On Fri, 05 Nov 2004 19:15:01 GMT, Gene Fuller
wrote:

Richard,

It is not clear just what you were trying to demonstrate, but there was
no obvious connection to Rr. Maximum gain is unrelated to Rr.

Hi Gene,

The tenor of correspondence here would suggest otherwise. The
evidence of testing would suggest there is. The disconnect is that
the evidence counters the suggestions in correspondence.

Were you looking for validation that you correctly loaded the numbers
into EZNEC?

Looked OK to me.

Thanx, but now we may BOTH be wrong. ;-)

For short antennas this reference point is generally taken as the
feedpoint, which is also the current maximum point. There is no loss

I did explicitly state that wire loss had been turned on, and real
ground was used.

, so
all power into the antenna is radiated. Therefore the Rr for each of
your perfect world

Again, there was no "perfect world."

, zero loss examples is proportional to the feedpoint
resistance. Apply an appropriate scaling factor (a) if you want the
correct numbers.

Wholly unnecessary, EZNEC can cope with loss quite well and
demonstrates a real world solution (barring my errors of commission or
omission) within tolerable limits.

Did you have a question about something?

I would appreciate other effort in kind to correct any oversights
I've made

The bottom line, of course, is that none of this matters in a perfect
world with zero loss. All the power input is shot into space. Please let
us know where we can find that perfect world :-)

You are right about your quality of trolling. A "perfect world?" You
couldn't supply one? ;-)

73's
Richard Clark, KB7QHC

On Fri, 05 Nov 2004 10:45:57 -0800, Jim Kelley
wrote:

I have a question. Can you express the mathematical and/or physical
relationship between Rr and antenna gain? It would sure help to clarify
the point you were trying to make.

Hi Jim,

I would have thought someone else could, given the bandwidth of
discussion in making the current taper shorter and the constant
current section longer. Testing does not bear their facile
relationship out however, and for the topic of a short antenna
(otherwise, why are we talking about loading coils?) it would seem
that antenna gain is immutable over several octaves below a
quarterwave length.

Of course, I coulda done something wrong. I did use a commonly
available design. I did use a commonly available modeler. I even may
have done the wrong thing in choosing a design that could be evaluated
for free. Perhaps I erred in providing the cogent details of
construction. It took all of 20 minutes to accomplish (far less time
than that expended in theories of current-in/current-out). These
technical hurdles appear to have set the bar too high for my work's
refutation in kind. I appreciate that "it's hard work!" ;-)

To answer your question, if you just abandon the perfect load, then
you stand to achieve a higher gain. If you shorten the antenna, then
you stand to achieve a higher gain. There is no change in Rr with the
addition of Xl. Hence the mathematical relationship for an antenna
shorter than quarterwave would be suggested as:
gain ~ 1/Rr
gain ~ 1/Xl
Rr Z

Don't take this gain to the bank however.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
Cecil Moore wrote:
Kraus and Balanis also express the same ideas

:-)

Apparently, you are not reading the quotes: From "Antennas For All
Applications", by Kraus and Marhefka, 3rd edition:

From page 187 regarding standing wave ANTENNAS:
"A sinusoidal current distribution may be regarded as the standing
wave produced by two uniform (unattenuated) traveling waves of equal
amplitude moving in opposite directions along the antenna."

From page 465 regarding a dipole ANTENNA longer than 1/2WL:
"When the antenna (dipole) is infinitesimally thin, the phase varies
as a step function, being constant over 1/2WL and changing by 180 deg.
at the end of the 1/2WL interval. This type of phase variation is observed
in a PURE STANDING WAVE." emphasis mine.

****************

From _Antenna_Theory_, Balanis, Second Edition, Chapter 10, page 488 & 489
"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 ..."

I got my ideas from Kraus and Balanis, and in particular from Balanis'
antenna courses at ASU where he found no fault with my ideas.

Do you agree or disagree with Kraus and Balanis that standing wave antennas
exhibit standing waves? If they do, they follow the well known laws of physics
governing standing waves.

The combined effort to suppers the ideas of Kraus and Balanis is getting more
ridiculous with each passing day. It can no longer be explained by ignorance.
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil Moore wrote:
The combined effort to suppers the ideas of Kraus and Balanis is getting

Darn spellchecker. "suppers" should be "suppress".

more ridiculous with each passing day. It can no longer be explained by
ignorance.
--
73, Cecil http://www.qsl.net/w5dxp


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Gene Fuller wrote:
The bottom line, of course, is that none of this matters in a perfect
world with zero loss. All the power input is shot into space. Please let
us know where we can find that perfect world :-)

EZNEC? - lossless antennas and ground planes.
--
73, Cecil http://www.qsl.net/w5dxp


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On Fri, 05 Nov 2004 13:57:16 -0600, Cecil Moore
wrote:
The combined effort to suppers the ideas of Kraus and Balanis is getting
Darn spellchecker. "suppers" should be "suppress".
more ridiculous with each passing day. It can no longer be explained by
ignorance.
Blame the spellchecker?

Richard Clark wrote:

First I will start with a conventionally sized quarterwave and by
iteration approach the short antenna and observe effects. I am using
the model VERT1.EZ that is in the EZNEC distribution and modifying it
by turns. For instance, I immediately turn on the wire loss.

40mm thick radiator 10.3 meters tall:
Impedance = 36.68 + J 2.999 ohms
which lends every appearance to expectation of Rr that could be
expected from a lossless perfect grounded world.
Best gain is
-0.03dBi

next iteration:

cut that sucker in half:
Impedance = 6.867 - J 301 ohms
which, again, conforms to most authorities on the basis of Rr.
best gain
0.16dBi
How about that! More gain than for the quarterwave (but hardly
remarkable).

This is indeed an interesting result, even though it's small. As a
dipole or monopole gets shorter than a resonant length, the current
distribution changes from sinusoidal to triangular. In the ideal case
(and in the absence of loss), this results in the shorter antenna having
a slightly fatter pattern and therefore slightly less gain. An
infinitesimally short antenna has a gain of less than 0.5 below that of
a resonant one, due to this (and again, in the absence of loss). So the
trend you observed was backwards. The first two things I checked --
segmentation and wire loss -- proved to not be the reason. It appears to
be the effect of the current distribution on the reflected wave from the
ground. The radiation from each part of the antenna reflects from the
ground, and the nature of the reflection depends on the angle at which
it strikes the ground. Radiation from different parts of the antenna
strike at different angles, and the shorter antenna has its current,
therefore its radiation, apportioned differently. It's this difference
that causes the slight backward trend in gain. I wouldn't put too much
weight on it, however, both because of its being small, and that EZNEC
and similar programs use a pretty simple ray-tracing method of
calculating ground reflection rather than a more complex method which
includes diffraction and other effects. You'll see the theoretical trend
if you change the ground type to Perfect, and likely a slightly
different trend if you change the ground constants.

This makes me wonder why any futzing is required except
for the tender requirements of the SWR fearing transmitter (which, by
the way, could be as easily taken care of with a tuner).

next iteration:

load that sucker for grins and giggles:
load = 605 Ohms Xl up 55%
Impedance = 13.43 + J 0.1587 ohms
Did I double Rr? (Only my hairdresser knows.)
best gain
0.13dBi
Hmm, losing ground for our effort, it makes a pretty picture of
current distribution that conforms to all the descriptions here (sans
the balderdash of curve fitting to a sine wave). I am sure someone
will rescue this situation from my ineptitude by a better load
placement, so I will leave that unfinished work to the adept
practitioners.

As I pointed out above, going from a sinusoidal to a triangular
distribution changes the gain less than 0.5 dB, so this change in
distribution changes the gain even less. And again, the interaction with
real ground reverses the trend. With Perfect ground, you'll see that
there's actually a 0.02 dB gain improvement with the new distribution.
This is, of course, insignificant, but it does show that things are
working as they should.


next iteration:

cut that sucker down half again (and remove the load):
Impedance = 1.59 - J 624.6 ohms
Something tells me that this isn't off the scale of the perfect
comparison.
best gain:
0.25dBi
Hmm, the trend seems to go counter to intuition.

That's because you didn't understand the reason for the trend in the
first place. What's happening now is that the gain reduction caused by
the changed distribution is no longer overwhelmed by the gain increase
caused by the interaction with real ground. Again, go to Perfect ground
and you'll see that the trend of less gain as the antenna shortens is
continuing as exepected.


next iteration:

-sigh- what charms could loading bring us?
load = 1220 Ohms Xl up 55%
Impedance = 3.791 + J 1.232 ohms
more than doubled the Rr?
best gain:
0.23dBi


And with Perfect ground, the gain is the same within 0.01 dB with and
without the load -- the modified current distribution wasn't enough to
make any significant difference in the pattern and hence the gain.

Now, all of this is for a source that is a constant current generator;
we've monkeyed with the current distribution and put more resistance
(Rr?) into the equation with loading; and each time loading craps in
the punch bowl.

So much for theories of Rr being modified by loading.

Everything you've done shows that Rr is modified by loading. Rr at the
feedpoint is simply the resistance at the feedpoint. And it clearly
changes when you insert the load. What makes you think that the Rr isn't
changing?

I would
appreciate other effort in kind to correct any oversights I've made
(not just the usual palaver of tedious "explanations" - especially
those sophmoric studies of current-in/current-out).

Perhaps you're expecting the gain to vary in the same way as Rr. But you
see, gain will change with Rr only if the pattern shape stays the same.
And each time you insert the load, the current distribution changes,
which changes the shape of the pattern, which changes the gain. This is
the gain change you're seeing as you change the antenna length and add
loading. The main relationship between Rr and gain is the efficiency.
The antennas you've modeled are so close to being 100% efficient that
increasing Rr has no appreciable effect on gain. Check it yourself --
make the antenna 100% efficient by removing the wire loss and notice
that there's no change in gain (maybe 0.01 dB with the full size antenna).

But now repeat your experiments with, say, a 10 ohm resistive load at
the base to simulate ground system loss. And you'll see that the gain
improves dramatically as your loading increases Rr (the feedpoint
resistance). This is due to the improved efficiency you gain by
increasing Rr.

