Why does a radio need a detector?

A diode is used as a detector. The diode passes current in only one direction, converting the high-frequency alternating current into a series of pulses of the same polarity, but of different amplitudes.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.