[time-nuts] TAPR TICC boxed
bruce.griffiths at xtra.co.nz
Mon Apr 3 08:13:49 EDT 2017
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.
> On 03 April 2017 at 21:22 Attila Kinali <attila at kinali.ch> wrote:
> On Mon, 3 Apr 2017 15:05:55 +1200 (NZST)
> Bruce Griffiths <bruce.griffiths at 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
>  "Temperature Stability of Coaxial Cables", Czuba and Sikora, 2011
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