A crystal set needs no battery power, the signal is enough to power the audio. I had fun making one with those 20 in 1 electronics toys as a kid. I think that one didn't tune so you heard multiple stations at once.
I don't know the theory, though I did make one as a child.
It was the non-tuning type, and would pull in only the strongest-broadcasting local AM channel.
It's also possible to create a tuner which can pull in a specific station (or more accurately: frequency). These can also operate without a battery, though battery-powered radio is of course more versatile.
I don't know the theory, though I did make one as a child.
It was the non-tuning type, and would pull in only the strongest-broadcasting local AM channel.
It's also possible to create a tuner which can pull in a specific station (or more accurately: frequency). These can also operate without a battery, though battery-powered radio is of course more versatile.