A secondary, lower-frequency signal that is modulated onto a primary carrier wave alongside the main baseband signal. Broadcast engineers use them to piggyback extra audio channels, telemetry, or metadata onto a single transmitter allocation without interfering with the primary broadcast. When the receiver demodulates the main carrier, it extracts the subcarrier and then demodulates it separately to recover the hidden data.
The station transmits its main audio in stereo, but they lease out an SCA subcarrier to a background music service.
Related terms
Frequency band
A defined contiguous range of radio frequencies allocated for a specific purpose.
Baseband
The original frequency range of a transmission signal before it is modulated onto a higher-frequency carrier wave.
OFDM
Orthogonal Frequency Division Multiplexing, a digital transmission method using multiple subcarriers.