As a practical matter, in the lab we seldom need a cable delay measured to better than +/- 0.5 ns, which we usually do as a time interval measurement, with a 1 pps into a tee on channel A of a TIC and then the cable from the tee to channel B.
For cables up to 40 m or so, just measuring the physical length is as accurate (experimentally determined!). A while back, EURAMET ran a pilot where a few lengths of cable were circulated amongst a number of NMIs who then had to measure the delays. The reported scatter was about +/- 1 ns, as I recall. This mainly came down to differences in test signals, trigger levels etc. Cheers Michael On Fri, Jul 1, 2016 at 7:03 AM, Dr. David Kirkby (Kirkby Microwave Ltd) <drkir...@kirkbymicrowave.co.uk> wrote: > On 30 June 2016 at 09:19, Scott McGrath <scmcgr...@gmail.com> wrote: > >> If the nominal velocity of propagation is known and length is known delay >> is easily determined mathematically >> > > Except that coax does not have a uniform impedance or velocity factor. Both > will vary as a function of position and frequency. How relevant this is > depends on the accuracy you require, but since it is time-nuts, it is > reasonable to assume that such a simplistic method is not of the standard > expected on time-nuts. > > Dave > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.