Posted on Mar 20, 2013 11855
Although theIR region is free from radio interference, it is subject to interference from incandescent lamps, fluorescent lamps, stray reflections, and other sources. A simple way to overcome that problem is to create a carrier by chopping the IR radiation at a rate of 100 kHz. The audio then modulates the carrier by modulating the chopping rate. A receiver then detects the IR beam as a 100-kHz FM signal.
The only disadvantage is that instead of a simple audio amplifier, a high-gain FM receiver is necessary. However, with the !Cs that are now available, an FM receiver is easy to build, and contains little more circuitry than a high-gain audio amplifier. The kit is available from North Country Radio, P.O. Box 53, Wykagyl Station, NY 10804.