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

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

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

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

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.

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

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.

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

Then you are certainly engaging in the proverbial Red Herring.

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?

This is a lot like the 1/2WL W7EL example in his food for
thought articles. The generator is *NOT* matched to the line
as it sees an open circuit and cannot continue to stuff 50
watts into the open circuit. The generator is as mismatched
as it can possibly be. The reflected wave also sees that open
circuit and is 100% reflected. Since the generator is not
delivering any power and there is a forward power and a
reflected power, the reflected power is supplying the
forward power. Anything else violates the conservation
of energy principle.

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".

Any level of interference is possible depending upon the
phase angle between the forward E-field and the reflected
E-field. All this is explained in "Optics" by Hecht which
some people have apparently avoided reading/understanding.
Optical physicists solved this problem a century ago. They
don't have the luxury of dealing with voltages and currents
and are forced to deal with power densities. You should
try trodding their paths and enlightening yourself.
--
73, Cecil http://www.w5dxp.com

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

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