[time-nuts] TAPR TICC boxed

[Mark Sims]

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.

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> Some “cables” have very long delay numbers.