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Roy Lewallen wrote:
But neither the
amplitude nor the "phase" of the envelope known as the standing wave
will, by itself, tell you anything about the phase of the current at any
point along the line.

Yet, that is exactly the current you used for your
coil phase-shift measurements. Your position is
contradictory and indefensible.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Earlier, I had written:
"Likewise there are no glitches in the standard circuit models for
inductance and capacitance. They work just fine, for all cases where the
dimensions of the circuit are very small with respect to the wavelength,
so that distributed effects and radiation are negligible. Where those
assumptions are no longer accurate, we can extend the simple model to
include some corrections. But the most important point is, we always
know that we're building up from a solid foundation."

Cecil Moore wrote:
Ian White GM3SEK wrote:
Cecil Moore wrote:
Ian White GM3SEK wrote:
Likewise there are no glitches in the standard circuit models for
inductance and capacitance.

Really???? Just try your lumped inductance model on
a helical antenna and get back to us.
Yet more stinking dishonest quoting from Cecil. What I ACTUALLY
wrote was:
"Likewise there are no glitches in the standard circuit models for
inductance and capacitance.

Yep, that's exactly as I quoted it.

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

The beauty of Usenet is that it's now on permanent record.


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

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On Sat, 8 Dec 2007 22:58:42 -0500, "AI4QJ" wrote:

Remember, the system was *measured* to be 1/4W so the reflections must cause
a short every 125 nsec, no matter what is happening in between.

Hi Dan,

Keith was quite specific to separate the transient state from the
steady state such that a short is not available "every 125 nS." Most
125 nS, perhaps, but not initially and so not "every 125 nS." Trivial
distinction on the face of it, perhaps. When paired up with an
absolute statement that has been "proven" to be universally true, then
trivial is enough to sink the Titanic.

The smith chart and
phaser diagrams should work and are equivalent to using math.

There are two solutions: transient and steady states; there are two
maths. Cecil, in the same breath, manages to jump from one to the
other enough that you should be acquainted with both by now - or you
will be when you suddenly find yourself facing a paradox: Like why is
the band that is playing "Nearer, My God, to Thee" is at such an odd
sloping angle on the boat deck?

Fortunately it takes only a little effort to follow one line, and to
drill down to an absurdity. His proving Tom's delay was no better
than his own measurement demonstrated this easily. The drilling down
was in simply noting the particulars and skipping all the fluff of
trivial sidebars. Most folks find the fluff attractive and chase it
to no conclusion instead (that is how this thread accumulated 600
postings).

Keith, on the other hand, has the discipline to simply stick to one
issue, and drill down. Patience brings rewards in the end.

73's
Richard Clark, KB7QHC

Loading Coils; was : Vincent antenna
 

Ian White GM3SEK wrote:
... Where those
assumptions are no longer accurate, we can extend the simple model to
include some corrections. But the most important point is, we always
know that we're building up from a solid foundation."
...

In the profession which puts meat on my table, that/those are called
"magic numbers" and are a sure sign something is amiss, either with the
understanding of the problem(s), the methods or the person attempting
the solutions ...

Regards,
JS

Loading Coils; was : Vincent antenna
 

On Sat, 8 Dec 2007 23:59:56 -0500, "AI4QJ" wrote:

standing wave currents

Hi Dan,

When these three keywords are braced with quotes, Google reveals all
of 19, non-duplicated sources. Not a very compelling testimony to
this phrase's usage when the phrase "current standing wave" results in
at least 10 times that amount. Even more so, neither amount to many
references.

When googling the separate term Current from the phrase "standing
wave;" then the hits count climbs through the ceiling to nearly
200,000 links or 1000 to 10000 times the unique phrases above.

Simple deconstruction would suggest that
standing wave currents
is about as useful as downloading a windows patch from
www.micorsoft.com. Would you? (Try the link and see if you would
trust the source.)

Deconstruction aside, what I see missing in your enquiry into this
"current" is any question about what information it contains. I've
seen the suggestion of phase, and Roy has answered that, but in
isolation (no reference) there is magnitude only. 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.

Even here in the post you've responded to, Roy demonstrated the
normalization of scope channel's separate delays. Given it was his
trade for umpteen years in their design (as it was my trade to
calibrate them), and Cecil's trade was building flip flops (the only
phase there is 180 degrees and nothing in between); then who has a
better grasp on the fundamentals? An IQ of 260 doesn't mean anyone is
educated or has a skill.

73's
Richard Clark, KB7QHC

Loading Coils; was : Vincent antenna
 

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

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On Dec 8, 10:58 pm, "AI4QJ" wrote:
"Keith Dysart" wrote in message
On Dec 8, 3:15 pm, "AI4QJ" wrote:
In this example, we have transmission lines, not an antenna or antenna
coil.
The total phase shift is 90 degrees or 62.5 nsec.

Only with great stretching.

The 10 degree 100 ohm line contributes 6.94nsec,

Correct.

the 43 degree 600 ohm line contributes 29.86 nsec.

Correct.

But now think in the time domain for a bit.
29.86 nsec after the signal is first applied it reaches the
discontinuity. 29.86 nsec later the first reflection arrives
back at the start. 13.8 nsec later the first reflection from
the end of the 100 ohm section arrives back at the start.
It takes many more reflections of reflections before the
impedance at the input starts to look like a short.

Nowhere in here will you be able to find anything that
happens in 62.5 nsec.

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.

The values returned back to the feed point are superimposed
in the time domain, adding and subtracting, but the whole system should
(*does*) still act like a 1/4W stub at 4MHz.

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.

A 1/4W stub could consist of
1..N series transmission lines of different impedances provided they were
cut to the correct lengths.

Quite true. And if your definition of 14WL stub was anything that
produced a short, I would agree that it is self-consistent
but that it is probably not too useful.

Remember, the system was *measured* to be 1/4W so the reflections
must cause a short every 125 nsec, no matter what is happening in between.

If I understand what your are saying, then NO. Consider the short
itself.
There is no delay what-so-ever.

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.

The task is to use the math to verify the measurement. The smith chart and
phaser diagrams should work and are equivalent to using math. Time domain is
possible too but no way I would ever go to that trouble on usenet at least!
Or do you think the measurement was wrong?-

I have no disagreement with the resulting numbers.

But 46.4 + 10 does not equal 90. Subtracting (46.4 + 10)
from 90 does not yield a useful number, though if you
decide that the sum MUST be 90 for some reason, then
you do have the number that will do that.

....Keith

Loading Coils; was : Vincent antenna
 

Ian White GM3SEK wrote:
Once could have been a mistake. Twice is deliberate, dishonest
manipulation.

Absolutely nothing dishonest about it.

Once you make a mistake, Ian, it doesn't matter what
you say after the mistake. What I disagreed with was
your mistake and didn't bother quoting the rest. I
believe that is part of the netnews guidelines.

So I challenge you again. Given a two wavelength
slinky dipole, please use your lumped constant
model to predict the current in the antenna.

Of course, you cannot and will not do that.
--
73, Cecil http://www.w5dxp.com

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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.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

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.

You said:
Likewise there are no glitches in the standard circuit
models for inductance and capacitance.

But there are glitches in that model so that is a false
statement to which I replied. Nothing you can say after
that statement will make it true.

I am sorry that you get so upset when challenged but
you are wrong about a lot of things.
--
73, Cecil http://www.w5dxp.com