single-wire line

A single-wire line is an early form of telecommunications transmission where a single conductor, often iron wire, was used for sending signals. The return path for the electrical current was provided through the earth. This system was adequate for low-frequency telegraph signals but proved insufficient for higher frequencies, such as those used for speech.1

Single-wire lines suffer from significant signal loss (attenuation) over distance and are highly susceptible to interference from natural phenomena like lightning or man-made sources such as crosstalk from nearby wires. To overcome these limitations, telecommunications evolved to use two-wire systems, known as metallic circuits, which offered better signal integrity and reduced interference.123