Simplex signaling (SX) is
signaling
In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...
in which two conductors are used for a single
telecommunication circuit, and a center-tapped coil, or its equivalent, is used to split the signaling current equally between the two conductors. The return path for the current is
through ground.
It is distinct from a
phantom circuit in which the return current path for power or signaling is provided through different signal conductors.
SX signaling may be one-way, for intra-central-office use, or the simplex legs may be connected to form full-duplex signaling circuits that function like composite (CX) signaling circuits with
E&M lead control.
Simplex is also used to describe a powering method where one or more signal conductors carries direct current to power a remote device, which sends its output signal back on the same conductor.
Phantom powering as used in
audio is a form of simplex powering, as the return current flows through the ground or shield conductor.
References
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Telephony signals
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