This repo is where I do all of my ENF work. I collaborate with Bellingcat's open-source team to work on parts of the ENF matching process. I've started collecting European ENF data; read the writeup on my blog.
I found a website that displayed ENF data of the European grid: https://mainsfrequency.com
This was good, so I tracked where it was sending its requests:
https://netzfrequenzmessung.de:9081/frequenz02c.xml?c={number}
Where {number} was randomly generated between 0 and 310,000. Then, I started trying edge-case numbers (0, 310000, 310001, -1, -31). -31 and 310000 always seemed to work, whereas other ones were sketchy or didn't work at all. So, I started a script (running on HackClub's Nest, which is amazing (and free!!)!!) that would write the data from this server every second. I write every day of data to a CSV file, but then I also chunked my data by day, limiting each file to 86.5 thousand lines. Every month, I run a script that compiles each day into one massive month-long Parquet file (which is better than CSV at that size), which you'll soon find published here.