Twin-lead

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Twin-lead is a two-conductor ribbon cable of 300 ohms characteristic impedance commonly used as a transmission line for balanced connection of television antennas.

It has the advantage that it can be connected directly to a suitably designed dipole, yagi or similar balanced antenna, and was almost universally used for feedlines to outside antennas in the days of black-and-white television. However for colour television installations it has been largely replaced by 75-ohm coaxial cable.

A 300-to-75-ohm balun, showing twin-lead on the right hand side

In domestic television installations, a balun with a 4:1 turns ratio is commonly used to match twin-lead to 75-ohm coaxial cable.

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