On 5/26/2011 1:30 PM, Alan Bloom wrote: > TDMA (time division multiple access) cell phones share a frequency > channel by transmitting only in certain time slots. The power is pulsed > on and off even though the modulation mode may be constant-power.
Yes. For at least one of the commonly used standards, the repetition rate is about 218 Hz, which puts the harmonics of the detected square waves right in the middle of the audio spectrum, and thus highly audible. Once you know what it sounds like, you will sometimes hear bursts of digital hash at public events, when the cell phone of a public figure gets close to a piece of audio gear with a pin one problem. This used to be a LOT more common than it is now -- mfrs of mics and other audio gear started taking pin one problems and RFI a LOT more seriously when Blackberrys came on the scene bigtime (and reportedly gave a Blackberry to every member of congress and their staff). The senator would lean the Blackberry up against the tube holding the microphone in front of him, and the Blackberry would couple into the mic wiring. It was so bad that they had to shut down hearings until they eventually found and purchased mics without pin one problems. I consulted on that problem, both with the system designer and two mic companies. 73, Jim Brown K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
