[time-nuts] Re: My new GPSDO - U-Blox M8

[Geoffrey Baehr]

Hi folks. Some hopefully helpful thoughts on using a U-Blox M8, politely. (This is for a timing setup).

1. If you go for a Ublox M8 Huawei board, as, I did with a Pi5,  here is an excellent  and I mean
*excllent* tutorial on adjusting  the M8 settings (and the Pi).

https://github.com/tiagofreire-pt/rpi_uputronics_stratum1_chrony/blob/main/steps/advanced_ublox_m8_tuning.md

I could not figure out why my chronyd with PPS  was
outside of lock until I carefully followed those instructions. Forget the 400+
page manual, you will drive yourself crazy, some settings interact with
others, some dont.  Some are completely obscure.

2. My problem was that it defaulted to GNSS time, you want UTC output. etc etc. Use the U-Center
program, I run it under Parallels with a DSD Tech Serial-USB,  SH-09C dongle

3. All credit goes to tiagofreire ! His work saved me HOURS of fiddling. Kudos !

4. Also read his “Advanced System Tuning”, he turns the Pi in to a mini kinda TCXO too. Slick.

5. The reason for a pi5, not a 4, is that the UART is hanging off of  USB in the 4, where now it’s
integrated in to the Bcom all in one, ie direct bus attach. Dramatic jitter reduction in messages.

 6. If you want to get really fancy, you can go for PTP and Ethernet frame coalescing on the Pi.
Apple guys, dont go to the trouble of PTP, as their enet drivers  (and HW) dont support it :-(
I found this out after I went to the trouble of enabling PTP on the Pi, naturally.

7. I got the entire M8 board for $27 on Ebay, not bad.

Side bar note -  As to master freq, my lab std is a GPSDO using a Symmetricom timing board and  TCXO
which outputs 10 MHz. It’s good enough to not introduce noise in to the timebases of
the various instruments. Using an HP 5334B counter, it’s dead on the money. $209.00 Ebay.



[GPSDO Symmetricom Inside GPS 10MHz 1PPS GPS Disciplined Clock&GPS Ant Display  - Picture 1 of 4]

Hope all this helps someone.

Rgds to all


geoff