Currently, every home has one or more televisions. To organize the broadcast of television signals, an antenna is required. 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 his life to some extent faced with these devices. A television antenna is a metal structure, most often made 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 into indoor and outdoor use. According to the method of receiving the signal, the television antenna can be active or passive.
Let's consider the main types of receivers:
1. Dipole orsplit vibrator. They are quarter-wave, half-wave and wave. For the latter, the length of the vibrator corresponds to the wavelength of the signal that is received; for half-wave - half the signal; and, accordingly, for quarter-waves - quarters. The dipole has a wave impedance of 300 ohms, in order to match the antenna with the TV and the receiving cable in amateur conditions, a matching half-wave loop is often used. For all television antennas, the drop cable has a characteristic impedance of 75 ohms. The dipole, in fact, is an analogue of an indoor antenna.
2. A television antenna of the "wave channel" type is: two-element, three-element, five-element, seven-element, eleven-element and sixteen-element. The loop vibrator is not used on its own, it is an active element for antennas of this type. The "wave channel" antenna consists of an active element (a vibrator, more often a 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 - a vibrator located behind the active one. Antennas of this type have one drawback: when passive elements are added to the wave vibrator, the input impedance of the antenna decreases. Receivers of this type are widely used in radar and radio communication devices.
3. A log-periodic television antenna is a broadband device that provides reception of signals in the frequency range (decimeter andmeter waves). In the operating range, optimal matching of the antenna and feeder is achieved, while the gain remains constant.
4. Loop television antennas are designed to receive signals in cases where the "wave channel" antennas are not able to provide a satisfactory signal quality. Represent a double or triple square. Devices of this type combine high gain and simplicity of design, do not require tuning.
5. In-phase arrays are a complex directional system consisting of weakly directional antennas that are spaced apart in space, they are located 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, let's say that the choice of antenna must be approached individually, depending on local geographical conditions, on the installation site and on the desired result.
