Rick,
On 12/01/2014 07:11 PM, Richard (Rick) Karlquist wrote:
On 11/30/2014 11:09 PM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
I think I have a flaw in my understanding of this.
How can something like an SR620 measure the ADEV of an oscillator, if
the
oscillator is of a similar or better than the reference fed into the
SR620?
What HP did with the 10811 was to make a few special crystals that
were 500 Hz off frequency and build them into oscillators. These
oscillators were mixed with the DUT and the 500 Hz beat note was then
squared up and its ADEV measured with a frequency counter. After
measuring a bunch of production line oscillators, they could establish
a minimum ADEV that would be attributed to the offset oscillator. If
this level of performance wasn't good enough, other offset crystals
could be tried until a "golden" crystal was found.
I remember that HP had some simpler mixer-squarer box that could be
used. Essentially the same as the NBS receiver chain.
> I was thinking it might be possible if one has 3 oscillators and 3 time
interval counters to perhaps solve 3 simultaneous equations. I can't
prove
that, but it seems intuitively correct.
In theory this makes sense, however, it would require a high offset
crystal and a low offset crystal to do a 3 way round robin. There
wasn't enough need to go to the trouble of having 2 crystal designs.
There is an NBS paper written maybe 40 years ago explaining the magic
of the beat note method.
Thinking of the NBS phase-noise set or Dave Allans DTMF paper?
Cheers,
Magnus
_______________________________________________
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.
