Loading Coils; was : Vincent antenna
 

Richard Clark wrote:
"AI4QJ" wrote:
standing wave currents

When these three keywords are braced with quotes, Google reveals all
of 19, non-duplicated sources.

When the keywords, "current in standing waves", is used
Google comes up with 294,000 hits.

Cecil's
reconstructed, but revisionist measurement that disputes Tom's data
published on the web; it was nearly identical to Tom's when phases
were reconciled in his test arrangement.

This is absolutely not true. One wonders what you have
to gain by falsifying technical data. One wonders why
you have not responded to my request to explain the
"Load Dat" results of http://www.w5dxp.com/coil512.ex
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Roy Lewallen wrote:
I think it might be useful to say a little more about standing waves.

Imagine a single lossless transmission line with a sine wave source at
one end and a load at the other. Begin with a load equal to the line's
Z0. Make a graph of the magnitude of the current or voltage as a
function of distance from the source. With the Z0 load, the magnitude
will be the same all along the line so your graph will be a straight
line. This is a "flat" line, with no standing wave. A probe sitting at
one spot would show the instantaneous voltage or current amplitude going
up and down in a sinusoidal manner. A probe a bit farther down the line
would look the same, but delayed; there's a phase difference between the
voltages or currents at the two points. The phase difference is equal to
the line's physical length in degrees divided by the velocity factor.

I've done exactly that with current using EZNEC. The traveling wave
graph is on the left at http://www.w5dxp.com/travstnd.gif

The standing wave current graph described in Roy's next quoted
paragraph below is on the right. The tabulated data provided by
EZNEC is at the bottom.

If standing-wave current is all that exists, EZNEC faithfully
reports the amplitude and phase of the standing-wave current.

If traveling-wave current is all that exists, EZNEC faithfully
reports the amplitude and phase of the traveling-wave current.

At the most extreme case of mismatch -- an open, short, or purely
reactive load, resulting in an infinite SWR -- the amplitude of the
standing wave along the line goes from zero to twice the value it had
when the line was flat. And a really interesting thing happens to the
phase of the voltages and currents on the line. Remember how as the
mismatch got worse, the voltage and current phase difference between two
points got farther and farther away from the electrical line length
between them? Well, when the SWR is infinite, it's gotten to the point
where the voltage or current phase remains the same for a distance of a
half electrical wavelength, then abruptly changes 180 degrees, repeating
every half electrical wavelength. Some antennas behave in some (and only
some) ways like transmission lines, and you'll find that modeling
programs report just this behavior of the phase of the current along a
straight wire antenna.

The question is, Roy, since as you say, "the current phase remains
the same for a distance of a half electrical wavelength", how can
you possibly use that same current to measure the phase shift
through a coil and convert your reading to a delay through the
coil? If the phase of the current doesn't change over the entire
1/2 wavelength, it certainly doesn't change through the coil. What
you have proven above is that your and W8JI's previously reported
coil measurements are meaningless and that the only valid way to
measure the delay through a coil is to use the traveling wave
current described in your first paragraph above.

What you are saying in the above paragraph is that the current in
a high-SWR environment carries virtually no phase information. So
the question remains:

WHY DO YOU THINK THAT PHASE MEASUREMENTS OF STANDING WAVE CURRENT,
GIVEN ITS VIRTUALLY UNCHANGING PHASE, WILL YIELD ANY USEFUL
INFORMATION ABOUT THE DELAY THROUGH A LOADING COIL?

You did measure the phase shift through the coil but the
measurement was meaningless and the conclusions invalid.
We already knew it would be close to zero and bear no
relationship to the delay through the loading coil -
BECAUSE THERE IS VIRTUALLY NO PHASE INFORMATION IN THE
PHASE OF STANDING WAVES.

The phase information in standing waves is in the amplitude
but you obviously don't realize that fact since you continue
to talk about the current "drop" through the coil being due
to losses, radiation, and leakage to the environment. If there
were zero losses, zero radiation, and zero leakage, the current
"drop" would still be there as a result of nothing more than
the superposition of the forward and reflected waves.

I hope this helps in clarifying the meanings of traveling and standing
waves, voltage and current along a transmission line.

I agree with what you have said in this posting. Unfortunately
for you, what you said in this posting contradicts and invalidates
the conclusions that you and W8JI drew from your phase
measurements of current through a loading coil in a standing-
wave antenna.

Out of one side of you mouth, you tell us that the standing-
wave current phase is unchanging over 1/2 wavelength. Out of
the other side of you mouth, you tell us that same current can
be used to measure the delay through a loading coil. Please
pick one side or the other - they cannot both be right.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:

Ian, I apologize for yanking your chain. It is a bad
habit of mine.

Ian White GM3SEK wrote:
Cecil Moore wrote:
Yep, that's exactly as I quoted it.

Once could have been a mistake. Twice is deliberate, dishonest
manipulation.

Ian, your first sentence was false and I responded to it.
No amount of words that you post after the first false
statement will make it true. There *are* glitches in the
standard circuit models for inductance and capacitance
because they do not agree with Maxwell's equations.
There was nothing dishonest about my replies. In fact,
I was just following netnews rules.

