Having been a time nut for almost 50 years knot knowing it I like to add my thoughts. Starting in the late 60's I won second place at IEEE student contest for my counter design using 7 segment lamp and Motorola RTL in the 70's I buried a Sulzer using bank coin bags filled with sand to close the hole and application notes at TI using TI LED and IC's, in the 80's bought an Efraton FRK and did my first DO using a Tracor Omega converted to 60 KHz and a Philbrick DAC. I was the u processor using every 6 month using the Tracor to recalculate the time for pulses to the DAC counter. I had then and still do now have problems with computers and processors. When Brooks came out with his GPSDO i bought 10 A&A boards and started dialog with Brooks. Thanks to Corby I joined time nuts and continued work with Richard McCorkle. One of the results is a GPSDO for FE 5680, 5650 and 405 that is readied for release by Cash Olsen. It took extensive testing fine tuning and more testing. During that time I also had the opportunity to communicate with pro's on that subject and came away even for the pro's it is not a walk in the woods. Tom's 2008 comparison mentioned in this thread http://leapsecond.com/pages/gpsdo is very informative it clearly shows the relationship between OCXO and digital loop. Few HP units are as good as his and there is a wide distribution when it comes to 10811's. The tbolt shows clearly the impact of the fact that it changes the frequency to correct the 1 pps. Miller is very impressive and we have done one using u-lox-6 and a MV89 with similar results mainly intended for Ham's. Working on a 100 MHz version for Ham uwave work Summary true GPSDO is complex and long time work, Miller is simple and low cost and maximum bang for your buck. One more comment on u-blox. In my opinion unless you plan on doing saw tooth correction the T version is a waste of money. Also if you plan on using the Miller circuit buy a $ 10 version and use a PIC to program in the higher output frequency a version that stores it in EEROM costs three times as much relying on the battery unless it is always powered up may be a problem once you are out in the field and have no PC to change from the 1pps default Bert Kehren In a message dated 4/6/2016 4:20:14 A.M. Eastern Daylight Time, hmurray@megapathdsl.net writes: albertson.chris@gmail.com said: > I may never get around tooth's as the Rb is very good all by itself to the > limit of my ability to measure it. Wait longer. :) If your Rb doesn't have a PPS, make one. One of tvb's divider chips is probably the simplest approach. You can probably do it with an Arduino if you have one handy and like writing that sort of code. Compare the PPS from the Rb with the one from your GPS. It's probably simplest if your Rb PPS is offset a bit from the GPS PPS. The idea is to make the difference always have the same sign. Feed both PPS pulses to some equipment that can measure the time difference. Collect data. If you have a typical low cost (non GPSDO) GPS device, you should be able to make graphs like the ones that show a hanging bridge. Look at a sawtooth region, not a bridge. Pick the top or the bottom or the middle or whatever you can remember. Call that the offset. Wait an hour collect more data. Has your offset shifted? If not wait longer... You are measuring the average frequency of the Rb. It might be temperature sensitive. Can you see the offset change over a day? (That assumes you turn the heat down at night...) Or maybe you are seeing the GPS night/day shift. -- These are my opinions. I hate spam. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.