This historic circuit extracts audio directly from amplitude-modulated radio waves without requiring an external power source. It uses a long wire antenna to capture RF energy and a point-contact diode, traditionally a piece of galena touched by a fine wire, to demodulate the signal. The resulting audio is faint and can only drive highly sensitive high-impedance earphones.
Heard on the job
I built a simple crystal set with the students to demonstrate basic RF demodulation without a battery.
Also heard as
- crystal radio