This crystal or galena radio is one of the many versions available on this website. This is from a documentation from the 70s. The coil is formed by 50 + 50 turns of wire 28 in a ferrite rod.
This circuit, found in a Popular Electronics from 1992, is based on an oscillator and a crystal...
Found in old American documentation, this filter has a 8 dB per octave attenuation. The formulas for...
You can adjust the frequency produced by a ring oscillator with three inverters inserting a...