A while back I posted about a 1973 era field strength meter ( Ham Radio 1.0) that I built and used a very cool NOS Simpson 7458 meter, but put it in a new clear case.
Enter Ham Radio 2.0 – I take the signal from that analog field strength meter and feed it into the ESP8266:
And it transmits the micro voltage readings from the field strength meter over the internet. So – this is about the simplest Analog to Digital “SDR” – hi hi. It is that germanium diode “crystal radio” that you built with a diode and a coil – when you were a kid (more or less). In my case its so broadband (there is no tuned circuit or filter – or even a coil) so it picks up everything!