Currently, each house has one or more televisions. To organize the broadcast of television signals, an antenna is needed. There are many types of receivers. They are divided according to purpose, type of received signals, shape, size and so on. The subject of our conversation today will be the receiving television antennas.
Each of us in our life has, to one degree or another, come across 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 television range received, they are divided into meter and decimeter devices. They are also divided at the installation site for indoor and outdoor use. According to the method of receiving the signal, the television antenna may be active or passive.
Consider the main types of receivers:
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; in half-waves - half the signal; and, correspondingly, for quarter-wavelengths - quarters. At the dipole, the impedance is 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 wave impedance of 75 ohms. A dipole, in fact, is an analogue of a room antenna.
2. A television antenna of the “wave channel” type happens: two-element, three-element, five-element, seven-element, eleven-element and sixteen-element. The loop vibrator is not used independently; it is an active element for antennas of this type. The “wave channel” antenna consists of an active element (a vibrator, often a loop) and passive elements: a reflector and directors mounted on a common boom. A director is a passive vibrator located in front of an active vibrator. Reflector - a vibrator located behind the active. 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 widespread in radar and radio communication devices.
3. Log-periodic television antenna is a broadband device that provides signals in the frequency range (decimeter and meter waves). In the operating range, optimal matching of the antenna and feeder is achieved, while the gain remains constant.
4. Framework television antennas are designed to receive signals in cases where the antenna "wave channel" is not able to provide satisfactory signal quality. They are 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 in space, 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 the electronic unit. Common-mode receivers are television antennas with an amplifier.
In conclusion, we say that the choice of antenna must be approached individually, depending on local geographic conditions, on the installation location and on the desired result.