On Mon, Mar 17, 2003 at 03:13:46PM +0100, Thomas Shaddack wrote: > Using a powerful high-frequency modulated infrared source (eg, a bank of > LEDs) located on a highly visible place, it couldbe possible to facilitate > local community broadcasts, effectively sidestepping all FCC regulations.
Hi, I don't know if this may be of interest to you, since it's related more to electromagnetic emanation monitoring, but anyway... in September 1999, I've used the modulation of keyborard's VLED as a means to broadcast data from a personal computer to the outside world. I've builded a very simple protocol by encoding data (in the basic version) through different LED's states. The bitrate was very low and obviously related to the specific chosen encoding. Infact, I've tried several encodings (e.g., some inspired to BAUDOT). However, the monitoring of the electromagnetic emanation was based on the "relative" radio frequencies and not on the visible spectrum. The monitoring equipment was very simple. A common radio receiver with audio cassette recorder. It was possible to tap the data by tuning the radio receiver, expecially on the following frequencies: LW 209 Khz, LW 201 Khz, MW 892 Khz. (the receiver was very simple and the maximum distance from the emission source was ten metres). The decoding of the recorder signlas was straighforward using FFT. ciao, alfonso
