[time-nuts] GPSDO Alternatives

Charles P. Steinmetz charles_steinmetz at lavabit.com
Fri Dec 7 22:50:55 UTC 2012

John wrote:

>What's *really* interesting, though, is the idea that collectively 
>we might develop some standard measurement protocols that would be 
>reproducible in a number of (amateur) labs.

I agree, but I didn't dare to dream so large when I wrote:

>>  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.

At bottom, any such testing requires (i) a comparison standard at 
least as good (and hopefully at least somewhat better) than the DUT 
at all taus and offsets (which may, in reality, be several standards, 
each doing part of that job), (ii) a reliable TIC (and, potentially 
usefully, frequency counter) that can exploit the stability of the 
comparison standard, and (iii) the capability to process the raw data 
to produce meaningful information.  [Additionally, to characterize 
poor-signal behavior one would presumably use attenuators and a 
well-situated antenna.  Some may not have good antenna sites to begin 
with, and in any case, it would be hard to standardize the signal 
strength between locations.]

My thoughts were (1) for many (most?) of the people who would want to 
build a DIY GPSDO, it would likely be their first "really good" 
standard, and therefore their best; and (2) the range of 
TICs/frequency counters owned by the target base is so wide, and 
covers such a large range of capabilities (to say nothing of whether 
any given counter is in good repair and being used to best 
advantage), that obtaining comparable results from one amateur lab to 
another would be just as much if not more dependent on the individual 
counters involved than on the GPSDOs under test.

However, that is no reason not to push forward with standardized 
measurement protocols, which would focus all of us on what the 
relevant desiderata are and how to measure them.

Best regards,


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