On Jun 11, 3:03*pm, Cecil Moore wrote:
On Jun 11, 9:13*am, K1TTT wrote:

NO! NO! NO! *the difference is not due to 'reflected power'... any
difference is due to the impedance change seen by the transmitter at
its terminals.

Please let's be careful to give all the details. The *virtual*
impedance, the ratio of Vtotal/Itotal, seen by the transmitter at its
terminals is:

Z = Vtotal/Itotal = (Vfor + Vref)/(Ifor + Iref)

where all math is phasor (vector) math. Vref and Iref are components
of the reflected wave. So the mismatch is certainly related to the
magnitude and phase of the reflected wave. If the Z0 of the
transmission line is the impedance for which the transmitter was
designed, we can go as far as to say that the reflected wave causes
the mismatch, the virtual impedance that deviates from the Z0 of the
line. Before the reflected wave arrives back at the transmitter, the
transmitter sees the Z0 of the transmission line. The mismatch
develops when the reflected wave arrives.
--
73, Cecil, w5dxp.com

i wouldn't call it a 'virtual' impedance, it is a very real impedance.
it is the steady state impedance seen by the transmitter at its output
terminals. once the transient response rings down the waves in the
line beyond the terminals are irrelevant and the constant impedance
can be used to calculate the voltage, current, and power in the
source. in the steady state (which except in special cases is
entirely adequate for amateur use) the mechanism of generating that
impedance is irrelevant, waves or not it can be represented by a
constant value and the source won't know the difference.