[time-nuts] TAPR TICC boxed
bruce.griffiths at xtra.co.nz
Wed Apr 5 02:21:32 EDT 2017
The gold standard is a random pulse source.
Using something like a SPAD as the source of random pulses is popular as the average rate can be easily adjusted by changing the light level. It also avoids using radioactive sources.
> On 03 April 2017 at 15:05 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.
> A pulse source with somewhat more pulse to pulse jitter may be more useful in that averaging will occur over a wider range of fine interpolator codes.
> > On 03 April 2017 at 05:34 Mark Sims <holrum at hotmail.com> wrote:
> > I implemented the channel offset compensation feature specifically to make measuring cable delays more accurate. I wanted to measure my TDR calibration cable and another very precision delay line. I used Heather to null out the channel/connector delays and then replaced one of the "T" cables with the TDR cable.
> > My test setup / TICC was coming up with a -306 ps channel offset error. The test signal was the 1PPS output of a FTS4060 cesium. Connecting / reconnecting one of the test setup cables and re-doing the offset test (I was averaging for 1800 seconds) could produce compensation values that varied from -300 ps to -325 ps. Just de-doing the offset test without messing with the cables produced values around -300 to -310 ps.
> > BNC connectors aren't the best for precision timing. I need to re-run the test with SMA cables / T adapter and the precision HP connector torque wrench and see what that looks like. It would also be fun to lay a coax outdoors and see how the delay changes over a day as it heats/cools.
> > --------------------
> > > >
> > > Some “cables” have very long delay numbers.
> > >
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