/diy/ - Do It Yourself

>>1537384
(not my drawing BTW, yanked from the internet)
>The Arduino generation can't into even a basic crystal AM radio!
This is why everyone needs to learn basic analog electronics BEFORE fucking around with microcontrollers.

The coil and variable capacitor form a tuned circuit so you can select a particular frequency (i.e. station).
The diode (detector) turns the tuned RF AC signal into a variable RF DC signal.
The capacitor between the cathode of the detector and ground low-pass filters the RF component of the signal, so all you get is the amplitude variations (i.e. the '''modulation''' of the carrier wave).
Now on the output all you get is the audio signal from the radio station.

If you google 'crystal radio schematic' you'll see some that don't have the filter capacitor on the cathode of the detector. That's because they're counting on the inherent capacitance of the '''earpiece''' (which is a piezoelectric crystal-type earphone or headphone) to filter the RF component of the signal.

>Why do crystal radios need to be 'tuned' to a second station for amplification?
I'm not sure what you mean here. In a crystal AM radio receiver there is no '''amplification''' of anything, it's running entirely on the strength of the carrier wave. That's why you need either a crystal earphone or a high-impedance (~2000 ohm) headphone for it to work at all; there's so little curent available that something like an 8-ohm speaker would give you nothing.

>What prevents them from just using a full-wave rectifier and a capacitor?
A '''full-wave rectifier''' would have double the voltage drop because of twice as many diode junctions, when the signal is so small to start with. That's why you always see these using something like a 1N34A diode, which is germanium instead of silicon, and has a typical drop across the junction of 300mV (or less).