Revisiting the Power Explanation
 

One of the issues discussed in this thread that Owen originated concerned whether or not reflected power
enters the power amp and dissipates as heat in the plates of the amp. Some of the posters apparently are
unable to appreciate that the reflected power does not cause heating of the amp, unless the reflected power
detunes the amp and the amp is left detuned from resonance, which of course is not the correct manner of
operating the amp.

In the last post of the original thread I presented the details of an experiment I performed (one of many
using the same procedure) on a Kenwood TS-830S transceiver that proves how and why reflected power in no way
causes heating of the amp when the amp is properly adjusted in the presence of the reflected power.

Usually, such a presentation as in the last post in that thread evokes a great deal of response, as for
example, Art Unwin's. So I'm somewhat surprised, and a little disappointed that my post has resulted in total
silence. Have my efforts in helping to solve the problem gone for naught?

Walt, W2DU

Revisiting the Power Explanation
 

Walter Maxwell wrote:
Some of the posters apparently are
unable to appreciate that the reflected power does not cause heating of the amp, unless the reflected power
detunes the amp and the amp is left detuned from resonance, which of course is not the correct manner of
operating the amp.

Some would say that if "reflected power does not cause heating
of the amp", that proves that there is no power (or energy) in
the reflected waves. Those people obviously don't understand
the role of destructive and constructive interference during
the EM wave superposition process.
--
73, Cecil http://www.w5dxp.com

Revisiting the Power Explanation
 

On Tue, 20 Mar 2007 10:55:12 -0500, Cecil Moore wrote:

Walter Maxwell wrote:
Some of the posters apparently are
unable to appreciate that the reflected power does not cause heating of the amp, unless the reflected power
detunes the amp and the amp is left detuned from resonance, which of course is not the correct manner of
operating the amp.

Some would say that if "reflected power does not cause heating
of the amp", that proves that there is no power (or energy) in
the reflected waves. Those people obviously don't understand
the role of destructive and constructive interference during
the EM wave superposition process.

In addition, Cecil, the experiment also proves that the reflected power doesn't heat the plate, because the
output source resistance is non-dissipative.

Walt

Revisiting the Power Explanation
 

Cecil Moore wrote:

Some would say that if "reflected power does not cause heating
of the amp", that proves that there is no power (or energy) in
the reflected waves. Those people obviously don't understand
the role of destructive and constructive interference during
the EM wave superposition process.

Cecil,

What reflected waves?

An equally valid description in steady state, after all the transients
have died out, includes a standing wave containing the stored energy in
the line plus a forward traveling wave carrying the energy that does
make it through the load end of the line.

No need to account for any mythical power in the reflected waves.

This description matches your quotes from Hecht and from Ramo and
Whinnery that I attached a few days ago.

73,
Gene
W4SZ

Revisiting the Power Explanation
 

Gene Fuller wrote:
No need to account for any mythical power in the reflected waves.

How can you possibly deny the existence of the reverse
traveling wave and then be incapable of providing an
example of a standing wave existing without a reverse
traveling wave? Sounds like smoke, mirrors, and arm-
waving to me.
--
73, Cecil http://www.w5dxp.com

Revisiting the Power Explanation
 

Walter Maxwell wrote:
In addition, Cecil, the experiment also proves that the reflected power doesn't heat the plate, because the
output source resistance is non-dissipative.

I understand what happens to the direction and
momentum in the reflected wave when it encounters
an impedance discontinuity at some distance from
the source, e.g. a Z0-match.

What happens to the direction and momentum in the
reflected wave when it encounters a non-dissipative
resistance at the source?
--
73, Cecil http://www.w5dxp.com

Revisiting the Power Explanation
 

Gene, W4SZ wrote:
"No need to account for any mythical power in the reflected waves."

Cecil has an IEEE dictionary which defines power in terms of the voltage
and in-phase current passing a point.

Terman says on page 96 of his 1955 opus:
"The reflected wave is identical with the incident wave except that it
is traveling toward the generator."

Bird says of its Model 43 RF Directional "Thruline" Wattmeter:
"The forward wave travels (and its power flows) from the source to the
load. It has RF Voltage Ef and current If in phase, with Ef/If=Zo.

The reflected wave originates by reflection at the load, travels (and
its power flows) from the load back to the source, and also has an RF
voltage Er and current Ir in phase, with Er/Ir=Zo."

Best regards, Richard Harrison, KB5WZI

Revisiting the Power Explanation
 

Richard Harrison wrote:
Terman says on page 96 of his 1955 opus:
"The reflected wave is identical with the incident wave except that it
is traveling toward the generator."

Gene needs to tell us how the TV modulation that
causes ghosting makes its predictable round trips
to the source and back without the aid of the
reverse traveling wave.
--
73, Cecil http://www.w5dxp.com

Revisiting the Power Explanation
 

Cecil Moore wrote in news:7iYLh.73$Kd3.72
@newssvr27.news.prodigy.net:

Gene needs to tell us how the TV modulation that
causes ghosting makes its predictable round trips
to the source and back without the aid of the
reverse traveling wave.

Talk about echoes!

Cecil, at the time of writing, you have made 4 of the 7 responses to
Walt's posts, and there is nothing in what you have said that you haven't
said recently.

The language from various posters like:

"Some of the posters apparently are unable..."

"Some would say..."

"people obviously don't understand..."

"How can you possibly deny..."

doesn't seem to me the language of convicing arguments, much less proof,
from either side. They seem more a sign of the posters frustration, but
not otherwise convincing.

