Cecil Moore wrote:

wrote:
Regardless of whether there is an alternative explanation,
you should reject the reflected power model because....
In general, IT DOES NOT WORK.

In general, our feedline losses are low enough that it does
work. In general on HF, we are dealing with near-resistive
Z0's and Z0-matched systems.

There seems to be a bit of a vocabulary problem. The 'general
case' is the one that is more encompassing as in 'general
relativity' when compared to 'special relativity'.

So in your passage above, you are agreeing with my assertion.

In GENERAL, IT DOES NOT WORK.

In the specific case of RF, "our feedline losses are [usually]
low enough that it does work."
In the specific case of HF, "we are [usually] dealing with
near-resistive Z0's and Z0-matched systems."

With which I have no dispute. But that still leaves us with....

In GENERAL, IT DOES NOT WORK.

This strongly suggests a flaw in the model.

As has been aptly demonstrated in another thread, it does
not work for lines with complex Z0.

Actually it does. All one has to do is take the power interference
terms into account.

Exactly my point. So now the net power is no longer the sum of
the forward and reflected power; there is a third term which is
neither the forward nor the reflected power.

In GENERAL, IT DOES NOT WORK.

This, of course, will not prevent you from taking advantage
of it where it does work. But always remember that it ONLY
works in special cases.

With the possible exception of QED, that statement is true of ALL
math models, including yours. Yours only works in the special case
of perfect steady-state conditions

I am unsure what you think my model is. Perhaps you could elaborate?

In any case, my argument is that in GENERAL, the reflected power
model DOES NOT WORK. This is independent of whether I (or anyone)
has an alternative which does work.

....Keith

David Robbins wrote:

i'll agree with that... the ubiquitous 'SWR' meter provides useful
information for real world application, its easy to read, and easy to use.
Just because it may not be reading exactly what the name implies doesn't
reduce its usefulness.

On the one hand, it is still useful for what it does.

On the other hand, poor names have lead many to a mis-understanding of
how it works.

So overall, it has been less useful than if it were not mis-named.

....Keith

pez wrote:

| wrote:
| ...
| As has been aptly demonstrated in another thread, it does
| not work for lines with complex Z0.
| ...

Dear Keith,

Could you tell me please in which thread?

It was a thread started by Roy Lewellan titled "Complex line
Z0: A numerical example" to which I refer.

On the assumption that you have access to and that google will give
the same answer to you that it gives to me, try...

http://groups.google.ca/groups?hl=en...vl2kp2cdlork04

....Keith

On Sun, 21 Sep 2003 15:29:26 -0500, Cecil Moore
wrote:
It is all explained in Chipman's "Transmission Lines". Please take the time
to read it and understand it

:-)

Good example. But let's suppose you've never seen any rectangle that
wasn't square. You've learned that you only need to measure one side
(with a Bird side-meter, undoubtedly) in order to determine the area.
Works fine. Always has. You swear up and down that the area of a
rectangular figure is always the square of one side. Then someone gives
you a rectangle. Worse yet, they claim there's something called a
rectangle, which you've never seen.

It's been really interesting to see how the various participants in this
discussion react to this new concept.

Roy Lewallen, W7EL

Richard Harrison wrote:
Keith wrote:
"Scientists are usually interested in producing models which will allow
them to predict the behaviour of the real world.

True. Models must be adjusted to reality, not the other way around. But,
once the model is verified it becomes useful.

You don`t have to measure the area of a rectangle with a planimeter once
you know that area is the product of the length and width of the
rectangle.

Best regards, Richard Harrison, KB5WZI

Radio913 wrote:

"Scientists" are also human too, and tend to want to disregard or not
even
try to measure data that may contradict their models. This makes them
feel
comfortable that they are "right".

I completely agree.

So can you overcome your "tend[ancy] to want to disregard or
not even try to measure data that may contradict their models."?

I'll think about it after you tell us what you get when you measure the
end of the inductor.

I've been to the lab.

May I suggest that it is now your turn to do so.

Otherwise you are simply adding to the evidence that you are having
difficulty overcoming a "tend[ancy] to want to disregard or not even
try to measure data that may contradict [your] models."

....Keith

Keith wrote:
"Some of the authors you quote are not so convinced of their (waves)
reality."

Symbols merely represent reality but are important to the exchange of
ideas just the same. The effects seen on transmission lines are reliably
explained and predicted by wave action. In one of my physics classes
over a half century ago, the prof asked another student a question about
atoms. The reply was that the student had never been inside an atom.
Neither the prof nor anyone else seemed impressed with the retention of
the student, but the prof agreed that he had never been inside an atom
either, but found atomic theory useful.

Terman is as reliable as anyone I know of, and he says:
"The voltage and current existing on a transmission line as given by
Eqs. (4-6) can be conveniently exprerssed as the sum of the voltages and
currents of two waves, one traveling toward the receiving or load end of
the line, and is called the "incident wave" because it is incident upon
the load. The second wave can be thought of as traveling from the load
toward the generator end of the line; it is termed the "reflected wave",
and is generated at the load by reflection of the incident wave."

Terman has no qualms, it seems, but says "regarded as traveling". Those
aren`t weasel words. Terman is more direct on page one in the opening
sentance:
"Electrical energy that has escaped into free space exists in the form
of electromagnetic waves."

How else could their energy be transferred at the speed of light?

Best regards, Richard Harrison, KB5WZI

Keith wrote:
"---does the reader believe the markings on the scale and think that it
is actually MEASURING the power in a forward and reverse wave?"

The wattmeter markings have been calibrated to indicate watts. One only
must measure a quantity proportional to watts then interpret that
accurately.

A speedometer indicates miles per hour but gets that from electricity
which is proportional to speed. Neither miles nor hours are measured.

Best regards, Richard Harrison, KB5WZI

Cecil,

I don't have a schematic for the Daiwa. So, I don't really know what it was
measuring; but, I think more than likely, the voltage that reached the
meter. If the scale were calibrated in gallons per minute, I might have read
2.5 gallons per minute.

Tam/WB2TT
"Cecil Moore" wrote in message
...
Tarmo Tammaru wrote:
Amen to that. I turned down the power on my transmitter, and measured P
forward and P rev while feeding about 100 feet of unterminated 9913. I
then
REMOVED the coax; i.e. there was nothing connected to the output side of
the
meter. Still measured the same Pf and Pr. (Daiwa meter)

Of course, you were simply getting a same-cycle reflection. The reflected
wave model is consistent. If the open-circuit is at the transmitter
terminal,
all the power is reflected immediately.
--
73, Cecil http://www.qsl.net/w5dxp



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Richard Harrison wrote:

Keith wrote:
"---does the reader believe the markings on the scale and think that it
is actually MEASURING the power in a forward and reverse wave?"

One only must measure a quantity proportional to watts then interpret
that accurately.

So true. But the quantities being measured are line volts and line amps
and neither is proportional to incident or reflected watts.

Much happens to the measured voltage and current before the result is
inaccurately interpreted as forward and reverse power.

....Keith