[time-nuts] GPSDO Alternatives
Charles P. Steinmetz
charles_steinmetz at lavabit.com
Fri Dec 7 22:50:55 UTC 2012
>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.
More information about the time-nuts