My guess is that this discussion will not converge on a convincing
outcome.

If the past is any indicator, just when agreement of two or three people
looks likely, someone will inject some noise like lets start dealing with
time domain and transient issues to prove that steady state analysis is
invalid in the practical sense, or this needs a photon explanation with
reference to a text no one is likely to have. It as though those posters
intended to wreck logical development and conclusion. Ah, but that is
USENET!

The basis of the assertion that a PA is naturally or magically conjugate
matched as a necessary consequence of adjustment or design for maximum
power output is based on an leveraging the Maximum Power Transfer Theorem
which depends on a linear source. I don't recall seeing experimental
results to convincingly demonstrate that the PA is a linear source,
though I have seen those that suggest otherwise. If the source cannot be
proven to be sufficiently close to a linear source, then the basis for
arguing the implicit conjugate match dissolves.

No one has yet come up with a quantitative proof that in the general case
PAs of all kinds have an equivalent source impedance the conjugate of
their load, nor convincing experiments that would place bounds on the
reflection coefficient looking into the PA for practical transmitters.

No one has demonstrated that using equivalent impedances etc is not a
valid analysis of the steady state behaviour.

Owen

Revisiting the Power Explanation
 

On Tue, 20 Mar 2007 22:06:35 GMT, Owen Duffy wrote:

I don't recall seeing experimental
results to convincingly demonstrate that the PA is a linear source,
though I have seen those that suggest otherwise. If the source cannot be
proven to be sufficiently close to a linear source, then the basis for
arguing the implicit conjugate match dissolves.

Owen, despite our previous discussion, I have explained many times that even though the PA source upstream of
the tank circuit is non-linear (and no one's saying it isn't), the energy storage in the tank makes the output
of the tank a linear source, no matter what the shape of the current wave form may be at the input. The output
of the tank is proved linear because the voltage/current ratio at the output is non-varying and the shape of
the voltage and current wave forms are essentially sine waves. Consequently, the output circuit can be
represented by a Thevenin source that supports both a conjugate match and the maximum power transfer theorem.

Are you now denying that the output of a PA with the routine Q of 10 to 12 is not substantially a sine wave?
If you agree that it is a sine wave, then why are you arguing that there is no basis for a conjugate match?

However, none of the responses above respond to the issue of why the reflected power does not cause heating of
the amp, which is what my treatise was all about.

Walt, W2DU

Revisiting the Power Explanation
 

On Tue, 20 Mar 2007 22:57:48 GMT, Walter Maxwell wrote:

On Tue, 20 Mar 2007 22:06:35 GMT, Owen Duffy wrote:

I don't recall seeing experimental
results to convincingly demonstrate that the PA is a linear source,
though I have seen those that suggest otherwise. If the source cannot be
proven to be sufficiently close to a linear source, then the basis for
arguing the implicit conjugate match dissolves.

Owen, despite our previous discussion, I have explained many times that even though the PA source upstream of
the tank circuit is non-linear (and no one's saying it isn't), the energy storage in the tank makes the output
of the tank a linear source, no matter what the shape of the current wave form may be at the input. The output
of the tank is proved linear because the voltage/current ratio at the output is non-varying and the shape of
the voltage and current wave forms are essentially sine waves. Consequently, the output circuit can be
represented by a Thevenin source that supports both a conjugate match and the maximum power transfer theorem.

Are you now denying that the output of a PA with the routine Q of 10 to 12 is not substantially a sine wave?
If you agree that it is a sine wave, then why are you arguing that there is no basis for a conjugate match?

However, none of the responses above respond to the issue of why the reflected power does not cause heating of
the amp, which is what my treatise was all about.

Walt, W2DU

In the fourth line in the first paragraph above the word 'time' was inadvertantly omitted. It should have read
....the output is non-time varying and the shape...

Sorry about that,

Walt, W2DU

Revisiting the Power Explanation
 

"Owen Duffy"
No one has demonstrated that using equivalent impedances etc
is not a valid analysis of the steady state behaviour.
_________

A reflection is a reflection. The reflection of a ~steady-state r-f source
may produce a different perceived/effective result than if that source
includes transients (modulation), but such does not negate the existence of
reverse/reflected power in the steady-state case.

Decades of experience with analog broadcast TV transmission systems
demonstrate that the reflected power from a mismatch at the transmit antenna
produces an amplitude variation (ripple) and other effects across the r-f
and demodulated video channel bandwidths that are directly related to the
magnitude of the antenna mismatch and the round-trip propagation time of the
transmission line between the tx and the antenna (period = 1 cycle per ~491
feet of air-dielectric line).

This is evident not only from accurate measurements made via a highly
directional r-f coupler sampling forward power at the tx end of the
transmission line, but also from results seen on the screen of TV sets
viewing those transmissions. I suspect, Owen, that you would agree that
this example originates from a "practical" system.

The r-f power supplied even by a CW source is subject to the same amount of
reflected power for a given antenna mismatch, which will have an appropriate
effect on system performance. Whether or not that reflected
power/performance effect is important (or even recognized as existent) is
the issue at hand.

