[kurthr]

They are quite simple, but there isn't much AM transmission any more so you wouldn't have much to receive unless you also build a transmitter.

http://www.electroniccircuitsdesign.com/radio-circuits/short...

This one works with shortwave.

https://anarchy.translocal.jp/radio/micro/howtosimplestTX.ht...

This is a simple transmitter.