Roy Lewallen, W7EL

Richard Clark wrote:

On Fri, 05 Nov 2004 10:45:57 -0800, Jim Kelley
wrote:


I have a question. Can you express the mathematical and/or physical
relationship between Rr and antenna gain? It would sure help to clarify
the point you were trying to make.


Hi Jim,

I would have thought someone else could, given the bandwidth of
discussion in making the current taper shorter and the constant
current section longer. Testing does not bear their facile
relationship out however, and for the topic of a short antenna
(otherwise, why are we talking about loading coils?) it would seem
that antenna gain is immutable over several octaves below a
quarterwave length.

Of course, I coulda done something wrong. I did use a commonly
available design. I did use a commonly available modeler. I even may
have done the wrong thing in choosing a design that could be evaluated
for free. Perhaps I erred in providing the cogent details of
construction. It took all of 20 minutes to accomplish (far less time
than that expended in theories of current-in/current-out). These
technical hurdles appear to have set the bar too high for my work's
refutation in kind. I appreciate that "it's hard work!" ;-)

To answer your question, if you just abandon the perfect load, then
you stand to achieve a higher gain. If you shorten the antenna, then
you stand to achieve a higher gain. There is no change in Rr with the
addition of Xl. Hence the mathematical relationship for an antenna
shorter than quarterwave would be suggested as:
gain ~ 1/Rr
gain ~ 1/Xl
Rr Z

Don't take this gain to the bank however.

Point being that antenna gain has spatial implications which Rr by
itself could not provide in the solutions.

One should conclude from your results (very nice work, by the way) that
the modeler apparently doesn't figure Xl as contributing to the
radiation resistance. But isn't that basically the crux of the argument
here - whether or not that is in fact the case? If not, then we would
have to conclude that loading coil has zero physical and electrical
length, and that the impedance is constant from one end to the other.
Obviously I could be wrong, but I think those are the assumptions made
in your modeling software. On the other hand, if the impedance of the
coil is not constant from one end to the other, and it in fact does have
some real physical and/or electrical length, then I think the radiation
resistance of the antenna would have to be effected by its presence in
the circuit. That is, if indeed Ro is the integral of disributed r
along the entire physical and/or electrical length of the antenna
(credit for that formula going to an esteemed contributor to this
newsgroup earlier today). Or perhaps more concisely put, if the loading
coil itself contributes to the field radiating from the antenna, then it
should likewise have a Rr associated with it. The converse would of
course still be true.

73, Jim AC6XG

On Fri, 05 Nov 2004 13:06:40 -0800, Roy Lewallen
wrote:

What makes you think that the Rr isn't changing?

Hi Roy,

With what?

I have offered a very ascetic report of very simple actions from very
simple terms. You have chosen to change those terms to fit your own
answer (I do not choose to put this into the context of a perfect
world). Please offer effort in kind, or point out what error I've
made instead of what error I might have made if something were changed
from my model.

73's
Richard Clark, KB7QHC

On Fri, 05 Nov 2004 13:37:27 -0800, Jim Kelley
wrote:

Point being that antenna gain has spatial implications which Rr by
itself could not provide in the solutions.

Hi Jim,

Not sure where this is going, so I will stand with my own statements.

One should conclude from your results (very nice work, by the way) that
the modeler apparently doesn't figure Xl as contributing to the
radiation resistance.

Again, words. I would offer that Xl does not adjust Rr (insofar as it
does adjust drivepoint Z). Let me add - much (there are miniscule
differences).

But isn't that basically the crux of the argument
here - whether or not that is in fact the case? If not, then we would
have to conclude that loading coil has zero physical and electrical
length, and that the impedance is constant from one end to the other.

As I say above, it is not a difference of ZERO it is a miniscule
difference (with a negative correlation). I will leave it to others
to recapture (or diminish) gain through helix building. I am
satisfied those returns will be equally diminutive.

Obviously I could be wrong, but I think those are the assumptions made
in your modeling software.

We both could be wrong. No one has yet to step up to the bar and
offer work in kind.

On the other hand, if the impedance of the
coil is not constant from one end to the other, and it in fact does have
some real physical and/or electrical length, then I think the radiation
resistance of the antenna would have to be effected by its presence in
the circuit. That is, if indeed Ro is the integral of disributed r
along the entire physical and/or electrical length of the antenna
(credit for that formula going to an esteemed contributor to this
newsgroup earlier today). Or perhaps more concisely put, if the loading
coil itself contributes to the field radiating from the antenna, then it
should likewise have a Rr associated with it. The converse would of
course still be true.

This returns us to matters of degree. By simple observation comparing
the standard full sized radiator to ANY of the iterations, it is
obvious that nothing significant can be said of the physicality of the
load, much less its contribution. In other words, is there some
magical coil or magical placement that would create a short
super-radiator that exceeds the performance of the standard
quarterwave? [no here can recognize a eh/cfa claim?]

Let's put a handicap on this. Is there some magic combination of
coil/position that would even EQUAL the performance of the standard
quarterwave?

73's
Richard Clark, KB7QHC