[time-nuts] Did a member of time-nuts buy this?-

Bob Camp kb8tq at n1k.org
Wed Dec 10 22:37:47 EST 2014


> On Dec 10, 2014, at 8:32 PM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
> Bob,
> On 12/11/2014 02:25 AM, Bob Camp wrote:
>> Hi
>>> On Dec 10, 2014, at 8:02 PM, Mike Monett <timenuts at binsamp.e4ward.com> wrote:
>>> OK, so I figure out how to do this. How do I tell if this is making the
>>> gpsdo more accurate? In other words, how do I get the ADEV without having
>>> an H-Maser?
>> You get a Cs (or other atomic standard) or you compare several different GPSDO’s against each other. The preference would be for groups of three so you can rule out ones that are not doing what they should.
> GPS receivers can have considerable common mode effects, which won't show up in the three-cornered hat setup.

Which is why you want several different GPSDO designs with different “stuff" inside them…. 

> You can work with a rubidium clock and a crystal clock if you don't have a cesium standing by.

The GPS is likely to have issues that are 12 / 24 / 48 hour cycle related. Rb’s and crystals have temperature dependance that likely follows the same sort of pattern. That will indeed limit your ability to check things at 1x10^-14 at 400,000 seconds with a 40,000,000 second run. In most basement design cases, keeping that > 1 year run going is unlikely. Most of the debugging and testing work will get done inside the range of the better auction site GPSDO’s.  Working that part out on the cheap first is the best way to do it. 

It’s also a matter of the other gear on your test bench. There is a balance between design, reference standards, and measurement gear. You inevitably move one forward at a time. When you do, you need to revisit the other two and bring them forward as well. Trying to measure to 1x10^-14 with a “Bob’s of Bulgaria (TM pending)” frequency meter is probably not a real good idea ….. 


>> You also need the measurement gear to resolve frequency down in the 1x10^-13 range. A normal counter will not do that.
> Indeed.
> Cheers,
> Magnus
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

More information about the time-nuts mailing list