G3RUH GPSDO lock-in time and Kuhne PLL lock

John ZS6JON asked a question about problems with a Kuhne 23cm G3 transverter not locking with a G3RUH GPSDO.  I had some problems originally with my TR1296H and the RUH, but I moved to a Rb ref and now only use the RUH to verify the frequency of the Rb and backup MV89As.  First, here is an example of the lockup time of the Kuhne, from turn-on, with the Rb 10 Mhz ref, tuned 1kHz LF of the Martlesham beacon

The lockup time of my Kuhne TR1296H is about 20s.  I use a Rubidium reference, so this isn’t a problem.  However, I also have a G3RUH GPSDO, and when it is not locked to the GPS, it hunts back and forth with a period of about 32s, with a range of +-800mHz. If the RUH lost lock, the PLL LD light sometimes went out on the Kuhne.

Here is a stripchart of the delta between the Rb ref and the RUH GPSDO after a warm restart (2 second power-off) – earliest time at the bottom of the chart, one minute per division.

Resetting the RUH GPSDO, it takes around 180s for the PLL to start to lock.  I reset it at 12:22:00, and at 13:24:44 it started to pull in.  This is the fifth harmonic, to the offsets from the nominal 600Hz are obviously multiplied by five.  Once the lock-in starts, it takes around 1200s to get within about 5mHz of 10,000,000.000 Hz.

Using a much finer resolution, the last part of the lock-in shows that the lock is pretty much within 2mHz after 40 minutes.  Watching the phase difference using a two-channel scope shows that after an hour, it takes at least 1800s for one complete cycle slip (measured by watching the interval rate of change with the horizontal and vertical scales heavily expanded).  I also have a 6.5 digit voltmeter watching the phase output from an AD8302 phase detector. (ignore the 599.8091Hz label, that was just where I had the cursor…)