RF

Revisiting the Power Explanation
 

"Walter Maxwell" wrote
... I have explained many times that even though the PA source
upstream of the tank circuit is non-linear (and no one's saying it isn't),
the energy storage in the tank makes the output of the tank a linear
source, no matter what the shape of the current wave form may be
at the input. The output of the tank is proved linear because the
voltage/current ratio at the output is non-varying and the shape of
the voltage and current wave forms are essentially sine waves.
Consequently, the output circuit can be represented by a Thevenin
source that supports both a conjugate match and the maximum
power transfer theorem.
______________

If this statement about the tank circuit being ~ a linear source is valid,
does that mean that any load-reflected power that appears across the output
terminals of the tx stops at the tank circuit, and never sees the
non-linear, non-matching Z of the active PA?

And if so, would that also mean that such a tx would not be prone to
producing r-f intermodulation components when external signals are fed back
into the tx from co-sited r-f systems?

Yet experience shows that this is not the case for ~closely spaced
interfering signals. The only mitigation for this for a PA with a tank
circuit is the rejection of that tank circuit to those off-freq, external
signals, and to the resulting IM products generated by mixing with the main
tx signal in the active (and non-linear) PA stage of that tx.

And the tank has VERY low rejection to load reflections of the signal
bandwidth to which it is tuned.

Also to be considered are the modern broadband (88-108MHz) FM broadcast
transmitters, which have no tank circuits, but except for some designs
incorporating balanced 3 dB hybrid combiners are affected by load
reflections about the same as a tx with a tuned tank circuit.

RF

Revisiting the Power Explanation
 

"Richard Fry wrote
(period = 1 cycle per ~491
feet of air-dielectric line).
_____________________

Sorry, make that 1 cycle == per MHz of bandwidth ==,
per ~491 feet of transmission line.

RF

Revisiting the Power Explanation
 

On Tue, 20 Mar 2007 19:19:26 -0500, "Richard Fry" wrote:

"Walter Maxwell" wrote
... I have explained many times that even though the PA source
upstream of the tank circuit is non-linear (and no one's saying it isn't),
the energy storage in the tank makes the output of the tank a linear
source, no matter what the shape of the current wave form may be
at the input. The output of the tank is proved linear because the
voltage/current ratio at the output is non-varying and the shape of
the voltage and current wave forms are essentially sine waves.
Consequently, the output circuit can be represented by a Thevenin
source that supports both a conjugate match and the maximum
power transfer theorem.
______________

If this statement about the tank circuit being ~ a linear source is valid,
does that mean that any load-reflected power that appears across the output
terminals of the tx stops at the tank circuit, and never sees the
non-linear, non-matching Z of the active PA?

Richard, my earlier treatise considers only tube-type PA's with pi-network output coupling circuits used in
the Amateur Service, such as the Kenwood TS-830S on which my measurements were made. It was not intended to
consider PA's used in the tv service. Sorry, I didn't make this distinction earlier.

And if so, would that also mean that such a tx would not be prone to
producing r-f intermodulation components when external signals are fed back
into the tx from co-sited r-f systems?

This issue is irrelevant, because the signals arriving from a co-sited system would not be coherent with the
local source signals, while load-reflected signals are coherent. The destructive and constructive interference
that occurs at the output of a correctly loaded and tuned PA requires coherence of the source and reflected
waves to achieve the total re-reflection of the reflected waves back into the direction toward the load.

Yet experience shows that this is not the case for ~closely spaced
interfering signals. The only mitigation for this for a PA with a tank
circuit is the rejection of that tank circuit to those off-freq, external
signals, and to the resulting IM products generated by mixing with the main
tx signal in the active (and non-linear) PA stage of that tx.

Again, Richard, this condition is irrelevant to the re-reflection of the waves reflected by the load, because
the relevant signals are not coherent.

And the tank has VERY low rejection to load reflections of the signal
bandwidth to which it is tuned.

This may be true for PAs with bandwidths wider than those occurring in ham tx. However, the destructive and
constructive interference between the reflected and source waves in a correctly loaded and tuned ham tx
results in total re-reflection of the reflected waves.

Also to be considered are the modern broadband (88-108MHz) FM broadcast
transmitters, which have no tank circuits, but except for some designs
incorporating balanced 3 dB hybrid combiners are affected by load
reflections about the same as a tx with a tuned tank circuit.

And still further, Richard, the FM transmitters you refer to above are not in the same category as those used
in tube rigs used by hams.

Incidentally, Richard, have you really reviewed the report of my TS-830S experiment?

Walt

Revisiting the Power Explanation
 

Cecil Moore wrote:
Richard Harrison wrote:
Terman says on page 96 of his 1955 opus:
"The reflected wave is identical with the incident wave except that it
is traveling toward the generator."

Gene needs to tell us how the TV modulation that
causes ghosting makes its predictable round trips
to the source and back without the aid of the
reverse traveling wave.

Cecil,

It is interesting that you can be so precise at times and so sloppy at
other times. I very carefully limited my discussion to steady state
conditions, which is what everyone is already talking about in this
case. You then conveniently inject modulation into the mix, completely
ignoring what I said.

Do the math and show us how my comment is in error. Add the two
traveling waves and see if you get the summation to be precisely a
standing wave plus a residual forward traveling wave. Go back and reread
your quoted references and try to figure out if anything I said is
different from your gurus.

73,
Gene
W4SZ

Revisiting the Power Explanation
 

"Walter Maxwell" wrote
(RF): And if so, would that also mean that such a tx would not be prone
to producing r-f intermodulation components when external signals
are fed back into the tx from co-sited r-f systems?

This issue is irrelevant, because the signals arriving from a co-sited
system would not be coherent with the local source signals, while load-
reflected signals are coherent. The destructive and constructive
interference that occurs at the output of a correctly loaded and tuned
PA requires coherence of the source and reflected waves to achieve
the total re-reflection of the reflected waves back into the direction
toward the load.

