[time-nuts] TAPR TICC boxed
holrum at hotmail.com
Sun Apr 2 23:55:39 EDT 2017
I could use the 1PPS output of a crappy GPS receiver. Should have at least 30 ns of jitter. Or for finer, but still noisy, the PPS from the Venus timing receiver is around 6 ns. I'd need at least 100 feet of PTFE coax to get it out the door and back inside with enough cable outside to make a difference. Alas, I have none.
Or I could do it all indoors and set the air conditioning to around 20C and let that cycle the temperature. Or put the cable in the freezer and monitor it while it warms up... hmmm... that sounds fun and easy to do.
I've been pretty amazed by what a TICC can do for $200... I wonder how a GPX chip based one would perform?
I used the TICC to dial in my HP-5065 freq to around 1E-12. I had not adjusted it for a couple of years and it was around 1-E11 off.
From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Sent: Monday, April 3, 2017 3:05 AM
To: Mark Sims; Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] TAPR TICC boxed
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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