I have twice received signals from FR1GZ this morning using WSPR. WSPR is a digital radio signal (details and free software here) designed to pass minimal information with minimal radio power over great distances. Since FR1GZ is the call sign of a radio amateur on Reunion Island deep in the Indian Ocean, this has definitely worked. He is using about 5W of radio power – less than your average taxi radio – and being received clearly many thousands of km away. This is using the 10m (28MHz) radio band – where signals can travel strongly over great distances by bouncing off the ionosphere: but only if there is enough energy from he sun to energise the layers very high above us.