But even for coherent reflections, if the PA tank circuit has very low loss
for incident power (which it does), why does it not have ~ equally low loss
for load reflections of that power? Such would mean that load reflections
would pass through the tank to appear at the output element of the PA, where
they can add to its normal power dissipation.

Also, does not the result of combining the incident and reflected waves in
the tx depend in large part on the r-f phase of the reflection there
relative to the r-f phase of the incident wave? And the r-f phase of the
reflection is governed mostly by the number of electrical wavelengths of
transmission line between the load reflection and the plane of
interest/concern -- which is independent of how the tx has been
tuned/loaded.

If the ham transmitter designs that your paper applies to produce a total
re-reflection of reverse power seen at their output tank circuits, then
there would be no particular need for "VSWR foldback" circuits to protect
them. Yet I believe these circuits are fairly common in ham transmitters,
aren't they? They certainly are universal in modern AM/FM/TV broadcast
transmitters, and are the result of early field experience where PA tubes,
tx output networks, and the transmission line between the tx and the antenna
could arc over and/or melt when reflected power was sufficiently high.

RF

Revisiting the Power Explanation
 

On Mar 20, 3:43 pm, Cecil Moore wrote:
I understand what happens to the direction and
momentum in the reflected wave when it encounters
an impedance discontinuity at some distance from
the source, e.g. a Z0-match.

What happens to the direction and momentum in the
reflected wave when it encounters a non-dissipative
resistance at the source?

For some years now, you have been arguing the reality of 'reverse
power'. 'Reverse power' has served you well in that it appears
to offer reasonable explanation for some phenomena:
- 'forward power' minus 'reverse power' yields transferred power
- circulators
- TV ghosting
- dissipation of pulses in generators

But there are some challenges to the premise of 'reverse power':
- where does the 'reverse power' go?
- why does the change in dissipation of a generator when 'reverse
power' changes depend more on the design of the generator than
on the magnitude of the 'reverse power'?

In an attempt to resolve these, you have apparently done extensive
studies in optics looking for an explanation based on constructive
and destructive interference but are still left with the question you
posed above and others, like the one below from another of your
posts:

All one has to do to calculate the reflected power
dissipated in the source is to understand the constructive
and destructive interference occurring at the source
output terminal. THIS IS EASIER SAID THAN DONE. [emphasis mine]

Like myself, others have encountered difficulties with the premise
of 'reverse power'. But we have taken a different path to
enlightenment than yours; we have given up on the premise that
'reverse power' represents something that is real. To do this, we
have had to find alternative explanations to all the phenomena
listed above, but once this was done, life was good.

I would suggest that you try trodding this path. Make a list of
phenomena that you think are explained by 'reverse power'. For
each phenomena, explore the possibility of alternative explanations
that do not require 'reverse power'. When you have an explanation
for each, test the explanations against each other to ensure they
are self-consistent, then take the body of non-'reverse power'
explanations and compare it the body of 'reverse power' explanations.
Which is more complete? Which violates fewer fundamentals?

You have believed in 'reverse power' for so long that you will
probably find this path difficult. Make a conscious effort when
thinking about circulators, for example, not to give up because
it does not explain ghosting. Work out the solution to ghosting
later. Similarly, when working on steady-state examples, do not
confuse yourself with transients. Do those later. And when
exploring a phenomena using a hypothetical generator, do not
simply give up because it does not accurately model a real
transmitter. Much can be learned from the simplifications of
ideal voltage and current sources.

Those who have already trodden this path are, I am quite sure,
willing to assist you in finding the solutions, if you are willing
to learn, rather than tossing distractions into the discussion.
Save the other phenomena that trouble you for a later discussion.
Keep the discussion on track.

You can not lose if you take this path. In the best ending, you
end up with a coherent explanation for all the phenomena and can
give up on your search for solutions to the troubling issues posed
by 'reverse power' and the vanishing of the energy. But even if
you do not change your view you will have a better appreciation of
the alternative explanations and should be better able to partake
in debates on their correctness.

You could start by providing a list of phenomena for which you
think the reality of 'reverse power' is the only viable explanation
and offer a willingness to learn about alternative explanations.

....Keith

Revisiting the Power Explanation
 

Keith wrote:
"For some years now, you have been arguing the reality of "reverse
power".

For good reason. You feed a transmission line into an open circuit at
its far end, and the power arriving at the open has no where to go but
to return towards its generator. What happens at the generator upon
arrival of the power reflected from the mismatched load depends on the
vector values of incident and reflected waves as well as the impedance
of the generator.

Searching the net for "reflected r-f power" returned over 25,000
examples. Belief in reverse power is obviously common.

Best regards, Richard Harrison, KB5WZI

Revisiting the Power Explanation
 

On Mar 21, 12:08 pm, (Richard Harrison)
wrote:
Keith wrote:

"For some years now, you have been arguing the reality of "reverse
power".

For good reason. You feed a transmission line into an open circuit at
its far end, and the power arriving at the open has no where to go but
to return towards its generator. What happens at the generator upon
arrival of the power reflected from the mismatched load depends on the
vector values of incident and reflected waves as well as the impedance
of the generator.

Searching the net for "reflected r-f power" returned over 25,000
examples. Belief in reverse power is obviously common.

