Hi They *are* phase coherant to within 360 * 100/ 10 = 36 degrees. You can get them to *maybe* ten degrees with this and that done here or there.
If you want them within a degree, no you can’t do that directly with GPS. If your definition of phase coherent is zero degrees, a pair of SDR’s off the same buffered clock will have issues with that definition in the real world of temperature wandering around ….. Bob > On Mar 6, 2022, at 2:04 PM, Krishna Makhija <[email protected]> wrote: > > Hi Bob, > > I am currently getting +- 10 ns nominal. The antennas are currently almost > next to each other (roughly 1-2 inches apart). Yes, they should be outside > of each of their farfield zones. Here is the PPS offset I am seeing during > measurement: > [image: image.png] > And this is the frequency error I am seeing: > [image: image.png] > Overall, the GPSDOs seem to work pretty well. But the question still > remains if one can hope to get them to be phase coherent, either in > real-time or in post-processing. > > Jeremy: I bought these items by writing to them. I chose to place a > purchase order (since I did it through my organization), but you might be > able to order by talking to them directly and paying using a credit card. > > On Sun, Mar 6, 2022 at 1:51 PM Bob kb8tq <[email protected]> wrote: > >> Hi >> >> How close are you trying to get? >> >> How far apart are the GPSDO’s? >> >> A “run of the mill” number would be out around 100 ns. A “pretty good” >> number is in the 20 ns range. A “crazy good” number would be 2 ns. To >> do better than this, you likely would need to go to a more exotic >> configuration >> on the GPSDO. >> >> Bob >> >>> On Mar 6, 2022, at 12:55 PM, Krishna Makhija <[email protected]> wrote: >>> >>> Hello, >>> >>> I am new to the whole precision time-keeping game (and to this mailing >>> list) so I apologize in advance if my question is too naive or has been >>> answered already in your mailing list. >>> >>> Is it possible to have two separate GPSDOs, each with their own antennas, >>> be phase coherent to each other? I have a Jackson-Labs Fury >>> <https://www.jackson-labs.com/index.php/products/fury> and a Mini-JLT >>> <https://www.jackson-labs.com/index.php/products/fury>. I am using each >> to >>> provide a 10 MHz reference to two separate software-defined radios >> (SDRs). >>> In my tests I find that the phase offset between said SDRs has a slow >>> time-varying behavior. I know the frequency errors of the GPSDOs are of >> the >>> order of parts per trillion which will show up as slow time-varying phase >>> offsets but I was hoping to use the PPS offsets and instantaneous >> frequency >>> errors that I get from these modules (using SCPI commands) to be able to >>> "back out" or predict what that time-varying phase offset would be. Is >> such >>> a thing possible? Currently, the time-varying phase change does not seem >> to >>> follow any discernible pattern and my attempts at backing out the phase >>> change do not match my measurements. >>> >>> Here is the math I am using for calculating what I *think *the phase >>> *should* be: >>> [image: image.png] >>> [image: image.png] >>> >>> [image: image.png] >>> Does any of this seem sensible? Any input is appreciated. >>> >>> TL;DR: Trying to get phase coherence between two separate GPSDOs may not >> be >>> possible but can you use PPS offsets and frequency errors metadata to >>> correct for it in post? >>> >>> Regards, >>> Krishna >>> >> <image.png><image.png><image.png>_______________________________________________ >>> time-nuts mailing list -- [email protected] -- To unsubscribe >> send an email to [email protected] >>> To unsubscribe, go to and follow the instructions there. >> _______________________________________________ >> time-nuts mailing list -- [email protected] -- To unsubscribe send >> an email to [email protected] >> To unsubscribe, go to and follow the instructions there. > <image.png><image.png>_______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send an > email to [email protected] > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
