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.

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, 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

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

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:

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.

"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

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.

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

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