Best regards, Richard Harrison, KB5WZI

You are certainly correct; many people believe in reflected power,
though I've
always found that to be a poor basis for my own beliefs.

You have also provided the classic example where the numerology works
and 'reverse power' offers a tidy explanation. I am sure this neat
example is
the basis for many people's belief.

What drove me to look at alternate explanations for these kinds of
examples
was that the 'reverse power' explanation fails miserably when the
power
gets back to the generator. Having another explanation for this
classic
example lets one let go of 'reverse power' which solves the challenges
at the
generator end. When 'reverse power' is not real, the question of where
it
goes becomes irrelevant.

....Keith

Revisiting the Power Explanation
 

Keith Dysart wrote:

You are certainly correct; many people believe in reflected power,
though I've
always found that to be a poor basis for my own beliefs.

You have also provided the classic example where the numerology works
and 'reverse power' offers a tidy explanation. I am sure this neat
example is
the basis for many people's belief.

Belief has nothing to do with it. Observations suffice. If you have any
doubt that EM radiation can be reflected, just look in a mirror. Did you
need to 'believe' you saw your reflection to confirm your observation?

What drove me to look at alternate explanations for these kinds of
examples
was that the 'reverse power' explanation fails miserably when the
power
gets back to the generator.

Red Herring. There is no 'failure' in the accounting of reflected power.
The observations and numbers work out quite nicely.

Revisiting the Power Explanation
 

Keith wrote:
"Having another explanaton for this classic example lets one let go of
"reverse power" which solves the challenges at the generator end."

Bird says of its Model 43 Wattmeter: "Experience using the "Thruline"
Wattmeter for transmitter tune-up, antenna matching, etc. (i.e. on
operating problems), shows that the power ratio is as useful in practice
as the VSWR."

One can see reflected power disappear at the transmitter terminals as a
match is made to the transmitter load. That eliminates stress on the
transmitter from reverse power.

Reverse power is as real as its Bird Wattmeter indication.

Best regards, Richard Harrison, KB5WZI

Revisiting the Power Explanation
 

On Mar 21, 1:32 pm, Dan Bloomquist wrote:

Belief has nothing to do with it. Observations suffice. If you have any
doubt that EM radiation can be reflected, just look in a mirror. Did you
need to 'believe' you saw your reflection to confirm your observation?

I have yet to question the reflection of EM radiation, just the
existence of
"reverse power" in transmission lines.

Red Herring. There is no 'failure' in the accounting of reflected power.
The observations and numbers work out quite nicely.

A simple example that I can never make add up is a 50 Watt generator
with a 50 ohm output impedance, driving a 50 ohm line which is open at
the end. Using the "reverse power" explanation, 50 W of "forward
power"
from the generator is reflected at the open end, providing 50 W of
"reverse
power". Since the generator is matched to the line there is no
reflection
when this "reverse power" reaches the generator so it disappears into
the generator. If this is truly power, it must go somewhere else, be
dissipated, transformed into some other form or stored (based on the
conservation of energy principle). Where did it go?

Most correspondents agree that what happens depends on the design
of generator; dissipation either increases, decreases or stays the
same (compared to when the line was terminated in 50 Ohms and the
power going down the line is dissipated in the termination). This
does
not make an easy explanation for where that supposedly real power
goes. Of course, if it is not real power, then there is no issue,
which
leads one back to looking for explanations other than "reverse power".

....Keith

Revisiting the Power Explanation
 

On Mar 21, 3:06 pm, (Richard Harrison)
wrote:
Bird says of its Model 43 Wattmeter: "Experience using the "Thruline"
Wattmeter for transmitter tune-up, antenna matching, etc. (i.e. on
operating problems), shows that the power ratio is as useful in practice
as the VSWR."

One can see reflected power disappear at the transmitter terminals as a
match is made to the transmitter load. That eliminates stress on the
transmitter from reverse power.

I suggest that a more accurate description would read:
"One can see the indication on meter go to zero at the transmitter
terminals as the match is made to the transmitter load".

The scale on the meter could be labelled "furlongs per fortnight" and
this would still be true.

After exploring alternative explanations for the various phenomena,
the explorer will be ready to understand what a directional wattmeter
really measures (as opposed to what its meter scale claims to
indicate)
and truly understand what inferences can be correctly made from its
indications.

Reverse power is as real as its Bird Wattmeter indication.

I absolutely agree with this.

....Keith

Revisiting the Power Explanation
 

Keith Dysart wrote:

On Mar 21, 1:32 pm, Dan Bloomquist wrote:


Belief has nothing to do with it. Observations suffice. If you have any
doubt that EM radiation can be reflected, just look in a mirror. Did you
need to 'believe' you saw your reflection to confirm your observation?


I have yet to question the reflection of EM radiation, just the
existence of
"reverse power" in transmission lines.

Use of a TDR makes for a valid observation on the line.

Red Herring. There is no 'failure' in the accounting of reflected power.
The observations and numbers work out quite nicely.

A simple example that I can never make add up is a 50 Watt generator
with a 50 ohm output impedance, driving a 50 ohm line which is open at
the end. Using the "reverse power" explanation, 50 W of "forward
power"
from the generator is reflected at the open end, providing 50 W of
"reverse
power". Since the generator is matched to the line there is no
reflection
when this "reverse power" reaches the generator so it disappears into
the generator....

I explained this last week, albeit for a different reason. I'll paste:
***
Hi Richard,
He says it in the last sentence. But here is an example. Take a 50 ohm
thevinin source. Power off, it looks like 50 ohms back into it. Take a
second thevinin source to represent a reflection and drive 5 volts into
the first source. Now set your first source 180 degrees to the
reflection and drive forward 5 volts.

