"Cecil Moore"
What is happening with 1/2WL of Z0=600 ohm feedline
connected to a 50 ohm load on one end and a 50 ohm
source on the other end is interference. Destructive
interference toward the source causes constructive
interference toward the load and the reflected energy
at the source is re-directed back toward the load.

What we want to avoid in our antenna systems is
constructive interference toward the source.
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Whether the source sees that reflected power or not, that reflected power is
stressing the transmission line -- regardless of the electrical length of
that line at the operating frequency.

IOW, for these unique conditions the source may be unaffected by the
reflected power in the line, but the line itself is still stressed by that
power -- and possibly to the point of failure.

RF