On Jun 11, 12:09*pm, Roy Lewallen wrote:

Can you write an equation giving the supposed dissipation caused
by "reflected power" as a function of transmission line length?

I'll just quote the following from Chapter 24-11 of REFERENCE DATA FOR
RADIO ENGINEERS, 1975 Edition:

QUOTE
A load of 0.4-j2000 ohms is fed through a length of RG-218/U cable at
a frequency of 2.0 MHz. What are the input impedance and efficiency
for a 24-foot length and a 124-foot length?

(Omitting the number crunching shown...)

Tabulating the results,

Input
Length Impedance Efficiency Loss
(feet) (ohms) ( % ) ( dB )

24 0.106-j95 1.1 19.6
124 1.8+j55 0.03 35

The considerably greater loss for 124 feet compared with 24 feet is
because the transmission passes through a current maximum, where the
loss per unit length is much higher than at the current minimum.
END QUOTE

As the input Z for each of these lengths is not the same as their 0.4-
j2000 ohm termination, this shows the dependence of the performance of
such systems on the electrical lengths of the transmission line in
use.

I realize we have strayed into the real world here, because RG-218/U
transmission line is not lossless even when perfectly matched at both
ends.

RF