Continuing: If your model worked, W8JI would not have
measured a 3ns delay on 4 MHz through a 2" dia, 100 T,
10" long coil. It is, in fact, your flawed model that
allowed him to come to the false conclusions that he
did. And I notice your model got you in trouble because
you did not offer one word of objection to his obviously
impossible conclusions.

You guys are religiously addicted to models that do
not correspond to reality and it gets you into a lot
of trouble including passing false information along
to your naive readers.

It appears that we are on the verge of proving that a
3 ns delay through the above coil is impossible no
matter what your model says.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Hi Roy,

Could I add this observation? Both traveling waves and standing waves
can be measured. A single volt meter or ammeter will measure the
standing wave which is the sum of the traveling waves.. A DIRECTIONAL
volt meter or ammeter will measure only the traveling wave within the
design direction, but can not distinguish between components from
multiple reflections that might combine.

A directional voltmeter or ammeter will measure the same voltage or
current no matter where it is placed in the transmission line under
steady state conditions, assuming no resistive losses in the
transmission line.

73, Roger, W7WKB

Roy Lewallen wrote:
I think it might be useful to say a little more about standing waves.

Imagine a single lossless transmission line with a sine wave source at
one end and a load at the other. Begin with a load equal to the line's
Z0. Make a graph of the magnitude of the current or voltage as a
function of distance from the source. With the Z0 load, the magnitude
will be the same all along the line so your graph will be a straight
line. This is a "flat" line, with no standing wave. A probe sitting at
one spot would show the instantaneous voltage or current amplitude
going up and down in a sinusoidal manner. A probe a bit farther down
the line would look the same, but delayed; there's a phase difference
between the voltages or currents at the two points. The phase
difference is equal to the line's physical length in degrees divided
by the velocity factor.

Now change the load so the line is slightly mismatched. A standing
wave will appear -- the graph of amplitude vs distance won't be flat
any longer, but will have a ripple added to its previous constant
value. (The VSWR is, by definition, the ratio of the highest to the
lowest values of the voltage envelope on a line long enough to have a
full maximum and minimum. The current SWR is the same.) The maxima and
minima of the ripple don't move, hence the name "standing wave". If we
look at the instantaneous voltage or current at a single point, it
will go up and down in step with the source as before. If we also look
at the second point, it'll also go up and down as before, and there
will be a phase angle between the two. But there are two interesting
differences from the flat line: One is that the amplitudes at the two
points are now unequal unless they're an integral number of half
electrical wavelengths apart (or a few other special cases). The other
is that the phase shift isn't the same as before. There's still a
phase shift between the two points, but it's no longer equal to the
electrical length of the line between the points. We'll find that
either the voltage has shifted more and the current less, or vice
versa depending on the load and which points we've chosen. But at
every point the current and voltage still have phase angles which
change with position along the line. That is to say, the voltage or
current at one point is delayed compared to the voltage or current at
the other.

As the mismatch gets more extreme (i.e., the SWR increases), the
magnitudes at the two points get more different, and the phase
deviates farther from the electrical length of line between them.
(This is why you can't expect phased array "delay lines" to provide a
delay equal to the lines' electrical lengths when they're not
terminated with Z0.)

At the most extreme case of mismatch -- an open, short, or purely
reactive load, resulting in an infinite SWR -- the amplitude of the
standing wave along the line goes from zero to twice the value it had
when the line was flat. And a really interesting thing happens to the
phase of the voltages and currents on the line. Remember how as the
mismatch got worse, the voltage and current phase difference between
two points got farther and farther away from the electrical line
length between them? Well, when the SWR is infinite, it's gotten to
the point where the voltage or current phase remains the same for a
distance of a half electrical wavelength, then abruptly changes 180
degrees, repeating every half electrical wavelength. Some antennas
behave in some (and only some) ways like transmission lines, and
you'll find that modeling programs report just this behavior of the
phase of the current along a straight wire antenna.

The standing wave and all the characteristics of the voltage and
current (e.g., how their magnitude and phase varies with position
along the line) follow directly from an analysis of forward and
reflected traveling waves on the line. The voltage or current at any
point is simply the sum of the two waves at that point, and they have
the properties I've just described.

I hope this helps in clarifying the meanings of traveling and standing
waves, voltage and current along a transmission line. I'm sure there
are lots of good graphical illustrations available -- but some bad
ones too. Hopefully keeping this explanation in mind when you look at
the nice graphics displays will help you sort the bad ones from the good.

Roy Lewallen, W7EL

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:
AI4QJ wrote:
Roy, this is the part I don't understand about some people posting on
this thread. A standing wave does *not* have a phase shift.

Gene said the same thing many months ago:

Gene Fuller, W4SZ wrote:
In a standing wave antenna problem, such as the one you describe,
there is no remaining phase information. Any specific phase
characteristics of the traveling waves died out when the startup
transients died out.

Phase is gone. Kaput. Vanished. Cannot be recovered. Never to be
seen again.

Cecil,

As usual, you continue to take things out of context. That quote
specifically referred to the (kz-wt) "phase". Simple examination of the
ideal standing wave equation shows my quoted comment to be correct.

