Is it easy enough for you to check the value of register 2 in your ProgRocks when they're on frequency, and then again when they're off frequency by whatever error you're seeing?Robin,
I've never been too bothered about register 2, it's either set for accuracy if there is no GPS or it sets itself. When setting manually I've not noticed any non-linearity.
The attached picture taken some time ago shows my Progrock set at 14.996MHz from a cold start. As it starts about 2KHz off I guess register 2 was about 4KHz away from correct.
As you see it rapidly corrects and settles 2Hz lower than the GPS derived marker (Neo 7) at 14.996MHz. (Bottom spectrum, RX not quite accurate) Looks like register 3 is 0?
If I set register 2 I can make it more accurate but if the GPS is connected it will settle 2Hz low and stay there. I have done more extended tests to confirm that within a few tenths of Hz.
A restart will then be close to the wanted frequency.
I suspect this test was with a 26MHz TCXO which might explain why the frequency settles 2Hz low. All my available synth boards are now non-standard, I cannot repeat this with a standard crystal but it does show how the control works and that it settles as near as I can see at a constant frequency.
I'm not sure what GPS I used, possibly a Neo-7, maybe an old Garmin. I've not got a QLG1.
I can set reg. 2 to a proper value to give the correct output frequency, set reg. 3 to something very high (30),Why 30? I would think 5 was as much as anybody would want, zero if you are looking for real precision.
I wish I could help further.
73 Alan G4ZFQ