I subscribe to the very interesting QRP-L mailing list, and recently read an article by Michael Rainey, AA1TJ about an interesting radio and set of QSOs that he conducted. Michael’s experiments are amazing and cool, but I think his latest effort takes the cake: he had a number of QSOs using a transmitter powered entirely by the power of his own voice. He calls the project El Silbo and it is a transceiver which uses a loudspeaker as a generator that drives a very low power transmitter. I find it interesting because it is obvious that if you tried to yell, you might be heard over a distance of one or two kilometers, but Michael was able to use the same power to communicate over distances greater than a hundred kilometers. Very cool.