Hi At some point the whole get it onto the board / get it off the board thing becomes the main issue. Then it's easier to just make the delay line part of the PC layout.
Bob On Dec 17, 2012, at 8:39 PM, David <[email protected]> wrote: > I wish there was an source for helically wound shielded differential > transmission line like the type used in later analog oscilloscopes. > The only place I know where to find it is oscilloscope part mules. > > Essentially it was transmission line with a ridiculously low velocity > factor. It is great for building instant digital delay lines up to > the low 10s of nanoseconds range in a small space. > > On Mon, 17 Dec 2012 20:04:15 -0500, Bob Camp <[email protected]> wrote: > >> Hi >> >> The nice thing about a spool of coax is that it's got a bit of thermal mass. >> It will average out a lot of minor temperature ups and downs. >> >> Bob >> >> On Dec 17, 2012, at 4:34 PM, Hal Murray <[email protected]> wrote: >> >>> >>> [email protected] said: >>>> If you are trying to set up say a 1 us delay, you will get ~ 50 ps per >>>> degree C in your delay. That's a lot ..... >>> >>> A while ago, [email protected] said: >>>> A long delay cable is fine too. If these are timing receivers you probably >>>> don't need more than 100 ns of delay, once you figure out which receiver is >>>> ahead of the other. The cable tempco is low enough not to worry about. >>> >>> 100 ns is 50-100 feet. That's a reasonable length to work with. But I was >>> curious about the temperature coefficient. Google found this: >>> http://www.hepl.hiroshima-u.ac.jp/phx/notes/cable/cable.html >>> which says: >>> # Belden 8240 (solid) shows a temperature coefficient of around >>> -0.252ps/m/deg in a temperature range between -20 and 30 deg. The >>> coefficient >>> becomes steeper beyond 30 deg. >>> # Belden 8219 (foam) shows a larger temperature coefficient of around >>> -0.352 >>> ps/m/deg than that of 8240 in the similar temperature range. The >>> coefficient >>> becomes steeper beyond 30 deg, but less steeper than that of 8240. >>> # Fujikura RG58-A/U shows the smallest temperature coefficient of around >>> -0.152 ps/m/deg, but in a narrow temperature range between -10 and 20 deg. >>> The coefficient beyond 20 deg is much steeper than the others. >>> >>> To pick round numbers, 30 meters and 3 C and 0.25 ps/m/C gives 25 ps. > > _______________________________________________ > 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. _______________________________________________ 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.
