[time-nuts] ADC sample voting algorithm?

[Bob Stewart]

Hi Nick,
Are you applying sawtooth correction to your phase measurement?  If not, are you merely seeing a hanging bridge that dissolves into at a normal sort of tick-tock movement?
Bob

      From: Nick Sayer via time-nuts <time-nuts at febo.com>
 To: Discussion of precise time and frequency measurement <time-nuts at febo.com> 
 Sent: Wednesday, October 5, 2016 6:45 PM
 Subject: [time-nuts] ADC sample voting algorithm?
   
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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