of some automation standards.

Low-speed narrow-band

Narrowband power-line communications began soon after electrical service became widespread. Around the year 1922, the first carrier frequency systems began to operate over high-tension lines with frequencies of 15 to 500 kHz for telemetry purposes, and this continues. Consumer products such as baby alarms have been available at least since 1940.

In the 1930s, ripple carrier signaling was introduced on the medium (10-20 kV) and low voltage (240/415 V) distribution

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