Guyed mast

A guyed mast is a tall thin vertical structure that depends on guy lines for stability. The mast itself has the compressive strength to support its own weight, but usually does not have the shear strength to stand unsupported, and requires guy lines, diagonal tensioned cables attached to the ground, usually spaced at equal angles about its base, to resist lateral forces such as wind loads and keep it upright.

Guyed masts are frequently used for radio antennas. The mast can either support aerials (for VHF and UHF) mounted at its top, or the entire structure itself can function as an antenna (for VLF, LF, MF); this is called a mast radiator. In the latter case, the mast needs to be insulated from the ground. Guyed radio masts are typically tall enough that they require several sets of guy lines, 2 to 4, attached at different heights on the mast, to prevent them from buckling. An exception was the Blaw-Knox tower, widely used during the 1930s, whose distinctive wide diamond (rhomboidal) shape gave it the shear strength that it only required one set of guys.