Roy Lewallen wrote:
Foldback has nothing to do with "reflected power". It's simply that a
mismatch results in higher voltage or current at the output which could
damage the output device or circuitry. That's why foldback is used.

If the source is connected to a transmission line, the
mismatch results from a virtual impedance other than the
one for which the transmitter was designed. The virtual
impedance seen by the source is (Vfor+Vref)/(Ifor+Iref)
where Vfor is the forward voltage phasor and Vref is the
reflected voltage phasor. |Vfor|*|Ifor|=Pfor and
|Vref|*|Iref|=Pref If it were not for reflections,
the source would see Z0.

DEVIATIONS AWAY FROM Z0 ARE *CAUSED* BY REFLECTIONS!
Deviations away from the design impedance are what
causes foldback.

There are no waves of average power bouncing back and forth
on a transmission line.

One way for that to be true is for reflected energy waves
to contain zero energy but any rational person knows that
cannot be true. Reflected waves consist of an E-field and
an H-field whose ratio is Z0. ExB is watts. Watts are the
unit of power.

Do you really think that the EM waves bouncing back from
your mirror into your eyeballs while you shave contain
ExB = zero watts?
--
73, Cecil http://www.w5dxp.com