I need to assemble an accurately length-matched set of short coax cables. My target is to get a set of 1ns-long cables matched to 10ps or better.
I measured the cables using an HP8753D network analyzer to plot the phase of the S11 parameter of each cable in turn, the far end remaining open. I've adjusted the electrical length compensation to make the phase vs. frequency slope nominally zero. (Linear frequency scale, of course.) That gives me a family of plots like these:
LTspice's plot functions aren't as swoopy as the simulator itself, by a lot. Save the data to a file and use gnuplot.
Cheers
Phil Hobbs
yes reflections and re-reflections combine constructivly and destructivly as the frequency changes
if the period of the "undulations" corresponds to the electrical length of your cables, then that is the smoking gun.
Mark
Open ended 1/4 and 1/2 wavelength stubs can be problematic to measure due to the uncontrolled radiation from the open end. Can you measure the resonant frequency of 1/4 or 1/2 wavelength _shorted_ stubs ?
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