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When was the last time you heard of a signal in a PC trace degrading and then getting much better?!?!!??!!!! So much better that when previously tested that trace wasn't deemed suspicious?

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Look at load line impedances. The effective output impedance of a transmission line depends on the fraction of wavelengths of waveguide transmit the wave. At any half wavelength, the output and input have equal impedances. If the output were matched to the input but no the line you get the exact effect described.

http://en.wikipedia.org/wiki/Transmission_line#Half_wave_len...

Not a PC, but a good story about a PDP-10 back-in-the-day:

http://www.catb.org/jargon/html/magic-story.html

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