You can use different methods to receive a digital TV signal. To view the broadcast of satellite channels, equipment located at the subscriber is used. It consists of a dish antenna and a decoding receiver. Cable television involves placing a television signal receiver in a separate remote station.
The transmission of the received and decoded information to the consumer occurs via coaxial lines using amplifiers that compensate for the decrease in the signal level due to the wave impedance of the cable. The subscriber has to pay a monthly fee for the opportunity to use the benefits of digital television. From this need it can be relieved by the installation of a receiving antenna for terrestrial television transmitted by translators according to the DVB standardT2. Under certain conditions, the use of antenna amplifiers for digital television is required.
Antennas for receiving digital television
Digital television broadcasting in Russia is carried out in the decimeter wave range. This corresponds to a received signal wavelength of 1 meter to 10 centimeters or a frequency range of 470 to 860 MHz.
The best reception is provided by antennas with geometric dimensions of vibrators corresponding to ¼ wavelength. These include narrowly directed antennas of the "wave channel" type with a large number of transverse vibrators (directors), zigzag antennas with an additional reflector, log-periodic antennas.
Indoor antennas, which have indicators sufficient for high-quality viewing of digital television broadcasts, are used in settlements near transmitting television centers.
When television receivers are more than 10 kilometers away from broadcasters (or repeaters), outdoor decimeter antennas are used, raised above the earth's surface to ensure direct visibility of the transmitting antennas. In this case, it becomes advisable to use active television antennas with a built-in amplifier or an additional antenna amplifier. The choice of antenna for digital television DVB T2 is up to the user.
Application of amplifiers for digital television
TV signal amplifiers of the DVB T2 standard with theirwhen used together with a receiving antenna, they are designed to improve the quality of the image and sound on the screens of television receivers. The main amplification of the useful television signal is carried out by the antenna. Due to its directional factor, it concentrates the power transmitted through the TV cable in the direction of the TV broadcaster. Signals coming over the air from other directions are attenuated by the antenna. It has selective properties.
Antenna amplifier amplifies all components of the signal received by the antenna equally. Its use is advisable in the case of an outdoor location of the receiving antenna for digital television DVB T2 at a considerable height. It allows you to compensate for the attenuation of the signal received by the antenna in the coaxial cable. These losses are estimated by the attenuation per unit length and are measured in units of dB/m. The longer the cable, the stronger the signal attenuation in it.
Basic parameters of antenna amplifiers
If a decision is made on the need to use an amplifier, then you need to familiarize yourself with its parameters. It should be borne in mind that when buying an active antenna, the accompanying documentation indicates the values \u200b\u200bthat correspond to the finished product - the antenna plus the amplifier. The main technical characteristics of antenna amplifiers are as follows:
- operating band (MHz);
- maximum gain over operating frequency range (dB);
- noise figure (dB);
- input and output impedance;
- voltageDC supply (V).
The operating frequency range should be slightly wider than the decimeter range, which is (474-858) MHz. DVB T2 digital television broadcasting is carried out in multiplex packages (RTRS-1 and RTRS-2), each of which includes 10 television programs, at the frequencies of one of the television channels. For different TV centers and repeaters, they may have different meanings.
Maximum gain is selected according to the length of the TV cable used. The value of linear attenuation depends on the type of cable and is (0.2-0.7) dB/m. The gain values of industrial samples reach 28-38 dB. A large gain does not always lead to an improvement in the quality of the television picture in the case of digital television. It is better to have an antenna amplifier that provides the ability to smoothly adjust this parameter using an attenuator.
When comparing several samples, the choice should be made on the one with the lower noise figure. The level of the useful signal at its output will prevail over the level of interference and radio noise to a greater extent. The range of this parameter for industrial products is (1, 7-3, 2) dB.
Wave impedances should be paid attention to when choosing an additional stand-alone amplifier and making an antenna amplifier for digital television with your own hands. The transmission of the greatest power of the signal received by the antenna occurs whenthe equality of the input impedance of the amplifier and the output impedance of the antenna used. Therefore, the parameters of the latter must be known. The output impedance must match the characteristic impedance of the television cable and be 75 ohms.
The DC supply voltage value indicates the possibility of using an additional 12 V power supply or powering an antenna amplifier for digital television directly via the antenna cable from a 5 V digital decoding tuner. This data is indicated on the case of the purchased stand-alone amplifier or active television antennas.
Overview of industrial active antennas and antenna amplifiers
Prefabricated active antennas can be produced in the form of room structures that have a design that does not violate the general interior of the room in which they are installed. Their geometric dimensions correspond to the wavelengths of the received digital television signals. Vibrators are made in the form of open rings or frames. The elongated ellipses are complemented by horizontal metal strips or rods placed on a common traverse. Often on the case of products there are elements of operational gain adjustment of the built-in amplifier.
Outdoor antennas have a narrower radiation pattern. This is achieved by using a larger number of transverse elements (directors) and additional gratings (reflectors) located behind the main range vibrator. The quality of installation of outdoor active antennas,cable termination and isolation of elements from surrounding metal surfaces should be given increased attention. Reliable lightning protection should be provided.
Methods for connecting antenna amplifiers
Built-in antenna amplifiers require DC power to operate. As a rule, the voltage value is 12 V. In this case, a rectifier is included in the delivery of the active antenna.
It is connected to the product using a connector on its body. In the case of using a stand-alone amplifier, the delivery set includes a power injector or an antenna separator. The high-frequency connectors are connected by a cable to the receiving antenna and the digital tuner's antenna jack. Some active antennas are designed to use a 5 V DC supply voltage. It comes directly to them through the internal core of the coaxial cable from the antenna jack of a digital set-top box or a Smart TV.
Optional USB connector available.
Homemade antenna amplifiers for digital television
It is worth noting that you can make antenna amplifiers yourself. In this case, we are talking not only about profit, but also about interest. Despite the fact that the price of antenna amplifiers for digital television today is quite affordable for the average user, many enthusiasts continue to design them. Their main parameters are gain, levelown noise, operating range - are determined by the properties of the active elements used.
Antenna amplifier circuits for digital television contain one or two amplification stages, made on low-noise bipolar transistors with an intrinsic gain of at least 200 units and with a cutoff frequency of at least 5-8 GHz. They usually have a miniature SMD body design. The presence of band-pass filters in the circuits makes it possible to use the amplifying properties of active elements in the frequency range of DVB T2 transmitters.
Customer Reviews
Many positive reviews come from users who use amplifiers from manufacturers such as Locus (LA, LV series), Alcad, domestic Remo and Planar to improve the quality of digital television reception.
Using an amplifier from Alcad allows you to connect several consumers to one antenna due to the high gain and the presence of an antenna output divider.
Conclusion
The use of an active antenna or a stand-alone antenna amplifier is justified in cases where a passive antenna cannot achieve high-quality digital television signal reception. After reading the material presented in the article, the interested reader will be able to make the right choice of the model of the device he needs, while focusing not only on the appearance, but also on its functionalfeatures, specifications.