(s)-----/\/\/\--------(c)-----/\/\/\--------(r)

(s)source (c)connection (r)reflection. With (s) 180 degrees out of phase
from (r), (r) will see a short at (c). It is because of the power
generated at the source that the impedance into it can look purely
reactive. And, you can use 5 ohms with 1 volt at the source, (c) will
still look like a short to (r). The source resistance doesn't matter as
long as a 'match' is made.

And for the same reason, why the 50 ohm line doesn't look like 50 ohms
is because of reflected power. Drive an open quarter wave line and it
looks like a short because the reflected voltage is 180 degrees out from
the source.
***

If this is truly power, it must go somewhere else, be
dissipated, transformed into some other form or stored (based on the
conservation of energy principle). Where did it go?

The energy is sitting on the line. It didn't disappear. See all the
posts I made last week.


Most correspondents agree that what happens depends on the design
of generator;

Actually, it doesn't. The exception is minor and pointed out in the case
of a non linear source.

dissipation either increases, decreases or stays the
same (compared to when the line was terminated in 50 Ohms and the
power going down the line is dissipated in the termination). This
does
not make an easy explanation for where that supposedly real power
goes. Of course, if it is not real power, then there is no issue,
which
leads one back to looking for explanations other than "reverse power".

The mistake is in assuming the energy must disappear. It doesn't.

...Keith

Best, Dan.

Revisiting the Power Explanation
 

Keith Dysart wrote:

On Mar 21, 3:06 pm, (Richard Harrison)
wrote:

Bird says of its Model 43 Wattmeter: "Experience using the "Thruline"
Wattmeter for transmitter tune-up, antenna matching, etc. (i.e. on
operating problems), shows that the power ratio is as useful in practice
as the VSWR."

One can see reflected power disappear at the transmitter terminals as a
match is made to the transmitter load. That eliminates stress on the
transmitter from reverse power.

I suggest that a more accurate description would read:
"One can see the indication on meter go to zero at the transmitter
terminals as the match is made to the transmitter load".

Then, you have never matched with a reflection. Without the experience,
how can you make a claim? You have not made the observation yet you
claim what it 'should' be.

Revisiting the Power Explanation
 

"Keith Dysart" wrote in news:1174507951.363436.150330
@y66g2000hsf.googlegroups.com:

....
The scale on the meter could be labelled "furlongs per fortnight" and
this would still be true.

After exploring alternative explanations for the various phenomena,
the explorer will be ready to understand what a directional wattmeter
really measures (as opposed to what its meter scale claims to
indicate)
and truly understand what inferences can be correctly made from its
indications.

Keith,

I drafted an article exploring the operation of a Breune type directional
wattmeter, it is at http://www.vk1od.net/VSWR/VSWRMeter.htm . The Bird 43
responds in the same way, but from a different sampler construction.

The article gives a simple derivation of the meter response, and deals
with the legitimacy of scaling the instrument in Watts.

If one takes measurements with the instrument, it is true that the power
at a point is "forward power" less "reflected power", and the
manufacturer has scaled the instrument in Watts to facilitate that
calculation, but that does not imply that the value of "forward power" or
"reflected power" has any stand alone value, the ratio of the two is
meaningful, the difference of the two is meaningful, but one alone is
meaningless.

To illustrate the lack of stand-alone value of the "forward power"
reading, one could place two such instruments, one calibrated for 50 ohm
and another calibrated for 100 ohm in tandem at the tx, and then a load.
The two instruments will indicate different "forward power" and different
"reflected power".

Notwithstanding the fact that the "forward power" and "reflected power"
readings are each not of stand alone, the difference between "forward
power" and "reflected power" has meaning and will be the same for each
instrument.

I agree with you that a lack of understanding of the instrument can be
used to prop up bogus explanations and concepts, even leading to people
citing the Bird 43 user manual like it was a respected and authoritative
text.

Owen

Revisiting the Power Explanation
 

Owen Duffy wrote in
:

Notwithstanding the fact that the "forward power" and "reflected
power" readings are each not of stand alone, the difference between
"forward power" and "reflected power" has meaning and will be the same
for each instrument.

That reads better with the missing word supplied:

Notwithstanding the fact that the "forward power" and "reflected power"
readings are each not of stand alone meaning, the difference between
"forward power" and "reflected power" has meaning and will be the same for
each instrument.

Revisiting the Power Explanation
 

On Mar 21, 4:30 pm, Dan Bloomquist wrote:
Keith Dysart wrote:
On Mar 21, 3:06 pm, (Richard Harrison)
wrote:

Bird says of its Model 43 Wattmeter: "Experience using the "Thruline"
Wattmeter for transmitter tune-up, antenna matching, etc. (i.e. on
operating problems), shows that the power ratio is as useful in practice
as the VSWR."

One can see reflected power disappear at the transmitter terminals as a
match is made to the transmitter load. That eliminates stress on the
transmitter from reverse power.

I suggest that a more accurate description would read:
"One can see the indication on the meter go to zero at the transmitter
terminals as the match is made to the transmitter load".

Then, you have never matched with a reflection. Without the experience,
how can you make a claim? You have not made the observation yet you
claim what it 'should' be.

I may have misunderstood, but I thought that when Richard said "see
reflected power disappear" he was observing the Bird Wattmeter
mentioned
in his previous paragraph and watching its indication go to zero. If
this
is not what was meant, then I need elaboration.

