Revisiting the Power Explanation
 

Owen Duffy wrote:
It is the application of S parameters in the "power flow analysis" that
is a reach, it might be convenient, but it does not legitmise the
argument that forward and reflected "power waves" exist separately.

Nth reminder to you: Please stop implying something
I didn't say. I have said that forward and reflected RF
traveling energy waves exist separately. If you can find
an example of me using the term "power wave" in the 21st
century, I will send you a $100 bill.

A quote from HP (which you seem to respect):
Throughout this seminar, we will simply refer to
these waves as traveling waves.

There is a difference between "can then be thought of as..." and
"are...".

EXACTLY! You and I are generally in agreement except
when you accuse me of nonsense like "power waves".
Please cease and desist! I simply refer to these
waves as traveling energy waves, NOT POWER WAVES!
--
73, Cecil http://www.w5dxp.com

Revisiting the Power Explanation
 

Cecil Moore wrote in
:

Owen Duffy wrote:
This gets confusing. You are talking about "the amount of EM wave
energy contained in a transmission line" and now you qualify it with
"values averaged over an integer number of RF cycles in one second".
Average energy over time is POWER... are you talking about power and
foxing us by calling it energy. I am confused.

I have been convinced by Jim, AC6XG, to abandon the word
"power" because of the difference in definitions between
the field of physics and the field of RF engineering.

Jim would argue with you and say that average energy over
time is NOT necessarily POWER and is only power if actual
work is done which, of course, is not done by a reflected
wave.

So you need to go off and argue with Jim over the
definition of "power". Instead of talking about power,
Jim has convinced me to talk about watts or joules/sec
which he says are not necessarily power. The confusion
comes from the field of physics, not from me. While you
are talking to Jim, get him to explain the definition
of "transfer".

A neat diversion from the issue re the "amount of energy" qualified later
as a average over time which is a different quantity, Joules vs Watts to
many of us.

The fact is that the energy stored in a transmission line in the steady
state is in the general case, a time variable, and you cannot state the
energy (in joules) at a point in time knowing only forward and reflected
power and the one way propagation time.

So Cecil,

Is it all about semantics? Is the lack of a shared language the cause of
difficulty understanding your concepts. You wouldn't be alone, Art
experiences the same difficulties with convention.

Owen

Revisiting the Power Explanation
 

On Thu, 22 Mar 2007 15:55:40 GMT, Walter Maxwell
wrote:

On Wed, 21 Mar 2007 08:18:14 -0500, "Richard Fry" wrote:

"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.

Hi Walt,

It is not irrelevant, merely illustrative of the concept of reflection
that is consistent with a coherent source.

Your points of phase are the sine non quo to the discussion, but all
too often arguers only take the half of the 360 degrees available to
argue a total solution. Even more often, they take only one or two
degrees of the 360.

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.

This is the symmetry of the illustration of external signals. You
used external signals yourself as part of your case study; hence the
relevance has been made by you.

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.

And we return to the sine non quo for the discussion: phase.

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

Richard, your statement above begs the question, "Are you aware of the phase relationships between forward and
reflected voltages and between forward and reflected currrents that accomplish the impedance-matching effect
at matching points such as with stub matching and also with antenna tuners?

It seems he is on the face of it, doesn't it? Afterall, he is quite
explicit to this in the statement you are challenging.

When the matching is accomplished the phase relationship between the foward and reflected voltages can become
either 0° or 180°, resulting in a total re-reflection of the voltage. If the resultant voltage is 0°, then the
resultant current is 180°, thus voltage sees a virtual open circuit and the current sees a virtual short
circuit. The result is that the reflected voltage and current are totally re-reflected IN PHASE with the
source voltage and current. This is the reason the forward power in the line is greater than the source power
when the line is mismatched at the load, but where the matching device has re-reflected the reflected waves.

Nothing here contradicts anything either of you have to say.

This phenomenon occurs in all tube transmitters in the ham world when the tank circuit is adjusted for
delivering all available power at a given drive level.

