I came across this while looking at all kinds of clocks and the origins of operational amplifiers. I've used these but never realized that you could use the hysteresis to make counters.

I originally found this link:

https://www.pa3fwm.nl/projects/sdr/

About a completely home-grown software defined radio that is on the web as well at http://websdr.ewi.utwente.nl:8901/ , you can use it to listen to all kinds of interesting signals, for instance an atomic clock, DCF77 at 77.5 KHz CW.

That project is absolutely mind-blowingly complex and the fact that it works at all has me amazed.