Just like it says on that page, it is typical of the data exchange between a cell phone and the cell towers. The first part, made up of bursts, is before the call is fully established. The second part, which is a continuous sound, is the actual call itself where voice data is being exchanged. Interestingly, I have heard similar sounds when I've held quite different phones near audio equipment (Verizon CDMA cell phone and a DECT cordless phone). I think that the audio characteristics depend on three things: the data rate, the packet duration, and (for the discontinuous beginning) the negotiation packet duration and rate. It probably does not depend on the RF carrier frequency because the audio equipment is not a real radio receiver - it is just taking the total sum of the RF voltage received, rectifying it into a low-frequency signal which is proportional to the carrier amplitude, and then this has audio-frequency components which are heard. This happens because you are producing such a strong RF field that PCB traces and wires in the audio equipment are acting as antennas and then semiconductor components inside are acting like diodes to rectify the RF. Sean On Sat, Dec 10, 2011 at 9:18 AM, V G wrote: > http://www.freesound.org/people/vtkproductions.com/sounds/40845/ > > That's what it sounds like. I hear it occasionally wherever I go, anywher= e > around the world. What frequencies/devices/protocols are causing it, and > what data does it represent? > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .