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An inverted L antenna is a simple type of antenna that can be used to send or receive at a wide range of frequencies. The antenna consists of a length of horizontal wire which is suspended above the ground and another length of wire that descends from the horizontal wire to the ground. The simplicity of this antenna and the ease of constructing one at home makes it popular choice for personal use.
The horizontal component of the antenna is strung between two supports, which can be two free standing posts, or a post and the side of a house or other building. The two ends of the wire do not have to be even for the antenna to function properly, though each end does need to be insulated from the two supports. The antenna is more effective at picking up electromagnetic signals if it is strung at least 9 feet (3 meters) off the ground.
On one end of the horizontal component of the inverted L antenna, another length of wire is dropped from the antenna to the ground. This vertical section of the antenna is called a downlead and should be properly grounded. It is used to connect a receiver or transceiver to the antenna. The addition of this length of wire makes the antenna look like an inverted L.
Copper or insulated copper wire are common materials used to construct an inverted L antenna. The wire needs to be at least 9 to 15 feet (3 to 5 meters) long in order to receive signals in a useful range of wavelengths. Longer antennas will receive a wider range of signals, so it is useful to know what the desired range is before deciding on the length of the inverted L antenna.
The antenna impedance generated by an inverted L antenna is not usually the same as that of a coaxial cable. To use an inverted L antenna as a television receiver, it is necessary to use a converter to keep the signal from deteriorating as it travels from the antenna into the coaxial cable. With the use of a converter, the signals picked up by this type of antenna can be easily transmitted to a television.
In addition to its use as a receiver, the inverted L antenna is also commonly used to send signals. Sending signals through this type of antenna requires the use of a ground. Unless the antenna is grounded properly, the signals may be subject to a great deal of interference and can deteriorate rapidly.