Wednesday, January 11, 2006

You are Broadcasting right Now!

It's radio, in a Low Power tenuous sense; a low low power sense.

You can actually use your computer monitor as an AM short wave radio transmitter. All electronic devices emit eletromagnetic waves. In radio we tend to think of this as noise and a cause of interference. Your PC monitor emits EM waves at very high frequencies. So high in fact they are audible on short wave AM radio. When the image on your screen changes the tone it emits changes as well. The range is small, but it's real.

This all starts with two bright kids at Cambridge Univeristy, the devilishly clever Markus Kuhn and Ross Anderson. Their paper is here:

They begin by explaining that high-tech eavesdroppers [i.e. spies] can reconstruct video screen content from it's radio frequency emanations. minimise the energy of these emissions. Today Sensitive government systems use expensive metallic shielding on individual computers, rooms and sometimes entire buildings to prevent this leekage. It's a reversal of this process that converts it into a short-range communications medium.

On the harmless side, Erik Thiele wrote a program that allows you to convert midi files into a code that your PC can then emit using the same principle. Link below: