Copper jacketed low density PTFE insulated coax cables typically exhibit a net phase change of over 1000ppm during the PTFE phase transition. See figure 2 p14 of the Cables and connectors supplement to March 2017 microwave journal. Solid PTFE insulated cables exhibit an even greater (2 -3x) phase change. to achieve a phase shift tempco of 10ppm/C either hermetically selaed silicon dioxide powder insulated coax or "phase tracking" semirigid or better phase tracking flexible coax is required.
Bruce > > On 03 April 2017 at 21:22 Attila Kinali <att...@kinali.ch> wrote: > > On Mon, 3 Apr 2017 15:05:55 +1200 (NZST) > Bruce Griffiths <bruce.griffi...@xtra.co.nz> wrote: > > > > > > For even more fun you could try to detect the PTFE phase change at > > around 20C using a cable with PTFE dielectric. > > > > > > This will require several 100 meters of cable to be measureable with > the TICC. Modern cables are all <500ppm/K, good cables <10ppm/K, phase > stable cables reach even <1ppm/K. Measuring a change of 10ppm with > a resolution of 60ps means that the delay has to be in the order of 6µs, > which is close to 1000m of cable. Even if dithering gives another facor > of 10, this still means 100m of cable. > > For this level of comparison I would suggest to use a sinusoidal signal, > instead of a pulse, and do phase comparison, which gives a resolution > in the order of 1ps with very little effort, thus reducing the required > cable length to 10-20 meters. > > Attila Kinali > > [1] "Temperature Stability of Coaxial Cables", Czuba and Sikora, 2011 > http://przyrbwn.icm.edu.pl/APP/PDF/119/a119z4p17.pdf > > -- > It is upon moral qualities that a society is ultimately founded. All > the prosperity and technological sophistication in the world is of no > use without that foundation. > -- Miss Matheson, The Diamond Age, Neil Stephenson > > _______________________________________________ > 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.