[time-nuts] TruePosition GPSDO performance

[Mark Sims]

I ran a test of the TruePosition 1PPS signal performance using a TAPR TICC.  The TICC was clocked by a HP-5071A.  The TICC was in time interval mode with the Zyfer 1PPS on channel A and the 5071A 1PPS on channel B.   

The TruePosition had been powered up for a couple of days.   Values below tau around 30 seconds are probably better, but the TICC resolution is the limiting factor.

The blue plot is frequency deviation of the 1PPS (1Hz)  signal scaled to 10 MHz from a nominal.value of 10 MHz.  My TADD2-mini dividers were in use elsewhere, so I could not measure the actual 10 MHz output.

It looks like the TruePosition ADEVs are up to around an  order of magnitude worse than the Zyfer Nanosync (but the TruePosition costs 5X less).  

I have noticed that the TruePosition likes to occasionally go into one of its holdover modes despite tracking lots of sats with good signal levels.  The holdovers tend to last a few minutes.  There were not any holdovers in this run.  They don't seem to greatly affect the outputs.
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