VK4BXI wrote:...the two GPSDO's are moving in different directions at slow but similar speeds it can't be the oscillator causing that.
Either one or both of the GPSDOs is either broken or a bad design. It's as simple as that.
I have two GPSDOs here, an older BG7TBL unit (Chinese, from eBay), and one from Leo Bodnar. They both keep perfect time and frequency (well, within a few milliHertz
).
My first thought was that someone was messing with the signals ....to lower the accuracy due to the ongoing war or something like that. I know that there is a lot going on with the GPS network that is not discussed.
The intentional diminishment of GPS accuracy, called Selective Availability (SA), was discontinued in May 2000. I was directly involved in a major technical effort to support this decision.
While there are certainly aspects of GPS (and, undoubtedly the other GNSS services) that are spooky, the basic functionality of providing precise and accurate time, frequency, position and velocity are monitored both formally and informally by thousands and thousands of people around the world. University labs, surveyors in the field, pilots, the FAA, the list is endless. If something was "off" everyone would know about it instantly.
I would love to believe that the oscillator is at fault but cannot reconcil what I see.
You are suffering from a classic affliction known as
"Segal's Law" Again, the problem is that one or both of your GPSDOs is/are screwed up. This must be the case, by definition, because the world uses GPS and if GPS had some problem, accidental or intentional, the world would know. If both GPSDOs were perfectly in lockstep, or at least damn close (milliHertz of difference--which is very difficult to measure, BTW), then you would not be suffering so.
If you really want to dive deep, the eevblog.com forum is THE place to go. They have lots of interesting discussions about time and frequency accuracy, like
this one for example.