On Fri, 07 Dec 2012 17:50:55 -0500, "Charles P. Steinmetz" <charles_steinm...@lavabit.com> wrote:
>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. For myself: 1. My current lack a comparison standard is the reason I would design and build a GPSDO. At best I might buy a used rubidium oscillator at some point. People talk about good deals on Thunderbolts but I have yet to see one. It seems peak Thunderbolt passed before I was seriously looking. 2. So far my best universal counter is a rebuilt Racal Dana 1992 with a TCXO but it lacks GPIB. It might be easier and cheaper for me to duplicate my GPSDO phase detector and add a counter chain and trigger so it can make and report its own time interval measurements against a secondary asynchronous source but that would hardly be reproducible by a third party. 3. I am less interested in this since I will be at the mercy of whatever timing GPS I use and my current antenna environment. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.