One of the earliest memories of radio and music I remember was from when I built my first crystal radio set. It had those spring things you used to connect the wires. It came with everything needed including an ear plug. Unfortunately I could only pull in one station, and it signed off at around 6pm. Sheesh! Remember when stations would actually sign off? Now I feel old:(
The thing that blew my mind was there were no batteries! Damn! Radio waves were just flying around waiting to be captured!
Anyone else have a crystal set that they remember? I may have to try building those "trench radios" from WW1 just for fun:)
md

If they don't have energy, how do they work?

These crystal sets are used to pick up only AM? are they available for FM too?

Here in Chile, some stations until very recently signed off at around midnight - a holdover from having a military government.

Chris

chris,
good freaking question! I don't know how they were powered:(
Perhaps Rob or some other crystal radio fan can explain? If anything I believe it had something to do with the diode that recieved the signal. I hope someone can either correct me or explain:) I am here to learn too!
md

Crystal radios have no power supply or batteries. They used the electricity present in the radio wave itself to provide the power. Thats why you need a good sized antenna with a crystal radio to capture as much of the radio waves as possible.

Mike

Oh yes, I remember crystal radios. I had a philco crystal detector, but I too could only get one station as I lived only a mile from a heavy weight 24/7 AM (KCBS) station that swamped out all other stations.

There are still active crystal groups that publish plans and other stuff. I'm sure a goggle search would turn some up.

Theory? Well lets see. There is usually a tuned L/C input circuit to try and select a given frequency, then the RF signal is rectified to pulsating DC by the crystal (usually germanium). The crystal is nothing more then a primitive diode. Then a small bypass capacitor shunts the RF component to ground but lets the amplitude modulation (audio frequency) pass onto the headphone. As there is no power, there is no amplification avalible so sensitive high impedence headphone were required to help with the otherwise very weak signals. A long wire outdoor antenna is needed so as to try and get as strong an input signal as possible. 100 ft. signal wire routed as high as possible is the usual recipe.

FM? no, only audio amplitude (AM) modulation can be demodulated with this simple rectification method.

I think a simple crystal kit would be a great way to get a child or grandchild interested in electronics if given at the right age, say around 10 or so.

Lefty

thanks mike and lefty!
that's what I was, a simple kid who wanted to get into radio:)
No batteries, and you can hear music!
Just so you guys know, I also got a toot a loop( panasonic) and an early toshiba transistor radio...I was really getting into this :D
md