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

Cecil Moore wrote in
et:

Owen Duffy wrote:
Cecil Moore wrote in
EM wave energy necessarily travels at the speed of light.
There is exactly the amount of EM wave energy contained
in a transmission line to support the forward power and
reflected power.

You are not suggesting that the energy contained in a transmission
line in the steady state in the general case is constant, are you?

Obviously, a leading question. :-) I'm not talking
about instantaneous values here. All my statements
apply only to values averaged over an integer
number of RF cycles in one second.

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.

Owen

Cecil Moore wrote:


It was Gene who first pointed out the difference
between a traveling wave and a standing wave. Now
he says there is no difference.


Cecil,

Utter nonsense. I have never said any such thing.

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. It is purely a matter of mathematical convenience. There is
no underlying hidden physics available from trying to look at only one
of the traveling wave components. If you sort out an individual
component then the standing wave is no longer there.

ad hominem Your debating style is a bit rough, but it is clear from
this thread that others have observed your tricks. /ad hominem

73,
Gene
W4SZ

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

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".
--
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

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.
--
73, Cecil http://www.w5dxp.com

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

My dictionary defines reflected power as:
"The power flowing back to the generator from the load."

Maximum power theorem is defined as:
"The maximum power will be absorbed by one network from another joined
to it at two terminals, when the impedance of the receiving network is
varied, if the impedances (looking into the two networks at the
junction) are conjugates of each other."

Clearly a generator (transmitter) connected to a load through a lossless
line sees Zo of the line as its load until the instant that reflected
power returns to the generator from the load.
Suppose the round-trip delay of the line makes the reflected voltage
exactly in phase with the transmitter output. further suppose the
reflection was total so that the reflected voltage exactly equals the
transmitter output. In this special case, we might as well be connecting
identical battery cells in parallel. No current is going to flow. The
generator is seeing infinite impedance.

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