[time-nuts] TAPR TICC boxed
bruce.griffiths at xtra.co.nz
Sun Apr 2 03:22:02 EDT 2017
Its usually not possible to uniquely assign individual channel delays in this way, however swapping cables allows the cable delay mismatch to be eliminated from the measurement of the differential delay between channels.
Eliminating the effect of cable delay mismatch can be useful when adjusting narrowband quadrature splitters ect.
> On 02 April 2017 at 13:38 Mark Sims <holrum at hotmail.com> wrote:
> The new TICC support in Lady Heather has an "autotune" function that can null out the cable and channel delays. You connect a signal (like 1PPS) to both channels through matched cables (like via a T adapter) and it averages the difference and sets the "FUDGE" factor for one of the channels to null out the net offset. It doesn't null each channel individually. You might be able to swap the cables and work out how to allocate the offset to each channel. My unit has a channel offset of -305 ps (part of which could be due to mismatches in the "T" cables / connectors).
> Autotune also calculates the FIXED TIME2 values if you want to play with that feature which can allegedly reduce the device noise by sqrt(2). I'm not sure how well that works since the TIME2 values do drift over time and I don't know how much of an error in the TIME2 settings affects the device enough to make it perform worse than with the default automatic TIME2 mode.
> > The whole delay difference thing does get into a “do you care?” sort of category. The
> testing process you are doing may well calibrate out (or ignore) an offset of this nature.
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