SSB

Single sideband (SSB) is a radio transmission method that removes the carrier wave and one of the two identical sidebands produced during amplitude modulation, leaving only the modulated information on a single sideband. A standard AM signal wastes spectrum: the carrier carries no information, and the upper and lower sidebands are mirror images of each other. SSB strips both, keeping only one sideband and the essential data it carries, so the signal occupies roughly half the bandwidth of conventional AM.

In power systems and utilities, SSB appears in pilot-tone and ripple-control signalling schemes used for load management and remote switching. A control centre transmits an SSB signal at a low level on the power line itself, or via dedicated voice channels on microwave links, to communicate with substations and demand-response equipment across the network. The narrow bandwidth means multiple SSB channels can coexist without interference, and the suppressed carrier reduces power consumption on the transmitting end, which matters when the signal travels hundreds of kilometres.

The trade-off is complexity. Generating SSB requires precise filtering to remove the unwanted sideband, and receiving it demands a local oscillator locked tightly in phase and frequency; if that oscillator drifts, the demodulated audio becomes unintelligible or distorted. Standard AM is simpler and more forgiving, which is why it persists in broadcast radio. But in utility communications, where bandwidth is scarce and transmitter efficiency matters, SSB's advantages outweigh the receiver cost and maintenance burden.

SSB is less common in utilities today than it was in the 1970s and 1980s; digital signalling over dedicated SCADA networks and fibre has taken over much of that role. However, older SSB voice circuits and some ripple-control systems remain in operation, particularly in rural areas where dedicated infrastructure is uneconomical. Technicians must still understand SSB demodulation, tuning, and troubleshooting to maintain these legacy systems.