Crystal radio
From Elliptic Curve Crypto
Building a simple AM crystal radio is, or ought to be, a basic survival skill.
This circuit [1] shows an antenna tuned with an inductor of 240μH and a variable capacitor of 365 pF.
The resonant frequency for this tuning with the variable capacitor set at 365 pF starts at about
- f = 1 / 2π√(LC) =~ 537.73472 kilohertz
If the variable capacitance is reduced to 36.5 pF, then the resonant frequency will be increased to 1700.46649 kilohertz, the other end of the popular AM broadcast radio band, which is about exactly half a decade wide, spanning a ratio of √10 on the radio spectrum.
- ↑ All About Circuits. Textbook // Semiconductors // Practical Analog Semiconductor Circuits // Radio Circuits. https://www.allaboutcircuits.com/textbook/semiconductors/chpt-9/radio-circuits/
