Currently in every home there is one orseveral tvs. An antenna is needed to organize the broadcast of television signals. There are many types of receivers. They are divided by purpose, type of received signals, shape, size, and so on. The subject of our conversation today will be receiving television antennas.
Each of us in our lives in one way or anothercame across these devices. A television antenna is a metal structure, most often of aluminum, designed to receive a radio signal. Depending on the type of received television range, they are divided into meter and decimeter devices. They are also divided according to the place of installation for indoor and outdoor use. By the method of receiving a signal, a television antenna can be active or passive.
Consider the main types of receiving devices:
1. Dipole or split vibrator.They are quarter-wave, half-wave and wave. In the latter, the length of the vibrator corresponds to the wavelength of the signal that is received; half-wave - half of the signal; and, respectively, in the quarter-wave - a quarter. In a dipole, the characteristic impedance is 300 ohms, in order to match the antenna with the TV and the receiving cable in amateur conditions often use a matching half-wave loop. For all teleantenna, the drop cable has a characteristic impedance of 75 Ohms. A dipole, in fact, is an analogue of a room antenna.
2.The television antenna of the “wave channel” type can be: two-element, three-element, five-element, seven-element, eleven-element and sixteen-element. Loop vibrator is not used by itself, it is an active element for antennas of this type. Antenna "wave channel" consists of an active element (vibrator, usually loop) and passive elements: a reflector and directors mounted on a common boom. The director is a passive vibrator located in front of the active vibrator. Reflector - vibrator, located behind the active. For antennas of this type there is one drawback: when adding passive elements to a wave vibrator, the input impedance of the antenna decreases. Receivers of this type are widely distributed in radar and radio communications devices.
3.Log-periodic television antenna is a broadband device that provides reception of signals in the frequency range (decimeter and meter waves). In the working range, optimum matching of the antenna and feeder is achieved, while the gain remains constant.
4.Frame television antennas are designed to receive signals, in cases where the "wave channel" antennas are not able to provide satisfactory signal quality. Represent a double or triple square. Devices of this type combine high gain and simplicity of design, do not require adjustment.
5.Common-mode arrays are a complex directional system consisting of weakly directional antennas that are spaced apart; they are arranged in such a way that the phases of the signals are the same. As a rule, they are assembled from identical antennas arranged in several rows and connected to an electronic unit. Common mode receivers are television antennas with an amplifier.
In conclusion, we say that the choice of the antenna must be approached individually, depending on local geographic conditions, on the installation site and on the desired result.
