[time-nuts] ADC sample voting algorithm?

[Nick Sayer]

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)?