The modulated signal carrying the information, once radiated by the antenna, travels in space. Since there are so many transmitting stations, thousands of signals reach the antenna.
In demodulation process, the radio frequency carrier is eliminated and the modulation signal is separated (filter).
The modulated wave received by the antenna is fed into a resonant circuit. The diode conducts only when the modulated signal is in positive half cycle. Due to this, the output emf changes rapidly to peak value via forward resistance of the diode. The low pass filter (made of CZ and R) removes the carrier frequency. Capacitor CZ discharges slowly. Another capacitor is used to remove the dc component in the detected signal.