Subcarrier

Sideband of a radio frequency carrier wave A subcarrier is a secondary carrier signal, derived from or frequency-related to a primary carrier, that is modulated to transmit additional information. Examples include the provision of colour in a black and white television system or the provision of stereo in a monophonic radio broadcast. There is no physical difference between a carrier and a subcarrier; the "sub" implies that it has been derived from a carrier, which has been amplitude modulated by a steady signal and has a constant frequency relation to it. FM stereo Stereo broadcasting is made possible by using a subcarrier on FM radio stations, which takes the left channel and "subtracts" the right channel from it — essentially by hooking up the right-channel wires backward (reversing polarity) and then joining left and reversed-right. The result is modulated with suppressed carrier AM, more correctly called sum and difference modulation or SDM, at 38 kHz in the FM signal, which is joined at 2% modulation with the mono left+right audio (which ranges 50 Hz ~ 15 kHz). Once the receiver demodulates the L+R and L−R signals, it adds the two signals ([L+R] + [L−R] = 2L) to get the