Craig Buck wrote:
Why doesn't the signal coming back down the line in the reflected portion
cancel out the signal going up the line? And if the up and down part is
out of phase ( as I suspect it would be) why isn't there some kind of
interference resulting in distortion or reduced signal strength?

Signals traveling in opposite directions in a lossless transmission line
do not affect each other except at an impedance discontinuity where
reflections occur. Forward waves and reflected waves are essentially
transparent to each other in a transmission line with a constant
characteristic impedance, and are the two necessary and sufficient
components of the standing wave which is indeed an interference
pattern. Interference can and often does occur without any effect
on the individual EM waves that are involved in the interference.

If the standing waves were visible light instead of RF, one would
see bright spots at the voltage maximums and dark spots at the
voltage minimums. I have learned a lot about transmission lines
from the field of optics.
--
73, Cecil http://www.qsl.net/w5dxp



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