Back when I collected antique radios, I eventually realized I had absolutely nothing to listen to on AM radio. I decided to build a transmitter so I could broadcast my own AM signal. This originally was built in a wonderful case which integrated the antenna and the tuning LED, but the transmitter broke and I scrapped the case for a PLL temp controller for my temperature controlled water bath. I still have the dead circuit board though, so that’s why it’s on this website. I’m glad I kept it.

Remarks on Circuit

This doesn’t seem like it would work very well, but it does. The oscillator chip creates a square wave at the crystal resonance frequency, which drives the LC tank circuit, acting as a RF transmitter at 1Mhz. Amplitude modulation is obtained by varying the supply voltage of the crystal with an LM386 audio amp, who’s input is the desired audio. We can crudely measure current draw using the LED, which we can use to tune the LC resonance circuit to the oscillator frequency, looking for highest current consumption.

Of course, over modulation of the oscillator will lead to overvolting and destruction. I believe this is why my oscillator developed a hole and loss of electronic smoke, thus bringing my nice little transmitter to its demise.