructive.

The areas with maximum heating would indicate high current flow or high
resistance.

More properly, their product - Watts.

This information was used to try and derive a theory of
operation and efficiency figures for the loops. The idea being to prove that
efficiency was in fact higher than predicted by the Chu theory.

This names only one theory and doesn't actually illustrate any
differences.

The
methodology and results of the experiment were challenged and Chu theory
seems to have won out, at least for the time being.

Again, all of this is suggestive, not informative. Returning to your
earlier complaint of "detailed research" we have no details beyond
heat imaging challenging the establishment.

I don't see that there would be any need to invoke non standard units for
experimental measurements, ohms, amps and volts should suffice.

Too often, this group has to wade through "what it is not" instead of
"what it is." Tell us what specific units would be convincing for
you, as you have introduced a complaint that needs to be satisfied.

I have not
worked out the best measurement methods or instrumentation to use, but I am
sure that existing equipment and techniques will suffice.

I have worked on a world of instruments (more than anyone here).
Believe me, that experience has NOT answered the question of the ages.

Small sampling
coils, hall effect devices, temperature measurement
probes and thermal cameras are all available at prices which an amateur
experimenter can afford, so there is no reason why these experiments could
not be carried out in a domestic environment rather then an industrial one.

OK, by induction, I presume you are harkening back to these thermal
maps or imaging.

Well, in fact they have been done, their results have been posted to
the net and argued here. You didn't get the invitation?

Unfortunately, that contributor was arguing smaller loops, coils
specifically and the mapping was tangential to the rant. He promised
more data when Spring weather would allow him to pursue this line of
inquiry, but that was several Springs ago, and he has in the interval
chosen to -um- till the same ground.

The reason for specifying a single radiating element is because directional
and reflecting elements absorb and re-radiate RF energy. Once the properties
of a single element are known, then it is possible to add additional
elements and make further measurements and assessments of performance. Since
it is already known that all the elements of an antenna interact with one
another, it is important to start with the basics and work up from there.

True, and certainly it stands to improve clarity by reducing
variables.

The choice of the word 'within' was unfortunate because I accept that there
is nothing going on actually within an antenna element, skin effect ensuring
that RF travels on the outside of conductors.

Plus, thermal imaging would be hard pressed to peer inside a
conductor.

So I come back to my assertion that very little detail seems to have been
published about what is happening really close in to antennas i.e. on the
actual elements making up the antenna. Loads of stuff about near field and
far field experiments, but not specific points of radiation from the antenna
elements. It may all be a complete waste of time but at least I will have
fun and hopefully learn some new stuff doing it.

You mean you are unfamiliar with this work. I've posted my own here
to little attention, I don't think this cycle will attract much more,
but here it is:
http://home.comcast.net/~kb7qhc/ante...pole/index.htm

This doesn't actually attend your preference of thermal mapping, but
you are still vague to the point of "what is happening really close in
to antennas" (even qualified by "on the actual elements" - there's
that word actual again which lends nothing to a specification).

There is an entire field of Science devoted to this (beyond the scope
of many here who would anticipate my answer being "Fields"). This
field is called Plasmonics. Books are written about it, pictures are
taken of it, and I've sat through hours of presentations demonstrating
it. Unfortunately, this crowd of investigators, like Arthur, have
re-invented the wheel and they proclaim it is square.

The long and short of it is that you stand to become more confused,
but it could be rewarding if you wear asbestos.

73's
Richard Clark, KB7QHC

On Thu, 15 Nov 2007 12:27:52 -0800 (PST), art
wrote:

I hope you learn from your exchange with Richard.

Hi Arthur,

Thanx for the flowers!

73's
Richard Clark, KB7QHC

Cecil, W5DXP wrote:
"I suapect they (reflections) are originating at the feedpoint, i.e. the
forward wave travels all the way around the loop and is reflected from
the impedance discontinuity at the feedpoint."

That would be a reflection from a virtual impedance bump wouldn`t it?

The wave travels both wires of a feedline simultaneously, and enters
both ends of the loop at the same time. The collision is at the midpoint
of the loop opposite the feedpoint.

Arnold B. Bailey says on page 399 of "TV and Other Receiving Antennas":
"Now, in the loop, the far-end reflection point is a short circuit, and
hence, the current is high at this far end."

Best regards, Richard Harrison, KB5WZI

Cecil Moore wrote:
Tom Donaly wrote:
Cecil Moore wrote:
Here's a quote from "Antennas Theory" by Balanis: "The current
and voltage distributions on open-ended wire antennas are similar
to the standing wave patterns on open-ended transmission lines.
... Standing wave antennas, such as the dipole, can be analyzed
as traveling wave antennas with waves propagating in opposite
directions (forward and backward) and represented by traveling
wave currents If and Ib ..."

So you haven't verified it experimentally, and don't know how
to do so. Thanks for the answer.

Do you distrust the theory of relatively because you
haven't verified it experimentally and don't know
how to do so?

I have simulated the configuration using EZNEC.

Tom, like you, I trust the great engineers and physicists
who came before me. I do not develop every concept from
first principles. If an analysis suggested by Balanis is
not good enough for you, that's your choice. Incidentally,
Kraus says essentially the same thing as Balanis about
analyzing standing-wave antennas.

I actually do know how to verify Einstein's predictions because the
fellows who did it wrote detailed articles on how they did it.

Thinking of antennas as transmission lines is an old practice. It
doesn't mean it's very practical, or that it hasn't been superseded
by a better analogy. For that matter, a vibrating guitar string can
be analyzed as a transmission line, as can any woodwind instrument.
That doesn't mean it's worth doing, but it can be done. The problem is
when a gentleman, such as the late, lamented Reg Edwards, or the still
kicking, unlamented you, write that an antenna, or a clarinet _is_ a
transmission line.
73,
Tom Donaly, KA6RUH