On Wed, 26 May 2004 11:44:00 -0500, "Steve Nosko"
wrote:

I think "superposition" is ther wrong term for this. If I could spell
reciprocity, I'd say that it is a better word.
Digression, though minor: Superposition refers typically, to the
application of two signals to a circuit and the resulting response being the
sum of the individual responses. no?

No/Yes. The "two" signals are those I described, the one from the
source as source and the one from load as source. This is the
convention of Circuit Analysis by Mesh or Nodes. Kirchhoff mandates
all voltages will sum to zero. The summing is a solution of
simultaneous equations - Superposition.

Now some meat I'd like to pursue...

...a 500 Ohm Source...you will never launch much power into a 50 Ohm
system because it would immediately hit a reflective interface at the
antenna connector.

There's a question I see here as to wheather the power was "launched" in
the first place and this may be part of the assumption (or set thereof)
which (my gut feel says) leads the logic astray.

It was an aside (a stage whisper).

This means that a 500 Ohm source, when confronted
by power going towards it from a 50 Ohm system will reflect most of
that power (but how did we get this power into the system in the first
place - Karma?) This, by design, will never happen in any transistor
ham rig built in the last quarter century.

I think this is true...BUT let's ask this same question of a 5.0 ohm
source?? How would you carry this through Richard C? I submit that THIS
source CAN launch significant power down the line.

And here we come to issues of initial conditions and their variation
to force a conclusion. Namely, the unstated condition is how much
voltage is available? SWR is the diagnosis, and absorption of power
is the issue. Launching of power also suffers from the same
condition, but it would be well enough to examine the reflection
first. Launching problems is a sidebar.

The answer is the transmitter source Z is 50 Ohms at rated power.

OK, so now I see you are of the "Zs=50 ohms" camp.

I have measured such things professionally and certified such facts as
accurate with a chain of references back to the National Bureau of
Standards. Such is my camp.

If a watt of power is chooglin' down the line toward it, that 50 Ohms is
going to dissipate into a watt worth of calories. This can be argued
with wave mechanics, or lumped circuit equivalents - doesn't matter
because it's all the same calories.

All ok with me _IF_ Zs=50. I'm not convinced however. I have to think
more about the modern broad-band transistor PA to have an strongly arguable
opinion on this concept.

It is a convention of design that is covered in many design texts.
Academe takes this (Zs=50) for granted so much so that it is rarely
discussed. Even here I have references (Academic) that make this
point explicit and I have offered them here in debate.

what do we need tuners for?

I think the answer here is that if the transmitter can take the strange
impedance it sees, then it isn't needed. Like Hanks 30L1 that, however,
couldn't take it very well.

However, this is not an answer to the question.

Furthermore, there is an implicit assumption here in your reasoning
which I believe is key and leading to some error. There is an unspoken
assumption that the power which makes it to the antenna after all the "
round-and-round until the antenna finally radiates it" is the FULL output
and I believe it AIN'T.

As I have never stated this, you have to answer for the conflict that
follows.

It is that little dribble that made it into the
line in the first place. a.k.a. the Tx is not generating the full output.
I think this assumption is causing much trouble.

This begs the question: What is the full output? A battery sitting on
the shelf is not generating its full output is a simple example, but
does not tell us what that full output may be. This is the problem of
definition by negatives.

It is not generating:
1W
nor
10V
nor
100°C
nor
1 H.P.

Was it ever capable of those generations in the first place? Under
what conditions? Saying what is "not" has no useful information here.

If we are discussing what happens to power impinging upon the source,
it should be obvious that if that power is OUT OF PHASE trouble
follows in the form of currents. If that power is IN PHASE trouble
follows in the form of potentials. Trouble is proportional to the
degree of mismatch. Trouble arrives through the model of waves,
trouble resides in the model of lumped equivalent circuits. It is the
same trouble either way in the form of heat. Choose your poison
because equipment manufacturers have built-in foldback mechanisms and
advise you to use a tuner for good reason.

Unless, of course, I have been smoking the wrong brand.

It will be available over the counter in British Columbia soon.

73's
Richard Clark, KB7QHC