This introduces the two concepts of the "need for match" and the
"match obtained." They are related only through an action that spans
from one condition to the other. They do not describe the same
condition, otherwise no one would ever need to perform the match:

When this condition occurs the adjustment of the
pi-network has caused the relationship between the forward and reflected voltages to be either 0° or 180° and
vice versa for currents, as explained above. When this condition occurs, destructive interference between the
forward and reflected voltages, as well as between the forward and reflected currents, causes the reflected
voltage and current to cancel. However, due to the conservation of energy, the reflected voltage and current
cannot just disappear, so the resulting constructive interference following immediately, causes the reflected
voltage and current to be reversed in direction, now going in the foward direction along with and in phase
with the forward voltage and current.

If a tree were to fall onto the antenna, a new mismatch would occur.
Would the transmitter faithfully meet the expectations of the Ham
unaware of the accident? No, reflected (0-179 degrees) energy would
undoubtedly offer a 50% chance of excitement in the shack. The
consequences of dissipation would be quite evident on that occasion.
For the other 180 (180-359) degrees of benign combination; then
perhaps not.

In transmitters with tubes and a pi-network output coupling circuit there is no 'fold back' circuitry to
protect the amp, because none is needed, due to the total re-reflection of the reflected power.

That would more probably be due to cost averse buying habits of the
Amateur community, and the explicit assumption of risk by them to
react appropriately in the face of mismatch. Tubes were far more
resilient to these incidents than transistors of yore.

It is only in
solid-state transmitters that have no circuitry to achieve destructive and constructive interference that
requires fold back to protect the output transistors.

They too have access to the services of a transmatch that is probably
more flexible than the tubes' final. If they didn't use a tuner, then
the foldback would render many opportunistic antennas as useless.
Again, as a cost item, this solution (fold-back) is dirt cheap and was
driven by the market economies of a more onerous and costly repair
through a lengthy bench time to replace the transistor (which has an
exceedingly high probability of a quicker failure for a poor job).

73's
Richard Clark, KB7QHC

Revisiting the Power Explanation
 

Owen Duffy wrote:
The fact is that the energy stored in a transmission line in the steady
state is in the general case, a time variable, and you cannot state the
energy (in joules) at a point in time knowing only forward and reflected
power and the one way propagation time.

The time-averaged energy stored in a transmission line
doesn't vary with time (by definition) unless something
changes.

If the forward and reflected powers are based on fixed
RMS values of voltage and current with fixed sources and
loads, then certainly, time-averaged energy values can be
calculated. That's the nature of *irradiance* in optics
where instantaneous values are impossible to measure. The
Power Flow Vector is analogous to irradiance.

Is it all about semantics? Is the lack of a shared language the cause of
difficulty understanding your concepts.

No, the basic problem is that you keep accusing me of
saying something I never said. I have never used the
term "power wave" except in postings like this one.
I have no idea what is the definition of "power wave".

How it feels:

It feels to me like you are one of a number of people
willing to reject the basic principles of physics in
order to mount an argument with me or anyone else
who have been convinced by those laws of physics that
reflected energy waves exist in reality - you know,
the ones you actually see when looking in a mirror?
--
73, Cecil http://www.w5dxp.com

Revisiting the Power Explanation
 

Cecil Moore wrote:
Gene Fuller wrote:
Utter nonsense. I have never said any such thing.

Yes, you did, in the part that you deleted. Here it
is again:

Gene Fuller, W4SZ wrote:
In a standing wave antenna problem, such as the one you describe,
there is no remaining phase information. Any specific phase
characteristics of the traveling waves died out when the startup
transients died out.

Phase is gone. Kaput. Vanished. Cannot be recovered. Never to be
seen again.

What I *did* say, and it is still true today, is that there is no
difference between a standing wave and its *constituent* traveling
wave components.

The constituent traveling wave components possess changing
phase. The standing wave doesn't possess changing phase.
You are contradicting yourself.

Cecil,

Sorry, I thought that English was your native tongue. Would you like me
to try to translate into another preferred language?

Hint: I stand by everything I have said in the quotes above. No
contradictions at all.

73,
Gene
W4SZ

Revisiting the Power Explanation
 

Gene Fuller wrote:
Sorry, I thought that English was your native tongue. Would you like me
to try to translate into another preferred language?

