You can use various methods to receive a digital television signal. To view the broadcast of satellite channels, equipment is used, located at the subscriber. It consists of an antenna in the form of a "plate" and a decoding receiver. Cable television involves placing the television signal receiver in a separate remote station.
The transmission of the received and decoded information to the consumer occurs along coaxial lines using amplifiers that compensate for the decrease in the signal level due to the wave impedance of the cable. A subscriber has to pay a monthly fee for the opportunity to take advantage of digital television. This need can be eliminated by installing a receiving antenna for terrestrial television transmitted by translators according to the DVB T2 standard. Under certain conditions, the use of antenna amplifiers for digital television is required.
Antennas for receiving digital television
Broadcast digital television in Russia is in the decimeter wave range. This corresponds to the wavelength of the received signal from 1 meter to 10 centimeters or the frequency range from 470 to 860 MHz.
The best reception is provided by antennas having the geometric dimensions of the 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 having indicators sufficient for high-quality viewing of digital television transmissions are used in settlements near transmitting television centers.
When television receivers are removed from translators (or repeaters) for more than 10 kilometers, external decimetric antennas are raised above the earth's surface to provide direct visibility to 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.
Amplifier Applications for Digital Television
Amplifiers of a television signal of the DVB T2 standard, when used together with a receiving antenna, are designed to improve image and sound quality on the screens of television receivers. The main gain of the useful television signal is provided by the antenna. Due to its directivity coefficient, it concentrates the power transmitted through the cable of the TV in the direction of the television translator. Signals received over the air from other directions are attenuated by the antenna. It has selective properties.
An antenna amplifier amplifies all components of the signal received by the antenna equally. Its use is advisable in the case of the external location of the receiving antenna for digital television DVB T2 at a considerable height. It allows you to compensate for the attenuation of the received antenna signal in the coaxial cable. These losses are estimated by the specific attenuation and are measured in units of dB / m. The longer the cable, the stronger the attenuation of the signal in it.
Main 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 corresponding to the finished product - the antenna plus the amplifier. The main technical characteristics of antenna amplifiers include the following:
- operating range (MHz);
- maximum gain in the operating frequency range (dB);
- noise figure (dB);
- input and output impedance;
- DC supply voltage (V).
The operating frequency range should be slightly wider than the decimeter range of (474-858) MHz. Broadcasting of digital television DVB T2 is carried out in multiplex packages (RTRS-1 and RTRS-2), each of which includes 10 television programs on the frequencies of one of the television channels. For different telecentres and repeaters, they can have different meanings.
The maximum gain is selected according to the length of the television cable used. The amount of linear attenuation depends on the type of cable and is (0.2-0.7) dB / m. The gain values of industrial designs reach 28-38 dB. A large gain does not always lead to an improvement in the quality of the television image in the case of digital television. It is better to have an antenna amplifier, which provides for the possibility of smooth adjustment of this parameter using an attenuator.
In a comparative evaluation of several samples, the choice should be stopped on the one whose intrinsic noise coefficient is of less importance. The level of the useful signal at its output will prevail over the level of interference and airborne noise to a greater extent. The range of this parameter for industrial products is (1.7-3.2) dB.
You should pay attention to wave impedances when choosing an additional stand-alone amplifier and making your own antenna amplifier for digital television. The transmission of the greatest power of the signal received by the antenna occurs when the input wave impedance of the amplifier and the output wave impedance of the antenna used are equal. Therefore, the parameters of the latter should be known. The output impedance should correspond to the impedance of the television cable and be 75 ohms.
The value of the DC power voltage indicates the possibility of using an additional 12 V power supply or the power of the antenna amplifier for digital television directly via the antenna cable from the 5 V digital decoding tuner. These data are indicated on the housing of the purchased stand-alone amplifier or active television antenna.
Overview of industrial active antennas and antenna amplifiers
Active factory-made antennas can be produced in the form of indoor structures having 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 signals of digital television. Vibrators are made in the form of open rings or frames. Elongated ellipses are complemented by horizontal metal strips or rods placed on a common traverse. Often on the body of the products there are elements of operational adjustment of the gain 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 insulation of elements from surrounding metal surfaces should be given increased attention. Reliable lightning protection should be considered.
Ways to connect antenna amplifiers
Built-in antenna amplifiers require DC power for their operation. Typically, the voltage is 12 V. In this case, the rectifier is included in the package of delivery of the active antenna.
It connects to the product using the connector on its body. In the case of the use of a stand-alone amplifier, the scope of supply includes a power injector or antenna separator. High-frequency connectors are connected by cable to the receiving antenna and the antenna jack of the digital tuner. Some active antennas are designed for the use of a 5 V DC supply voltage. It comes to them directly through the internal core of the coaxial cable from the antenna jack of a digital set-top box or TV with Smart TV support.
It is possible to use an additional USB-connector.
Homemade Antenna Amplifiers for Digital Television
It is worth noting that you can make antenna amplifiers yourself. In this case, it is 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 - gain, intrinsic noise level, range of operation - are determined by the properties of the active elements used.
Antenna amplifier circuits for digital television contain one or two amplification cascades made on low-noise bipolar transistors with their own gain of at least 200 units and with a cut-off frequency of at least 5-8 GHz. They usually have a miniature SMD housing design. The presence of bandpass filters in the circuits makes it possible to use the amplifying properties of active elements in the frequency range of transmitters of the DVB T2 standard.
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 those cases when using a passive antenna it is not possible to achieve high-quality reception of a digital television signal. After familiarization with the material presented in the article, an interested reader will be able to make the right choice of the model of the device he needs, focusing not only on the appearance, but also on its functionality, technical characteristics.