[time-nuts] ADC sample voting algorithm?

Angus not.again at btinternet.com
Thu Oct 6 03:34:30 EDT 2016


You may have already done this, but if you log the same pulses with a
counter or actual TDC IC you can view it and see how they compare with
your measurements. 
Then you can look at how to get them closer - or find that it's
actually correct and that's just where the pulse is at the time.


On Wed, 5 Oct 2016 16:45:21 -0700, you wrote:

>This is tangentially on topic, I suppose. It’s for my GPSDO.
>I notice periodically that the phase measurements seem “noisy.” You can see that over the course of several seconds the value doesn’t change, then it jumps a bunch and then comes right back.
>My theory at the moment is that sampling the ADC multiple times in a row might help, but then what’s the best way to (quickly) pick which sample to use?
>The mean would allow a bad sample undue influence.
>At the moment, I’ve coded taking 3 samples, averaging them and picking the sample that is closest to the mean. If I’m right, and two of the samples happen to be very close to each other and a third is an outlier, then that seems like it would eliminate it.
>I guess what I want is the mode, but with 3 samples, that’s going to be poorly defined (if at all).
>Anyone have any suggestions (besides a larger sample size)?
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