It's possible power a small calculator with a small power extracted from the EM Atmosoherical Noise?
@tomnexus suggests that FM broadcast might be a strong source of continuous radiation - a good place to start. I'd add TV.
So an experiment was done: a broadband RF power meter (up to 400 MHz) was connected to a dipole antenna whose length was set to capture the strongest local FM broadcast station (about 95 MHz). In the very best orientation, -20 dBm was captured from an antenna whose total length is about 1.5 m.
That's only ten microwatts.
At -20 dBm, most any diode  (including germanium and Schottky) is operating in its square-law region, which makes it a very inefficient rectifier, providing DC power far below ten microwatts. Impedance converters might improve harvesting efficiency, but can only approach input power at best.
Most continuous high-power broadcasters locate transmitter sites where real estate is cheap, since large antenna structures require guy-wire supports covering a large area. Sites are often rural, far from urban "harvesters". Only if you find yourself very close to a transmitting site does RF harvesting have a chance.