I've used various arming rates to the DTS-2070C from 1 Hz to 10 kHz and also varied the averaging block size accordingly such that I will get one reading every second.
That's a very nice plot; textbook perfect. Thanks for posting it.
What GPIB data rate did you actually get for the 10 kHz trace? When JohnM ran the same test on my 2070C it was closer to 0.74 s instead of 1.0 s. I'm wondering if you found a way to get your DTS pacing more accurately.
There is a downside to this approach which should be understood, it will also averaging out the white noise of the DUTs.
Correct. A similar white noise effect can happen if you average the raw data itself. See the plot at the bottom of: http://www.leapsecond.com/pages/adev-avg/
The V-shape of the curves comes from the white-noise limit slope (low taus) and the drift-rate limit (high taus). I have not performed any drift rate compensation and the OSA 8600 has only been heated a few days, so the drift is still a bit high.
Did they flatten out with HDEV? A couple of days warm-up will be enough so that the frequency drift over just 10 minutes can be safely removed in software. JohnM -- is there a linear trend removal option to TimeLab that works on the freq series just like works on the time (phase) series?
A peculiar effect is that to make good readings for low-tau values I need to trim the oscillators to be very near each other. Otherwise there will be a polution of the lower taus compared to my selected good plots. This polution and the slope is insensitive to any drift rate compensation, so Hadamard analysis does not help.
Have you tried better isolation between the two BVA and the DTS to make sure it isn't that? How does the DTS input isolation spec compare to say a TSC 51xxA?
I have not been able to pin-point how this frequency offset effect really works with ADEV, but currently I suspect it has something to do with quantization and averaging... but I haven't had time to verify that.
Yes, this sounds plausible. I suspect the DTS2070 (or HP5370 or SR620) will give better looking (though not necessarily more truthful) results if you hit the very same interpolator bin on every sample. I can send you examples of this. Do you think this might be happening in your case? If so you might be able to make it even more visible if you use one of the BVA as the ext ref to the DTS. Or use the same BVA for both inputs (or all three inputs!). Some cheaper counters avoid this effect with clock dithering. Or you essentially get dithering for free with any lesser grade DUT. But in this experiment you're using two BVA and a DTS so there is almost no noise to begin with. I would think this is very test setup you would use for exposing an interpolator in-a-rut effect if that is what you were trying to do. /tvb _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
