A t-aerial is a type of antenna that transmits and receives television and radio signals. It gets its name from its design which consists of a horizontal wire suspended some distance above ground with a trailing wire leading downward, forming the shape of the letter "T." The ability of a t-aerial to transmit or receive signals is affected by a number of factors including the resistance of the wires, their lengths, and the ratio of those lengths. The wavelength of the signal to be transmitted or received matter as well. A t-aerial can be a simple design with one horizontal and one vertical wire or it can incorporate additional wires at the top. It might also have a radial pattern of buried wires at the bottom of the vertical wire.
The simplest and most basic t-aerial consists of just two wires, one horizontal and one vertical. The vertical wire is connected at its base to the transmitter or receiver. The horizontal wire is connected to the vertical wire and suspended above the ground, usually supported on each end by a pole or tower, structures called masts. The horizontal wire must be well insulated from the support towers. The thickness, or gauge, of the wires as well as their length is influenced by the frequencies which are to be transmitted or received.
Transmission of medium and long wavelength signals is the primary usage of t-aerial antennae. A simple vertical antenna is the ideal for transmitting and receiving those wavelengths, but in situations where a very tall vertical antenna is not practical, a t-aerial is often a good alternative. Engineers and electronics enthusiasts have a series of formulas to calculate ideal the dimensions of the wires. Generally, more than one configuration is possible for maximum efficiency, and the dimensions that are easiest to construct are usually chosen.
Any given t-aerial could give the same performance with a several other possible configurations for the two wires. One example of a popular t-aerial design is built using a vertical of 11 m (36 ft) and a horizontal of 50 m (164 ft). The same performance can also be achieved by a t-aerial in which the horizontal and vertical wires are nearly the same length — the vertical measuring 23 m (75 ft) and the horizontal measuring 23.5 m (77 ft).
Other modifications of the basic t-aerial design include additional wires at the top of the aerial that are connected to and run parallel to the horizontal wire. This arrangement is commonly called a cage. A series of wires may be attached to the bottom of the vertical wire as well. These wires are called radials because they extend out from their connection with the vertical wire in a radial pattern like the spokes of a wheel. Radial wires are usually buried in the ground.