Radio waves and visible light are the same phenomenon, separated only by scale. Green light oscillates at roughly 550 terahertz. The FM station down the road runs at 100 megahertz, a wave three metres long. Your retina has no receptor for it. A USB stick the size of a lighter does. The NESDR SMArt is an RTL-SDR, a repurposed European digital television receiver. The signal path is worth following. - The antenna converts a passing electric field into a current, microvolts of it - The R820T2 tuner amplifies that current and mixes it against a local oscillator, sliding a chosen slice of spectrum down to a low intermediate frequency - The RTL2832U samples that slice with an 8-bit converter and outputs in-phase and quadrature streams, the I/Q pair that encodes amplitude and phase together - USB carries raw samples to the host, and every decision after that point is software The specification is honest about its limits. Coverage runs 100 kilohertz to 1.75 gigahertz, with everything below ...