Samples taken using ATmega8 built-in ADC at 28⅛ Hz sampling rate.  The signal is a 50 Hz noise from the power lines, picked up via a simple wire, with a hand moving closer to and then away from this simplistic antenna.  Please note that the sampling rate is almost four times below the Nyquist rate, making this depiction grossly inaccurate.
Own work
Ivan Shmakov (talk)