Digital television (DTV) uses the formation of a television signal, its transmission and processing in digital form. Information words, images and sound are transmitted in the form of an encoded sequence of “1” (units) and “0” (zeros). Such a transmission system allows to provide a high degree of protection against external interference, to obtain high image quality compared to analog television. In addition, when using DTV, the capabilities of televisions embedded in them by developers and creators of television technology are fully realized.
Digital TV Transmission Methods
By transmission method is meant the option of delivering digital television signals to a subscriber. Based on this, the following types of DTV standards have been developed and are currently adopted by an international organization:
- DVB-T - digital terrestrial television, for the transmission of signals which is used radio meter or decimeter wavelength range;
- DVB-T2 - an improved type of transmission of a television signal of the previous standard (2nd generation);
- DVB-C - cable television using MPEG-2 image and sound coding;
- DVB-C2 - the second generation of the previous standard, using methods to increase its noise immunity;
- DVB-S - digital satellite broadcasting;
- DVB-S2 is an advanced modification of the previous standard.
In addition to the listed options for providing digital television, Internet providers offer users the IPTV service, which allows you to receive streaming digital television using fiber optic cable lines or over the air of cellular operators. You can find out how to connect a digital TV in the following sections of the article.
Digital cable tv
A DTV signal is generated at the base station of the operator. It has powerful satellite digital television receivers. The information they received (image and sound) is encoded and compressed, and in this form is transmitted via cable lines of the fiber optic network of the regional operator to distribution panels in the homes of subscribers. In apartments, the input is carried out with a television coaxial cable RG-6 with a wave impedance of 75 ohms.
To install digital television consumer equipment must have a separate decoder. It converts the input signal into a form understandable to a television receiver. The operator provides the subscriber with the opportunity to purchase a decoder for a fee.
The digital tuner (decoder) incorporates most modern TVs. For cable television, it must support the DVB-C / C2 standard. This can be found in the documentation for the TV. In this case, to view all closed channels, the user will need a special CAM module. After connecting a paid access smart card to the tuner or CAM module slot, you can install digital television and tune into the channels provided by the selected operator.
A television broadcast satellite receives signals from terrestrial transmitting centers. It moves in a geostationary orbit at an altitude of about 36,000 km from the Earth. A certain area of the territory is constantly located in its visibility zone. Using transponders (transponders), the encoded signal is emitted back to the earth's surface, where it enters the narrowly directed antennas of DTV subscribers.
To install digital television, it is assumed that the user has the appropriate equipment:
- an antenna mirror (dish) in the form of a truncated paraboloid with a diameter of 0.6–0.9 meters, focusing the radio waves of the satellite transponders;
- Converter - a receiving device located on the bracket in the focus of the antenna;
- a tuner (decoder) that converts the signal received from the converter from a satellite of the DVB-S / 2 standard;
- smart card of the selected DTV operator.
In the case of using a TV with a built-in DVB-S / S2 tuner and a CAM module, the use of an additional set-top box (decoder) is not required. The converter is connected to the set-top box or TV with an RG-6 coaxial cable with high-frequency F-connectors at the ends. The set-top box is connected to the TV with an HDMI cable or “tulips”. The installation of an antenna for digital television requires the participation of the technical service of the DTV operator. The smart card is inserted into the slot of the decoder or CAM module. Which provider has the best digital television - the answer to this question should already be known to the user of the selected card.
Broadcast Digital TV
For transmission and reception of digital terrestrial television signals, the decimeter wavelength range is mainly used. In Russia, it corresponds to frequencies of 470–790 MHz or 21–60 television radio frequency channels. Installation of digital television is possible if the consumer has equipment that includes:
- a decimeter-wave antenna that receives a signal from a television center;
- a DVB-T2 tuner that converts the encoded input signal from the antenna into a form intelligible to a television receiver;
- TV for high quality picture and sound.
If a consumer uses a TV that has a tuner (decoder) of the DVB-T2 standard, an additional set-top box is not required. A high-quality digital television subscriber has 20 television channels available. They are combined into 2 multiplexes (10 channels each). Each multiplex is broadcast by its transmitter on one radio frequency channel. The frequency of the channel depends on the geographical location of the receiving location. There are special digital coverage maps for the entire country with detailed information.
Starting in January 2019, almost the entire country is gradually phased out to “digital” with the analogue broadcast transmitters turned off (regional broadcasting centers temporarily make exceptions). Watching digital channels of two multiplexes does not require a monthly fee for viewing them.
Digital Channel Setup
Before tuning, the antenna is connected to the high-frequency jack of a set-top box or TV. In the case of using a decoding set-top box, it is connected by a set of cables "tulip" with the inputs of a television receiver. The use of a cable with HDMI connectors is most preferred. It provides high-definition multimedia and stereo with presence. The console and TV are controlled by different remote controls.
To configure DTV channels using the remote control, the “Auto Search” mode is selected in the device settings menu. Channels will be determined not by one, but immediately by dozens. The search will take time (up to several minutes). Found channels must be fixed by pressing the corresponding button. If the auto search result is unsatisfactory, which may be an insufficient signal level at the receiving point, you must use the manual tuning mode by selecting the appropriate menu item.
Pressing the “Info” button on the remote control allows you to check the intensity and quality of the signal on the screen. Satisfactory are considered their performance at the level of more than 60%. If these requirements are met, then the digital channels on the TV can be considered complete.
Antennas for Digital Television
The design of the antenna used does not determine how the television signal is generated. The geometric dimensions of its elements should be commensurate with the wavelength at which it is being designed. Therefore, on digital antennas, you can see videos and read messages exclusively advertising. All digital television antennas are designed to receive decimeter wave radio signals.
Antennas may have a circular pattern. Such devices can be successfully used in the immediate vicinity of the transmitting center at a direct line of sight distance of no more than 3-5 km. They are usually issued in room execution.
Their vibrators are made in the form of telescopic pins capable of changing their length. Vibrators have the ability to orientate in space to obtain the most confident and high-quality reception in an urban environment. Vibrators are added in the form of rings of a strictly defined diameter.
What is needed for digital television in the country? The suburban option involves a significant removal of the TV from the transmitting centers. Therefore, to obtain a “digital” picture on the screen is possible only through the use of narrowly directed antennas with a large coefficient of own gain.
Often you have to use active antennas or use additional signal amplifiers. It is important not to forget that for digital television in the country you must also use the mast, which increases the direct visibility of the transmitting television center or repeater.
Factors Affecting Image Quality
The quality of the matrix of the television screen and the technology by which it is made have the greatest influence. From the old analogue TV, to which it was possible to connect a set-top box (decoder) to receive a digital signal, you can only receive the fact of receiving a television broadcast program. The quality of the picture will remain the same. Interference during reception will not be displayed on the screen in the form of “dashes” or “snow”. The image is either present or it will be replaced by an inscription on the “No Signal” screen.
The highest indicators today have LCD matrices with LED backlighting, as well as OLED, to create cells of which organic light-emitting diodes are used.
After reading the material presented in the article, the reader will understand that the advantages of digital TV over analog are obvious. We must accept the fact that the transition has practically taken place for objective reasons. The reader will now be able to select the equipment competently, depending on how he is going to receive the digital image.