An apparatus is provided for high frequency multiplexed electrical line communication
for cable TV, telephone, internet, security and other control applications over
the mid and low voltage power lines and directly through the transformers. The
apparatus includes a transmitter, a receiver, a modem, a multiplexer and multiple
couplers at each of two or more locations along an electrical line. The couplers
have capacitive circuits serially connected with an air-core or dielectric-core
transformer. The capacitive circuits resonate with the transformer at a preselected
frequency. The coupler eliminates noise and is matched to the characteristic impedance
of the line at the preselected frequency, which linearizes communication on the
line and allows high speed data and voice communication over long distances. Multiple
modulators and demodulators are used to produce multiple modulated carrier frequencies.
