KVLY-TV mast, which is guy-wire supported.

A guy-wire or guy rope is a metal wire used to aid stability in tall structures (frequently radio towers). It is attached to a building on one end and the ground on the other. They are almost universally used in counter-balancing sets or pairs, with one wire on one side of the building, and one on the other.

A guy-wire is often placed at the end of a string of power poles to counterbalance the pull of the wires.

Roof antennas are usually held up by three guy-wires.

At some high constructions flight safety markers in the guys are necessary. For chimneys and masts for VHF-/UHF-transmissions or non-transmission use only the mechanical properties of he guys are important. This is not the case for mast antennas, for masts with aerials for VLF, LF, MF and SW or for masts situated close to such aerials.

Guys for mast antennas

Special attention must be paid for guys of mast antennas, because guys of conductive materials as metals can have a strong influence of the radiation pattern of the mast. Guys longer than a fifth of the radiated wavelength can have a significant influence of the radiation pattern, especially when the mast is used as mast antenna or carrying an aerial for VLF, LF, MF and SW, but also sometimes when it is situated close to such a site. At most mast antennas steel guys are used, which are divided by insulators in multiple sections, smaller than a fifth of radiated wavelength. As insulators steatite types are used. However these sections can show high levels of static electricity so at high masts very large insulators are required. For overvoltage protection in case of lightning strikes lightning arresters are required at the insulators, which had to be maintenained carefully, because insulator failures can lead to mast collapse. This maintenance work is especially at high structures sometimes very difficult. So there are often guys used at some newer mast antennas which are fixed with insulators at the mast construction and grounded via coils, which are situated next to the anchor blocks at which the guys are fixed on insulators. In some cases it is possible to ground the guys directly at the anchor blocks. However this is only possible, if the guys do not disturb the radiation pattern of the mast antenna. At some mast antennas guys of non-conductive polymeres are used. Although these guys seem to be the best choice for mast antennas they are barely used, because these guys do not have a long durability.

Especially at antennas for longwave and VLF the guys could also have an electrical function, either for capacitive lengthing of the mast or for feeding the mast with the radio power, which should be radiated. In these cases the guys are fixed without an insulator on the mast, but there is at least one insulator in the guy necessary. If guys are used for feeding the mast with high frequency power it is often possible to use a grounded mast. The guys are fed via conductor ropes running from the building with the tuning unit to the feesing point at the guys.

Guy structures

A list of famous guyed structures can be found on List of masts. There are also stuctures, which consist of a free standing bottom and a guyed top.

See also

• radio mast