Full details of how a crystal radio works, right down to the electron level.
We start with a demonstration of all the parts in action, showing how the radio waves interact with the antenna and antenna coil to produce a fluctuating magnetic field, which induces electron flow in the tuning coil, which works with the tuning capacitor, which is followed by the diode and crystal earpiece. We talk about why a leaky germanium diode is needed with this particular circuit or how a bypass resistor can be used instead.
That's followed by how the tuning is done using a tuning coil in parallel with a tuning capacitor, which together are tuned to a resonant frequency the same as the radio frequency by adjusting the coil's inductance and the capacitor's capacitance.
Then we show how a radio wave is formed from a microphone's audio wave using amplitude modulation (AM). This then shows how the diode is necessary for converting the radio wave back to an audio wave for use by the earpiece or speaker.
Next we discuss selectivity versus sensitivity and why a separate antenna coil is used.
An finally we show a few other crystal radio circuits.
Thanks to the following for reviewing development versions of this video:
Slovenija12345 of http://www.youtube.com/user/Slovenija...
Charles Wenzel of http://www.techlib.com/electronics/cr...