Impedances and transmission line effects...

[ppppenguin]

Mark's cautionary tales should serve as a warning to us all when we're trying to measure something. From the simple EMF vs PD problems he's described to a systematic 0.05dB (yes, a twentieth of a dB and it really mattered) error between a client's measurement and mine on professional video equipment. Took a lot of work to troubleshoot that one. It's relevant here because it turned out to be a return loss problem on some (very expensive) testgear. Fixed by a 6dB pad. But it meant that my client had been sending out all their video routers with a systematic 0.05dB gain error for some years. Since the published spec was for 0.1dB error max, this was using up a lot of the tolerance.