I built a (very) short range AM radio transmitter. It's far from tuned and produces a massive amount of interference on a 40 kHz (1 MHz ± 20 kHz) swath. That's due largely to the fact that I used a 1 MHz crystal as the carrier generator, which produces a 1 MHz square wave, which makes for all sorts of nastiness when used in radios. Not to mention all the ringing on the odd harmonics. I need a 1 MHz sine wave oscillator. It's not a huge problem, though. The transmitter only outputs a few microwatts, at the maximum. In my bedroom, it's out of range at about two metres. In my underground, RF-impenetrable, zombie apocalypse-ready EGN3000 classroom, it'll reach about five before it's just too weak to hear.
Regardless, I can pump audio into it and it outputs a (fairly) clean AM signal that I can pick up on my radio (tuned to, obviously, 1 MHz). The SNR is farily low, so there's a lot of noise on the channel, but a lot of that is just the fact that AM sounds like shit.
Recording. We're getting all WWII up in here.
Here's the pictures.
Close up. It's a major jury-rig, too. I didn't have proper audio transformers for the carrier and audio input, so I went all redneck on that mofo and used a couple of common mode chokes that I had laying around.
Here's the amplifier circuit. I found that my laptop couldn't output a loud enough signal to make for a very clear transmission. I just ran a single channel (left, I think) into an LM386 circuit to amplify the input sound.
This is what the output looks like, on the breadboards.
Let's lift the skirt on this bitch. That massive strip of metal at the bottom is a piece of solder-saturated solder wick. It's supposed to be the antenna.
Here's the output.
...and zoomed out.
To anyone interested, I'll post the schematics.