Roy Lewallen wrote:
I admit to being hazy about what you choose to call "forward power" and
"reflected power". So that's probably why I don't understand the meaning
of "the reflected power can be greater than the forward power into a
passive load." Does this mean that both "reflected power" and "forward
power" flow into a load? Then, does the "reflected power" flow back out,
to go back down the transmission line, or does it contribute to the load
dissipation?

Forward power is all the power incident upon the load. Reflected power is
all the power flowing away from the load. If the load is passive, the power
flowing away from the load cannot be greater than the power flowing toward
the load. Chipman says there is no "implication that the power level of the
reflected wave is greater than that of the incident wave". He goes on to say
the apparent increase is just a resonance effect.

In Dr. Best's QEX article he shows how V1 + V2 = Vtot but P1 + P2 usually
doesn't equal Ptot. Chipman's equation 7.34 seems to be of the same ilk.
Dr. Best's interference term, 2*Sqrt(P1*P2)cos(theta), has to be added to
the power equation to make it balance. I suspect that Chipman's term,
2*X0/R0*Im(rho(z)) is simply that necessary interference term.

On page 137, Chipman says: "The question arises as to whether the transmission
line equations predict a reflected wave at the termination having a higher
power level than the wave incident on the termination, in violation of the
principle of conservation of energy". He goes on to say that if |X0/R0|=1
then reflected power cannot be greater than incident power. And |X0/R0|=1
is one of the boundary conditions for the lossy transmission line.
--
73, Cecil http://www.qsl.net/w5dxp



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