Hi
> On Oct 29, 2018, at 3:42 PM, Attila Kinali <att...@kinali.ch> wrote: > > On Mon, 29 Oct 2018 12:03:25 -0700 > Hal Murray <hmur...@megapathdsl.net> wrote: > >> If I go looking for good cables, do they specify temperature coefficient? I >> don't remember ever seeing it when scanning specs, but I probably wasn't >> looking for it so I could have skimmed over something. > > Yes. The key word here is "phase stable coax." If you search for that, > several cables will pop up. They wont be cheap, though. > > >> What determines the dispersion of a cable? Is it as simple as bigger wire >> (more copper) is better? > > For us, it's mostly the frequency dependence of the dielectric. > If you go for higher frequencies, it also becomes a matter of > the different modes a cable supports, which all have different > velocities. The latter is the reason, why GHz cables and connectors > are becomming thinner and thinner as we go up in frequency. > > >> Why do I care about the dispersion as long as all cables match? > > Because it degrades the slew rate of the pulse. If you have > a very bad case of dispersion (combined with long cables), > the rising slope will look more like a jagged mountain range > than a step (though it's unlikely you hit that with modern > cables, unless you go for several km of cable). Attached is > a picture of what it might look like. > > If you remember the old telegraph and telephone lines, they > all used to have inductors placed on them every few km, to > compensate the dispersion. As most of our communication these > days is digital and we have relative short lengths before a > regeneration step happens, there isn't much need for dispersion > compensation anymore. Unless you go for submarine cables or > optical fibers, both of which have elements with negative > dispersion inserted. Even worse things can happen when you have an air dielectric cable and evenly spaced supports. Putting a pulse into something like that can be *very* messy. Bob > > Attila Kinali > > -- > <JaberWorky> The bad part of Zurich is where the degenerates > throw DARK chocolate at you. > <dispersion.png>_______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.