Bruce Griffiths wrote: > Hal Murray wrote: > >> If so, what's the mechanism? >> >> I know that attenuation is frequency dependent due to skin effect but I >> can't >> turn that into variable delays. Is there a magic term I should google for >> and/or does anybody have a good URL? >> >> Context is a memory from 20 years ago. I think it was a data sheet or app >> note for clock recovery on a T1 line. Maybe it was just explaining the >> specs >> for a line amplifier. The idea was that the recovered clock would shift >> depending on the frequency of the signal. The frequency depended on the >> data >> pattern so you could harass the clock recovery by picking nasty data >> patterns. >> >> I think I almost understood it back then when I had the info in front of me. >> >> I've tried to remember or reconstruct it a couple of times over the years, >> but I've never been successful. >> >> >> >> > Even in the RF region where cables act like distributed LC transmission > lines with a relatively constant characteristic impedance, all > dielectrics are lossy. > A lossy dielectric has a frequency dependent dielectric constant. > This is particularly evident in the vicinity of an absorption edge. > Even remote from an absorption edge the dielectric constant varies with > frequency. > The dielectric constant behaviour as a function of frequency can be > approximated by a Cole-Coles relationship. > This in turn can be approximated by a set of Sellemeier equations, one > per absorption edge. > Dielectric loss (and dispersion) increase with the water content of the > dielectric. > > At lower frequencies the cable acts like a distributed RC transmission > line with a strongly frequency dependent characteristic impedance and > propagation delay. > Google telegraphers equations for details. > > > Bruce > > For measurements of the dispersion (variation of propagation delay with frequency) of coaxial cable in the RF region see: http://www.ece.vt.edu/swe/lwa/memo/lwa0136.pdf
Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
