| Although the IR 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 ICs that are now
available, an FM receiver is easy to build, and contains little more circuitry than a
high-gain audio amplifier. |