Translation: I've been caught red-handed by
my own American English words. Maybe converting
to an obscure foreign language would give me more
wiggle room.
--
73, Cecil http://www.w5dxp.com

Revisiting the Power Explanation
 

"Owen Duffy" wrote
So Cecil,
Is it all about semantics? Is the lack of a shared language the cause of
difficulty understanding your concepts. You wouldn't be alone, Art
experiences the same difficulties with convention.
Owen

Great deduction, Owen! Perhaps Art would benefit from a copy
of "Gaussian Optics, with Definitions". Thinkiing about that makes
me wonder....if Cecil were to feed a one-second long transmission
line, 50 Zo, terminated by Art's Gaussian Array, how long before
the (power)(energy)(whatever) starts sloshing ??

Mike W5CHR

Revisiting the Power Explanation
 

Mike Lucas wrote:
"Owen Duffy" wrote
So Cecil,
Is it all about semantics? Is the lack of a shared language the cause of
difficulty understanding your concepts. You wouldn't be alone, Art
experiences the same difficulties with convention.

Great deduction, Owen!

Unfortunately, Owen may be the one with the semantic problem.
He has quoted me as uttering the phase, "power wave", which
I have never, to the best of my memory, ever uttered. A
$100 bill is awaiting proof of his assertions.
--
73, Cecil http://www.w5dxp.com

Revisiting the Power Explanation
 

On Mar 22, 12:31 pm, (Richard Harrison)
wrote:

What is the generator load that extracts maximum power from a
transmitter? A conjugately matched load, of course. To determine the
impedance of a transmitter, one only needs to find the load which
extracts maximum power. The transmitter impedance is its conjugate.

Best regards, Richard Harrison, KB5WZI

We have a new signal generator here at the Labs, but it came without
any documentation. We've been hoping to find out more about it, and
your suggestion gave us a clue for a test to try. We have a limited
set of loads, only from 40 to 60 ohms, but we can add some known
reactance in series with that. When we put an accurate 50 ohm load on
the generator, we measured exactly 1 watt with our accurate RF power
meter. When we changed the load to 40 ohms, the power went up to
1.238 watts, and with a 60 ohm load, it was .839 watts. When we add
reactance, either capacitive or inductive, the power goes down, so
we're pretty sure the generator output doesn't look reactive. Beaker
is having a little trouble with the math on this one. Could you help
him out? What sort of output impedance does this generator have?

Oh, and we thought to do another experiment. While the generator was
operating, we sent a short burst of RF down a 50 ohm transmission line
to the generator's output. Because the power measurements seem to say
the generator's output resistance is very low, we thought we would see
a return pulse, delayed by the round-trip time down the 15 meters of
high-quality cable. But we didn't see any echo. What could be going
on? We double-checked everything, and even looked into the line next
to the generator with a high impedance probe. We can see the burst
going in there, but still nothing comes back.

From the labs,
Dr. Honeydew

Revisiting the Power Explanation
 

"Dr. Honeydew" wrote in
oups.com:

On Mar 22, 12:31 pm, (Richard Harrison)
wrote:

What is the generator load that extracts maximum power from a
transmitter? A conjugately matched load, of course. To determine the
impedance of a transmitter, one only needs to find the load which
extracts maximum power. The transmitter impedance is its conjugate.

Best regards, Richard Harrison, KB5WZI

We have a new signal generator here at the Labs, but it came without
any documentation. We've been hoping to find out more about it, and
your suggestion gave us a clue for a test to try. We have a limited

If you have a suspicion that the generator might be 50 ohms, and you have
a 50 ohm load, then the output voltage should fall by 6.02dB when the
nominal load is connected (compared to o/c).

One of the simple tests that is often used to verify that a generator is
loaded properly is that adding a second nominal load in parallel reduces
terminal voltage by 3.52dB. This test is often easy to perform, use a
power meter for the first termination, watch the reduction in indicated
power when a double termination is applied. Be mindful that transmission
line lengths need to be short wrt operating frequency.

Some numbers:

1st termination reduces output by 6.02dB;
2nd termination reduces output by 3.52dB;
3rd termination reduces output by 2.50dB;

Owen
....