Modulation

Remote controls use one of two fundamental types of modulation, AM or FM, although there are several variations on the fundamental types.

The above links refer to modulating a carrier with an audio signal. With remote controls, the carrier is almost always modulated by a digital signal taking the form of a square wave that encodes bitwise information by varying the durations of pulses, spaces, both pulses and spaces, by a phase change at the midpoint of each bit's timeframe or by varying the carrier frequency.

Some form of AM is most widely used. Variations may be called ASK (Amplitude Shift Keying), OOK (On/Off Keying), or CPCA (Carrier Present, Carrier Absent).

Digital FM is called FSK (Frequency Shift Keying) and involves two different carrier frequencies to denote two different states.

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