[time-nuts] GPSDO vs Rb standard

[Bob Camp]

Hi

One cycle of 10 MHz would be 100 ns. 100 ns per second would be 100 ppb. 100ns per 20 seconds would indeed be 5 ppb.

Since the Rb is *stable* but not *accurate*, the real question is - how much does the 5 ppb change by? The Rb can't tell you if the GPSDO is correct. The best it can do is tell you if it changed. If you can demonstrate that the GPSDO is locked up, and that it's stable for many days, you can reasonably conclude that the GPSDO is accurate. 

I'd say the first step is to get the Rb tuned closer to the GPSDO. You should be looking for < 0.01 ppb changes. That's going to be tough with a 5 ppb offset. 

Bob
 
On Sep 18, 2013, at 5:47 PM, Bob Stewart <bob at evoria.net> wrote:

> I hooked the Rb's 1PPS to the trigger input on my old Tek 455, 10MHz 
> GPSDO to Channel A, .05us trace, and turned the lights out so I could 
> see it.  The 10MHz is marching right to left about 1 cycle every 20 
> seconds.  So, can I say that the Rb considers my GPSDO to be too fast by about 5ppb?
> 
> 
> Bob
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