Detection:

The diode can recover the audio signal from radio-frequency (rf) ac. This is known as demodulation or detection. When diode detection is to be efficient, the diode must have low junction capacitance. Then it works as a rectifier at rf, passing current in one direction though not in the other.

Some of the rf diodes are microscopic versions of the old cat whisker, in which a fine wire was located in contact with a crystal of a mineral known as galena. The Components of this type are termed as point-contact diodes and are designed to reduce the junction capacitance. In this manner, as the frequency becomes higher and higher (up to a definite maximum), the diodes keep acting such as rectifiers instead of starting to behave like capacitors. This makes point-contact diodes good for use at rf.