Category: DSP

The crystal set of AM transmitters

audio transformer + crystal oscillator + battery = AM radio

At scitoys.com

http://scitoys.com/scitoys/scitoys/radio/am_transmitter.html

source of radio parts for this type of project:

http://www.scitoyscatalog.com/category/R.html

Radio Shack has audio transformers…

http://www.radioshack.com/product/index.jsp?productId=2103254