Crystal radio

Principle

A crystal radio receiver is supposed to opperate without any external energy source but the radio waves, therefore it needs a very long aerial (20m) and produces a very weak sound in earphones. I modified this set to be able to use a shorter aerial and to work on speaker. The big switch on the left, in high position, sets the original working condition, without external energy source.

Connectors for external power and switch to activate audio amplifier and speaker

Global view of the wiring

Antenna amplifier

Antenna amplifier

The antenna amplifier increases the level of the antenna signal to make it higher than the threshold of the diode (or galena) which is approximately 0.2-0.3V. This allows the use of a shorter antenna (a few meters).

Without amplifier, the signal level is only about 200mV

Antenna signal without amplification

Galena holder and cat's whisker detector

On this radio, the galena holder and cat's whisker detector where lacking. I re-made them using mainly aluminium pieces. The tip is a piece of needle soldered on a spring shaped copper wire.

Cat's whisker detector and galena holder

Internal amplifier

In order to produce a audible sound, I integrated an audio amplifier and a speaker in the set, the sound comes out holes drilled under the main coil. The amplifier initially supposed to work on battery with mp3 player was scavenged in an electronics recycle bin.

Audio amplifier integrated in the set

Pictures