Otherwise, I think I said the same as Richard in different (and,
arguably
more precise) words.

....Keith

Revisiting the Power Explanation
 

Would any poster in this thread who doesn't "believe in" reflected
power kindly explain how a transmission line can fail upstream of a
serious mismatch anywhere along the the length of that line. If that
doesn't result from the sum of forward and reflected voltage/current,
then (IYO) what is the reason such failures?

Don't think that this doesn't occur. I've seen it many times, and had
to find and replace the molten and arced-over components that
resulted.

RF

Revisiting the Power Explanation
 

Keith Dysart wrote:

On Mar 21, 4:30 pm, Dan Bloomquist wrote:

Keith Dysart wrote:

On Mar 21, 3:06 pm, (Richard Harrison)
wrote:

Bird says of its Model 43 Wattmeter: "Experience using the "Thruline"
Wattmeter for transmitter tune-up, antenna matching, etc. (i.e. on
operating problems), shows that the power ratio is as useful in practice
as the VSWR."

One can see reflected power disappear at the transmitter terminals as a
match is made to the transmitter load. That eliminates stress on the
transmitter from reverse power.

I suggest that a more accurate description would read:
"One can see the indication on the meter go to zero at the transmitter
terminals as the match is made to the transmitter load".

Then, you have never matched with a reflection. Without the experience,
how can you make a claim? You have not made the observation yet you
claim what it 'should' be.


I may have misunderstood, but I thought that when Richard said "see
reflected power disappear" he was observing the Bird Wattmeter
mentioned
in his previous paragraph and watching its indication go to zero. If
this
is not what was meant, then I need elaboration.

My mistake. You both said something that is not what happens. I will
assume you are looking for no reflection between a transmitter and a
transmatch. But the source to a transmission line is on the other side
of that transmatch. You will most certainly see a reflected wave if the
end of that transmission line is not terminated into purely 50 ohm load.

Otherwise, I think I said the same as Richard in different (and,
arguably
more precise) words.

I see that. But neither is the case. If you are matching a transmitter
to mis-matched line, the reflection does not go to zero. In fact, the
reflection is a function of the line and termination and is constant.
Nothing you do at the transmitter can change it.


...Keith

Best, Dan.

Revisiting the Power Explanation
 

"Richard Fry" wrote in news:1174511497.343920.155080
@e1g2000hsg.googlegroups.com:

Would any poster in this thread who doesn't "believe in" reflected
power kindly explain how a transmission line can fail upstream of a
serious mismatch anywhere along the the length of that line. If that
doesn't result from the sum of forward and reflected voltage/current,
then (IYO) what is the reason such failures?

Without making any admissions about my beliefs...

A transmission line with mismatched load can be described in terms of
travelling waves, and the voltage and current at a point on the line can
be calculated from the forward and reflected waves.

The voltage at the point may be higher than under matched conditions for
the same load power, and that may cause insulation breakdown.

The current at the point may be higher than under matched conditions for
the same load power, and that would cause higher loss in conductors and
may result in damage.

Don't think that this doesn't occur. I've seen it many times, and had
to find and replace the molten and arced-over components that
resulted.

None of these explanations require designating "reflected power" at a
point, or implying that it is the energy in "reflected power" that is
totally and solely responsible for the physical damage.

Owen

Revisiting the Power Explanation
 

On Mar 21, 5:11 pm, "Richard Fry" wrote:
Would any poster in this thread who doesn't "believe in" reflected
power kindly explain how a transmission line can fail upstream of a
serious mismatch anywhere along the the length of that line. If that
doesn't result from the sum of forward and reflected voltage/current,
then (IYO) what is the reason such failures?

Don't think that this doesn't occur. I've seen it many times, and had
to find and replace the molten and arced-over components that
resulted.

RF

You pose a phonomenon that should be added to the list that
needs to be explained without the use of "reverse power".

And you have done an excellent job of doing so by providing
an explanation that refers only to forward and reflected
voltage and current. Not a mention of "reverse power" in
the explanation..

....Keith

Revisiting the Power Explanation
 

Keith Dysart wrote:

You pose a phonomenon that should be added to the list that
needs to be explained without the use of "reverse power".

Me thinks you are trolling and have no interest in an understanding.

Revisiting the Power Explanation
 

"Owen Duffy" wrote
None of these explanations require designating "reflected power"
at a point, or implying that it is the energy in "reflected power"
that is totally and solely responsible for the physical damage.
___________

I guess you are relying on the fact that there will be no reflected r-f
voltage/
current if there is no incident voltage/current? And no argument, there.

But of course, it is the vector sum of ALL of these that may cause the
transmission line/network/tx failure(s) mentioned in my relevant posts
in this thread.

And so that does NOT prove that reflected power/voltage/current
does not exist, or is unimportant in an r-f system design.

The specifications of a transmission line or other r-f network or circuit
can be chosen with due engineering care to be rated for a defined incident
power applied to a load with a given mismatch to a specific Zo, and with
respect to the carrier frequency, the modulation thereon, the ambient air
temperature/pressure, solar illumination, line pressurization, and other
operating parameters.

These realities are commonly recogniz(s)ed and incorporated by most
commercial designers/evaluators of r-f transmission systems, and as a result
pose no significant problems to them and/or their clients.

But none of this means that r-f reflections do not, may not, or can not
exist -- whether in "ham" systems, or otherwise.