However, I have also pointed out on several occasions that there are
multiple definitions for phase. It is not necessary to have a (kz-wt)
term in order to have valid and useful "phase" in a circuit.

But you already know that.

73,
Gene
W4SZ

Loading Coils; was : Vincent antenna
 

On Sun, 09 Dec 2007 03:32:59 -0800, Roy Lewallen
wrote:

Hopefully keeping this explanation in mind when you look at the nice
graphics displays will help you sort the bad ones from the good.

Hi Roy,

Your description of the Phase and the SWR contribution to how it is
perceived was excellent; and with enough words to get from start to
finish and be thorough.

It deserves acknowledgement.

However, with this buried beneath all the trash of this thread, it
should be included in your own site's miscellaneous files for easier
reference, because the misperceptions for this topic (and Cecil
stepped right up to shove a stick in the spokes) just aren't going to
go away.

73's
Richard Clark, KB7QHC

Loading Coils; was : Vincent antenna
 

On Sun, 09 Dec 2007 14:40:43 GMT, Cecil Moore
wrote:

Cecil's
reconstructed, but revisionist measurement that disputes Tom's data
published on the web; it was nearly identical to Tom's when phases
were reconciled in his test arrangement.

This is absolutely not true.

This is merely the hysterical reaction to personal embarassment.

One wonders what you have
to gain by falsifying technical data.

The data was wholly of your own supply. As I pointed out, the obvious
conclusion you reject in my quote above could only be satisfied by
your impeaching your own data. ;-)

One wonders why
you have not responded to my request to explain the
"Load Dat" results of http://www.w5dxp.com/coil512.ex

"One" is the keyword and luckily it is only "one." If other's pressed
me, I might be motivated, but you don't have that capacity.

Count yourself lucky to have mooched the validation you have from the
few who haven't been around the block with you.

Loading Coils; was : Vincent antenna
 

On Sun, 09 Dec 2007 14:25:35 GMT, Cecil Moore
wrote:

Richard Clark wrote:
His proving Tom's delay was no better
than his own measurement demonstrated this easily.

Here's your logic, Richard. You ask me how much
is two plus two. I don't respond. Your conclusion
is that I don't know how much is two plus two.
The truth is that I simply tired of your nonsense.

All would agree we have conclusions that are both indisputable. ;-)

I hope others will observe these six lines, one exchange, exhibits the
classic low hanging fruit that can be gathered by simply drilling down
through them! It really is just that simple and Cecil always hands it
to me on a silver plate.

Loading Coils; was : Vincent antenna
 

Keith Dysart wrote:
The key point is that since 62.5 nsec represents 1/4WL at the
frequency of interest, if the line was 1/4WL long, you would
find things that happen every 62.5 nsec.

No, that is not a key point. If we figure out some way
to get a 90 degree phase shift to happen in 10 nsec, so
be it. There is nothing that forces a phase shift to
take the same amount of time as it does in a transmission
line.

There is no doubt that all the variants discussed do share one
property with a 1/4WL open stub; the input impedance after a
long settling time is the same. But other properties, particularly
settling time, are quite different.

I don't have a problem with that statement. Everything I
have talked about is in regards to steady-state conditions.

If you are saying that along the transmission line there is a point
every 125 nsec where the impedance is 0, I would agree for
a constant impedance line, but if you change the impedance then
the points on either side of the discontinuity are not 125 nsec
apart.

If I never said that, your statement would still be true.
I agree and never said otherwise.

But 46.4 + 10 does not equal 90.

Yet we know for certain that the reflected wave has undergone
a 90 degree phase shift or else it wouldn't be in phase with
the forward wave at the feedpoint. That additional phase shift
has no time constraint. Deduction will tell one where it is
located. It is not in the 600 ohm section. It is not in the
100 ohm section. It is not at the open end of the stub. Since
the only location left is the impedance discontinuity, it must
occur at that point and indeed the Smith Chart shows us that
is exactly where it occurs in an exactly predictable value.
"Elementary, my dear Watson".
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

On Sun, 09 Dec 2007 15:16:52 GMT, Cecil Moore
wrote:

If standing-wave current is all that exists, EZNEC faithfully
reports the amplitude and phase of the standing-wave current.

It would appear that our author has some doubt about the statement
above to have prefaced it with "if." A grammarian would point out
that there is no corresponding "then." As this doubt is obviously a
contorted product of tension, I won't look for spelling errors that
Cecil would expect me to find.

If traveling-wave current is all that exists, EZNEC faithfully
reports the amplitude and phase of the traveling-wave current.

Again, the same nagging doubt - "if" indeed.

We can summarily answer that doubt by immediately dismissing it. There
is no such thing as standing-wave or traveling-wave current. The
statements above with the doubting "if" stripped out would read:

The current found in the solution of the standing-wave is all that
exists, EZNEC faithfully reports the amplitude and phase of that
current.

The current found in the solution of the traveling-wave is all
that exists, EZNEC faithfully reports the amplitude and
phase of that current.

Again, drilling down yields another silver plate of low hanging fruit.

73's
Richard Clark, KB7QHC