>"The tuned circuit, consisting of a coil and a capacitor connected together, acts as a resonator, similar to a tuning fork. [64] Electric charge, induced in

>"The tuned circuit, consisting of a coil and a capacitor connected together, acts as a resonator, similar to a tuning fork. [64] Electric charge, induced in the antenna by the radio waves, flows rapidly back and forth between the plates of the capacitor through the coil. The circuit has a high impedance at the desired radio signal's frequency, but a low impedance at all other frequencies.[65]" [...] >"The earliest crystal receivers did not have a tuned circuit at all, and just consisted of a crystal detector connected between the antenna and ground, with an earphone across it. [1][69] Since this circuit lacked any frequency-selective elements besides the broad resonance of the antenna, it had little ability to reject unwanted stations, so all stations within a wide band of frequencies were heard in the earphone[51] (in practice the most powerful usually drowns out the others). It was used in the earliest days of radio, when only one or two stations were within a crystal set's limited range." [...] An important principle used in crystal radio design to transfer maximum power to the earphone is impedance matching .[51][71] The maximum power is transferred from one part of a circuit to another when the impedance of one circuit is the complex conjugate of that of the other ; this implies that the two circuits should have equal resistance .[1][72][73] Opinion: There's a lot of great concepts here in this -- the most simplest of radios!