Your use of "Dr. Best's conventions" only muddles the matter -- neither
I nor probably any of the other readers have any idea what this is. In
any event, the numbers you produced are volts. I and many others know
how to calculate forward and reflected voltages and currents, and their
sums. What's at issue here is where the imaginary waves of average power
are going, what they're bouncing off, and why. Correct me if I'm wrong,
but power is generally expressed in watts, BTUs per hour, or other more
arcane units, but not volts.

Let's try again. The source is providing 40 watts, 32 watts of which is
delivered to the transmission line. The transmission line is
transferring this 32 watts of power to the load. In the transmission
line, we can calculate that there's 50 watts of "forward power", and 18
watts of "reverse power". How much of that 18 watts of reverse power is
going through the source resistor to reach the source to "engage in
destructive interference"? What does it interfere with? How does
whatever it interferes with get there? Does any of the power going
either way, forward or reverse, get dissipated in the source resistor?
If so, how much and why? If not, why not?

In your "explanation", I don't see a single figure in watts, except that
"we have 23 watts of constructive interference occuring toward the
load". (Where is this interference occurring, that is, just where is the
point "toward the load" located? Where did the 23 watt figure come from?
How much of it is "forward power" and how much "reverse power"?) It's
not an explanation at all, but hand-waving.

And why do you insist that every combination of voltage source and
resistor be a "Thevenin equivalent"? I suggest you go back and read your
basic circuits texts, where you'll find that a Thevenin equivalent is a
circuit which is used to substitute for a more complex linear circuit to
simplify analysis. The electrical circuit components used here are not a
substitute for anything. And there's no rule, except something
apparently stuck firmly in your mind(*), which prohibits calculating the
power dissipated in a resistor. No matter what it's connected to. I make
no claim that the power dissipated by the resistor represents anything
but the power dissipated in a resistor, that the resistor represents
anything but a resistor and the voltage source anything but a voltage
source. It is not a Thevenin equivalent, it's a painfully simple
electrical circuit (alas, so simple it's difficult to obfuscate). It
doesn't matter if you can trust a Thevenin equivalent for internal power
calculations. There is no "internal power" here -- it's all out in the
open where we can easily measure and calculate it.

There's nothing in that "black box source" except an ideal voltage
source. You can find a description of this fundamental electrical
circuit component, including its complete terminal characteristics, in
the circuit analysis textbook of your choice. People skilled in the art
are able to calculate the power it produces by multiplying v across it
times i flowing from it, and the average power by applying the
mathematical definition of average to the calculated power. In this
case, it produces an average of 40 watts (100 volts times 0.4 amp).

So please tell us how many watts are going where, what they do when they
get there, and why. If you can't, you don't have a theory at all.

(*)Forgive me, I just can't shake the image of a certain memorable scene
from the movie "The Long Kiss Goodbye" as I write this.

Roy Lewallen, W7EL

Cecil Moore wrote:
Roy Lewallen wrote:

Where's the "reverse power" going?


Since we can calculate 23 watts of constructive interference
occuring toward the load, using the conservation of energy
principle as explained by Hecht in "Optics", we can deduce
that the reflected power is engaged in destructive interference
inside the black box source. Using Dr. Best's conventions:
V1 = 32v, V2 = 18v, Vfor = 50v, Vref = 30v

Any theory that doesn't work in a circuit composed of simple elemental
electrical circuit elements is suspect to say the least. Are you
saying yours doesn't?


It works just fine. Pfor = P1 + P2 + constructive interference.
But that still looks like a Thevenin equivalent to me, you know,
the one we cannot trust for internal power calculations.