Testing the preliminary fixed TA520 by measuring the wander of a cheap GPS module PPS output vs. the True Position GPSDO PPS output - or fine arts japanese technology vs. rock solid HPAK:
TA520 and 53131A - the perfect team for timenuttery
53131A directly reads time between PPS, no wait for the impatient
TA520 plots the same measurement over 10 minutes, you'll have to wait 10 minutes for the result
The plot is showing some phase wrapping, where the vertical jumps from 0ns to positive overrange are visible, the TA520 cannot display "negative" time difference, it wraps around to 0.9999999xxx seconds.
Edit: While posting this, another 10min measurement completed, without the wraparound and some more meaningful statistics: