Basic Crystal Set
The crystal set is the simplest form of radio receiver but it is also used as one of the building blocks for more complex receivers. It may be constructed from the following circuit diagram. The output level will be very low which is why high impedance headphones are required -
The suggested layout is not critical but sufficient space should be provided between components so that they are easily accessible.
The tuning capacitor will have a control shaft diameter of either 6mm or 0.25 inches depending on its age.
A control knob mounted on the shaft will make tuning much easier.
The number of turns required on inductor L1 for a given frequency will depend on the maximum value of the tuning capacitor C1 -
The 1n (1000pF) capacitor may be mounted on the headphone terminals and the diode D1 connected directly to one end of L1 and one headphone terminal -
Constructors may wish to experiment with the number of turns on L1 and the aerial coupling in order to get the best results. Instead of aerial taps a coupling winding could be employed. This is all part of the fun of learning by trying.
When used in a more complex receiver The capacitor value is usually fixed and the inductor mounted in a screened assembly with a ferrite or iron dust tuning core.
A simple tuned amplifier may be added to the above circuit to increase both the sensitivity and selectivity.