[time-nuts] High-end GPSDO's

Bob kb8tq kb8tq at n1k.org
Thu Aug 16 17:14:55 EDT 2018


Getting into the ~2 ns region is not as hard as it once was. The real gotcha is needing 
a L1/L2 receiver to do it *consistently*. If you just have L1, then you can easily get more
than a couple of ns over a day due to various atmospheric effects. 

It’s not at all clear what sort of GPS they have in these boxes. (at least not with a quick Google
check). If it’s an L1 / L2 device they could probably hit 2 ns on a consistent basis. If it’s L1 only
it would depend a lot on conditions . Simply put - I’d look closely at the data sheet to see just what
is in the box. I’d ask a few questions about the conditions the testing was done under. 


> On Aug 16, 2018, at 2:40 PM, Ralph Devoe <rgdevoe at gmail.com> wrote:
>     I've seen several spec sheets on high end GPSDO's that seem to have
> performance approaching a low-noise cesium standard, but only cost $3-6$K
> new. One is the SRS FS740 which appears to combine a GPSDO with the
> interpolator of the SR620 counter. This gets down below 10(-13) in one day
> and drops below 10(-14) for longer times.  The other is the EndRun
> Technology  Meridian II, which has been tested at NIST, as shown in
> https://www.endruntechnologies.com/pdf/NISTReport-EndRun-MeridianII-US-Rb.pdf
> .  This shows a TDEV <2 ns (according to NIST) and and ADEV that gets into
> the 10(-15)'s for times longer than 1 day.
>      Has anyone had any experience with these?
> Ralph DeVoe
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