[time-nuts] Methods for comparing oscillators

John Miles jmiles at pop.net
Mon Aug 3 04:59:22 UTC 2009


The spec for the 10811A's trimmer range is +/- 10 Hz, actually.  Seems
doable.

There was a good thread on the list back in late 2006 where some of the
pitfalls of the DMTD technique in general were discussed.  It seems that
achieving optimal performance is a lot less trivial than anyone would like.

If someone wanted to build a "minimum effort" system with a lower short-term
floor than the 5370, my understanding is that it would require:

- a 10811-class OXCO tuned to generate beat notes of several Hz
- a mixer of some sort with good IF response down to DC
- four good isolation amps (which thanks to Bruce's recent work is not a
difficult or expensive issue)
- some sort of delay compensation on one of the inputs may be needed to
avoid decorrelation of the transfer oscillator's effect between the two
channels
- a sound card with good differential-phase stability

Of course a 5370 or other two-channel TIC could be used instead of an FFT
back end, but I'd be interested in seeing what level of performance could be
expected with a sound card, too.  Bruce, you were looking at differential
jitter and delay on stereo sound card channels at one point, weren't you?

If differential phase stability is a problem, then perhaps one of the
channel IFs could be heterodyned up to a different carrier frequency that
could share a single physical ADC channel.  Isolation and phase-delay
compensation would again be a big deal in any such scheme.  Probably the
heterodyne LO would need to be derived directly from the transfer
oscillator.

-- john, KE5FX


> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> Behalf Of Tom Van Baak
> Sent: Sunday, August 02, 2009 9:14 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Methods for comparing oscillators
>
>
> >A 1Hz offset may be convenient as its easy to adjust an 10811A or
> > similar to achieve this.
> > A 10Hz offset is harder to achieve.
>
> Would either of these be 10 Hz solutions?
> 1) open the 10811 and change the xtal load capacitance, or
> 2) change the oven temperature set point until the resonator
> is 10 Hz off. You'd loose a little in tempco but...
>
> /tvb
>
>




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