[time-nuts] GPSDO Alternatives

Charles P. Steinmetz charles_steinmetz at lavabit.com
Thu Dec 6 21:35:48 UTC 2012

Don wrote:

>you guys are reinforcing that just because its' cheap won't mean it 
>won't work.

Of course it doesn't.  But keep in mind that "working" spans several 
orders of magnitude in this area, and what one needs to design and 
build depends on what degree of "working" one needs to support the 
uses to which the finished standard will be put.  First, there is 
performance during normal operation (good, continuous satellite 
tracking) -- ADEV at all taus of interest, PN at all offsets of 
interest, distortion and spurs, residual AM, stability over 
temperature, PPS jitter, etc.  Then, there is performance with poor 
satellite visibility, and finally performance in holdover (no 
satellite visibility) for however long one needs it (if one needs it 
at all, which many amateurs may not).  For some, there will be power 
consumption issues.  There may also be issues of interfacing to 
monitoring devices, both simple (e.g., LCD status displays) and 
sophisticated (e.g., computer running Lady Heather or Z38xx).  Does 
it need to work with existing programs, or is writing a new 
monitoring program part of the project?  Then there are the 
construction issues.  Does it need to be assembled entirely from 
connectorized modules, no soldering required?  Or capable of being 
thrown together on a scrap of perfboard?  Or will a PC card be 
designed?  If so, can it use SMT parts?  How adaptable must it be, 
particularly in accommodating different oscillators?  Does it need to 
support rubidium oscillators as well as quartz?  Etc., etc., etc.

Thunderbolt and Z38xx commercial GPSDOs are plentiful and relatively 
affordable, so they are natural benchmarks for any DIY project.

 From my perspective, the most interesting development would be an 
offer by someone with a very well equipped lab to test any DIY GPSDO 
with a consistent protocol and publish the results.  That way, we 
could all see how the various approaches compare with respect to the 
characteristics that are most important to each of us.

Best regards,


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