Following-up on earlier analysis, the ADC performance observed at small decimation (like 1 s averages, with 60 Hz data rate – 60x decimation) left something to be desired – quite a few bits lost due to mains (and/or other) sinusoidal noise.
Obiously, there are some bursts. And these are almost certainly not related to the ADC or anything internal to the circuit. Maybe the power supply, but added quite a few decoupling capacitors…
So, if the noise source is external, a bit of shielding might help – great to have a little metal box (even a steel box) at hand!
Note the 2 BNC cables – rather than one – feeding the test signals from a fully-differential source, to avoid ground loops.
Well, not much to add! Amazing what a little metal box can do!