RF

PS: Please edit my email address in replies here so that
it can't accurately be picked up by spammers. I get enough
spam already. Gracias.

Revisiting the Power Explanation
 

On Mar 21, 5:24 pm, Dan Bloomquist wrote:
Keith Dysart wrote:
On Mar 21, 4:30 pm, Dan Bloomquist wrote:

Keith Dysart wrote:

On Mar 21, 3:06 pm, (Richard Harrison)
wrote:

Bird says of its Model 43 Wattmeter: "Experience using the "Thruline"
Wattmeter for transmitter tune-up, antenna matching, etc. (i.e. on
operating problems), shows that the power ratio is as useful in practice
as the VSWR."

One can see reflected power disappear at the transmitter terminals as a
match is made to the transmitter load. That eliminates stress on the
transmitter from reverse power.

I suggest that a more accurate description would read:
"One can see the indication on the meter go to zero at the transmitter
terminals as the match is made to the transmitter load".

Then, you have never matched with a reflection. Without the experience,
how can you make a claim? You have not made the observation yet you
claim what it 'should' be.

I may have misunderstood, but I thought that when Richard said "see
reflected power disappear" he was observing the Bird Wattmeter
mentioned
in his previous paragraph and watching its indication go to zero. If
this
is not what was meant, then I need elaboration.

My mistake. You both said something that is not what happens. I will
assume you are looking for no reflection between a transmitter and a
transmatch. But the source to a transmission line is on the other side
of that transmatch. You will most certainly see a reflected wave if the
end of that transmission line is not terminated into purely 50 ohm load.

Otherwise, I think I said the same as Richard in different (and,
arguably
more precise) words.

I see that. But neither is the case. If you are matching a transmitter
to mis-matched line, the reflection does not go to zero. In fact, the
reflection is a function of the line and termination and is constant.
Nothing you do at the transmitter can change it.



...Keith

Best, Dan

I agree with what you say.

I had made the leap that Richard's configuration was transmitter,
Bird, matching
device as that seemed to be the only way that an adjustment could
bring
the meter on the Bird to zero. If this was not the intended
configuration
then I am completely confused and Richard will need to clarify his
intent.

....Keith

Revisiting the Power Explanation
 

Owen Duffy wrote:
Ah, but that is USENET!

Yep, Love it or leave it. :-)

No one has demonstrated that using equivalent impedances etc is not a
valid analysis of the steady state behaviour.

Negative assertions are usually impossible to prove.
The onus of proof is upon the ones who assert that
reflected waves cease to exist during steady-state.
The distributed network reflection model has yielded
valid results for a century or so. Ramo and Whinnery
go so far as to talk about the forward power flow
vector and the reflected power flow vector. People
trying to discredit that model just haven't accomplished
their goal.
--
73, Cecil http://www.w5dxp.com

Revisiting the Power Explanation
 

Gene Fuller wrote:
It is interesting that you can be so precise at times and so sloppy at
other times. I very carefully limited my discussion to steady state
conditions, which is what everyone is already talking about in this
case. You then conveniently inject modulation into the mix, completely
ignoring what I said.

*Every* real world system has noise modulation
that can be tracked through the system riding on
the forward and reflected traveling waves. Thus
steady-state is never reached in reality and your
argument is therefore just a mind game.
--
73, Cecil http://www.w5dxp.com

Revisiting the Power Explanation
 

Keith wrote:
For some years now, you have been arguing the reality of 'reverse
power'.

Nope, for the last few years I have been arguing the
reality of a reverse or reflected EM energy wave. Energy
is what moves and is the essence of an EM wave moving
at the speed of light. All I am arguing is the validity
of the distributed network reflection model, something
that has stood the test of time for a century or so.

But there are some challenges to the premise of 'reverse power':
- where does the 'reverse power' go?
- why does the change in dissipation of a generator when 'reverse
power' changes depend more on the design of the generator than
on the magnitude of the 'reverse power'?

Reflected energy waves obey the principles of conservation
of energy and superposition some of which is discussed in
my WorldRadio energy article at:

http://www.w5dxp.com/energy.htm

I would suggest that you try trodding this path. Make a list of
phenomena that you think are explained by 'reverse power'.

Actually, "reflected energy" rather than "reverse power".
Here is very close to an experiment we did at Texas A&M
during the 50's. We observed the ghosting and the professor
explained reflected energy waves to us.

TVSG-----1000 feet 450 ohm ladder-line---75 ohm TV RCVR

If the TV Signal Generator is not equipped with a circulator
to get rid of the reflected energy wave, ghosts will appear on
the TV RCVR. The ghosts are exactly where they should be if
reflected wave energy exists. How would you explain the
ghosting?

You could start by providing a list of phenomena for which you
think the reality of 'reverse power' is the only viable explanation
and offer a willingness to learn about alternative explanations.

Please see above. And please abandon the words, "reverse
power" in favor of reverse or reflected EM energy wave.
--
73, Cecil http://www.w5dxp.com

Revisiting the Power Explanation
 

Richard Harrison wrote:
Searching the net for "reflected r-f power" returned over 25,000
examples. Belief in reverse power is obviously common.

Oh yeah, I forgot to tell Keith that I'm not the only
one who believes in the validity of reflected energy.
In fact, I see it every time I look in the mirror.

Also HP Ap Note 95-1 has some interesting things to
say, e.g. "|a2|^2 = Power reflected from the load."
--
73, Cecil http://www.w5dxp.com