I once ordered a crystal radio from my Johnson and Smith catalog NO POWER SOURCE is what it said just the energy of the radio waves themselves leaping off the sharpened spike atop some clandestine tower spreading out in spherical shells stretched so thin by now there couldn't be and yet there was enough electromagnetic "stuff" to agitate the antenna wire enough to tickle the cats-whisker pin which poked the germanium crystal just so and a highly wound spool of baby's hair wire would tune to a station at night with a guy who made puns and talked about nothing through the plug in my ear which trickle of sound transfixed a boy's head to his pillow all night