Walter Maxwell wrote:
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. 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.

One can illustrate the destructive and constructive
interference with a solid-state transmitter and
no tuner. Consider the following example using
S-parameter terms.

100W--50 ohm line--+--1/2WL 300 ohm line--50 ohms
a1-- --a2
--b1 b2--

Since there is zero reflected power on the 50 ohm
line, we know that "total destructive interference"
(as described by Hecht in "Optics", 4th edition, page
388) exists toward the source at point '+'.
s11 = (300-50)/(300+50) = 0.7143 = -s12
b1 = (s11)(a1) + (s12)(a2) = 0

Note that given a1, s11, and s12, we can calculate the
magnitude and phase of a2 needed to make b1=0. That
is the Z0-match condition.

The conservation of energy principle says that, (in
a transmission line with only two directions) "total
constructive interference" must exist in the opposite
direction to the "total destructive interference" and
that they must be of equal magnitudes. That tells us
what *must* happen to the energy associated with the
a2 reflected wave.

All of the energy incident upon point '+' from both
directions, |a1|^2 + |a2|^2, is directed toward the
load by the interference patterns at the Z0-match
point '+'. We hams commonly refer to that condition
as being 100% re-reflected.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
All of the energy incident upon point '+' from both
directions, |a1|^2 + |a2|^2, is directed toward the
load by the interference patterns at the Z0-match
point '+'. We hams commonly refer to that condition
as being 100% re-reflected.

The above is true in the special case of a Z0-match.
In general, |a1|^2 + |a2|^2 = |b1|^2 + |b2|^2
and since |b1|^2 = 0, the above expression is
correct.

*Quoting from HP Ap Note 95-1*:

|a1|^2 = Power incident on the input of the network
(i.e. Forward power on the 50 ohm line)

|a2|^2 = Power reflected from the load
(i.e. Reflected power on the 300 ohm line)

|b1|^2 = Power reflected from the input port of the network
(i.e. Reflected power on the 50 ohm line)

|b2|^2 = Power incident on the load
(i.e. Forward power on the 300 ohm line)

end quote from HP Ap Note 95-1
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote in
:

....
s11 = (300-50)/(300+50) = 0.7143 = -s12
b1 = (s11)(a1) + (s12)(a2) = 0

Cecil,

I see you are back to using S parameters to disguise the fact you are using
about Vf and Vr in trying to support your "power wave" explanation of what
happens on the transmission line.

S parameters are ratios of Vf and Vr.

Owen

Owen Duffy wrote:
I see you are back to using S parameters to disguise the fact you are using
about Vf and Vr in trying to support your "power wave" explanation of what
happens on the transmission line.

Others use the term "power wave", Owen, but *I DO NOT*
so please stop accusing me of something of which I am
not guilty. I use the term "EM RF energy wave" for
the traveling waves under discussion.

When anyone can prove that RF energy waves don't exist
or are not associated with EM energy or don't move at
the speed of light, I will retire from the argument.
Good luck on that one.

S parameters are ratios of Vf and Vr.

Exactly! No disguise intended - it's just additional
support from the well respected field of S-parameter
analysis for the distributed network wave reflection
model. The only difference is that the S-parameter
Vf and Vr values are normalized to Z0 so when they
are squared they indeed do yield watts.

Your tone seems to reject the S-Parameter analysis
as a valid model of reality. Any model that has to
resort to rejecting the S-Parameter analysis as well
as the distributed network wave reflection model is
certainly suspect. Did you ever see the movie, "One
Bridge Too Far"? This "reflected wave energy doesn't
exist" argument reminds me of that movie.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote in
:

Your tone seems to reject the S-Parameter analysis
as a valid model of reality. Any model that has to

Not at all.

S parameters are Vf and Vr based and when properly applied will produce
exactly the same analysis outcome.

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.

A quote from HP (which you seem to respect):

===quote
Notice that the square of the magnitude of these
new variables has the dimension of power. |a1|^2
can then be thought of as the incident power on
port one; |b1|^2 as power reflected from port one.
These new waves can be called traveling power
waves rather than traveling voltage waves.
Throughout this seminar, we will simply refer to
these waves as traveling waves.
===equote

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

Owen

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

Cecil, W5DXP wrote:
"Others use the term 'power wave', but I DO NOT, so please stop accusing
me of something I am not guilty."

Power waves are respectable but a writer chooses his own words.

Searching the web on topic: "power reflection on mismatched line"
yielded 12,778 hits. First two were from the physics department of the
University of Queensland in Australia. No qualms about the word "power"
are shown and sample problems are worked. Here is one statement: "Note
that the power reflection coefficient is equal to the square of the
voltage (or current) coefficient because forward or reflected waves are
in rhe same impedance."

Remarkable or not, that is the seesnce of what the Bird Electronic
Corporation says in instructions for its "Thruline Wattmeter".

Power is acceptable and accepted. Why avoid the term?

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Power is acceptable and accepted. Why avoid the term?

Jim Kelley, AC6XG, has convinced me to make the
distinction between the nature of EM energy and
the nature of EM power. Power is what exists at
a point or plane. Energy is what is moving past
the point or through the plane. Reflected power
is measured at a point. Reflected energy is
what is doing the moving past that point.

In addition, there's the difference in definitions
between the fields of RF engineering and the field
of physics. In physics, zero work implies zero power.

I am not avoiding power. I am avoiding "power waves"
and "power flow". The dimensions of power flowing past
a point would be watts/second. I don't know what physical
quantity that would represent.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Richard Harrison wrote:
Power is acceptable and accepted. Why avoid the term?

Jim Kelley, AC6XG, has convinced me to make the
distinction between the nature of EM energy and
the nature of EM power. Power is what exists at
a point or plane. Energy is what is moving past
the point or through the plane. Reflected power
is measured at a point. Reflected energy is
what is doing the moving past that point.

In addition, there's the difference in definitions
between the fields of RF engineering and the field
of physics. In physics, zero work implies zero power.

I am not avoiding power. I am avoiding "power waves"
and "power flow". The dimensions of power flowing past
a point would be watts/second. I don't know what physical
quantity that would represent.

Cecil,

Utter nonsense. Jim was pulling your chain, and I guess you fell for it.

I have been a professional physicist for nearly 40 years. Real
physicists fully understand the difference between power as work and
power as energy transport. Both definitions are used as needed. I would
hazard a guess that most engineers understand and use both definitions
as well.

All of your ramblings about the difference between energy and power, as
well as joules and watts, add nothing but noise to the discussion. It is
highly likely that everyone reading this group understands the concept
of time.

73,
Gene
W4SZ

Gene Fuller, W4SZ wrote:
"Utter nonsense."

Cecil knows as well as anybody the difference between energy and power,
Power is the rate of doing work. The electrical unit is the watt
(joule/second). It is also the rate of transmission from source to load.

A wattmeter keeps track of the rate of energy flow, and the watt-hour
meter measures the integral of active power during the integration
interval.

The power company bills you for the energy consumed during an interval
determined by successive watt-hour meter readings.

Best regards, Richard Harrison, KB5WZI