The original idea was to try and correlate phase jitter to space weather, essentially using the mains power system as a sort of radio telescope. I never did get it working (although I did not have much time to try, either). I was able to see interesting things like generators spinning up to maintain the frequency though.
Will open source the hardware when done. I am not an astronomer, just some random fellow that investigates things at depth for no particular reason.
High precision instrumentation just uses a stable comparator to sync the AC line Zero crossing events, and times the sharp roll-off gap over several cycles to estimate the center transition event. This allows readings to be synced in the low-noise state of the power lines cycles, and time what the readings should be when monitoring the voltage, temperature, and current across the cycles.
Additionally, most >8-digit meters internal power supply will have a tuned filter for the 60Hz/50Hz line. Getting a line filter will often give a digit of precision on older equipment, and clip-on line chokes in bulk also help.
https://www.digikey.com/en/products/detail/eaton-tripp-lite/...
One final tip, anything beyond 12bits precision or 60MHz wide RF bandwidth for SDR will almost certainly have an export restriction. Wideband devices also have RF front end saturation issues, and usually require narrow band-pass filters to see the hydrogen line etc. Best of luck =3