Let us briefly describe the remarkable qualities of digital television. The technology differs from the traditional form of the broadcast signal. Analog systems change the field strength continuously, digital each pixel value is encoded with ones, zeros. Indoor digital television antenna receives any signal. Receiving coding is indifferent, polarization plays a decisive role.
The reason for mastering digital broadcasting
The digital signal is very stable. Units and zeros are sometimes additionally encrypted with a code known by the recipient. Against the background of the noise, the equipment is scanning the received signals, the correspondence of the sample to the incoming wave gives a peak many times higher than the noise level. Digital broadcasting will allow transmitter power to be reduced.
It is clear that quality is very important in conditions of increased background of electromagnetic radiation. This explains the obvious fact: digital television is gaining popularity.
We will discuss quality separately. The encoded signal conveys the colors of the pixels for sure. The picture looks real, analogous indicators are difficult to achieve using an analog transmission. Billions of colors can be recognized by the signal received by the antenna for digital television. You may not notice the difference on the screen just because it is not profitable for free channels to increase the cost of equipment, buying a double frequency band in order to please the user with the Brilliant Color system.
Digital Television was able to narrow the signal spectrum. The physical meaning of the spectrum is discussed. The fact of conversion means: previously there were 10 analog channels, now there will be about 35 digital standard definition.
There are three side properties that are useful to both sides of the bundle of client-provider properties:
- Protection of the channel from viewers who have delayed the subscription fee. A valuable plus given by digital television aerials. See the right, cutting off the excess.
- Integration of Internet broadcasting. Now it is permissible to use special provider keys without buying additional equipment( receiver).The satellite access code is transmitted by the service provider's Internet network. Usually there is a free test mode for watching satellite digital television.
- Innovation of video playback technologies is interactive. Digital options issued by DVD, live.
A dozen of advantages are shown on digital TV antennas. If logical arguments do not convince you to choose a number, you should know: by 2015 it was planned to make 100% of the broadcast digital.
Why not use conventional antennas
Wide-band devices understate the gain by catching a larger frequency spectrum. Not always the lack of catastrophe turns. Residents of problem regions with a weak signal will have to think about it.
Signal Polarization
Constant electric field is not transferred by the ether. The property of mobility is characterized only by dynamic systems. The world allows a change in the electric field to cause an adequate magnetic response. It turns out a wave resembling a Christmas garland of twisted, cut along the paper. Narrows and expands.
Electromagnetic wave, fix the phenomenon of the human eye, looks like. Two school sinusoids, mutually perpendicular. The first chose a horizontal plane, the other - a vertical one. One is the amplitude of the electric field, the other is magnetic. Polarization can be divided:
- Vertical.
- Horizontal.
Polarization is characterized by a spatial figure describing the amplitude vector of the electric field. Owners of smart TVs catch the plane horizontal, or vertical( radio).Digital broadcasting uses the simplest waveform.
The entire polarization formation process is performed by the transmitting antenna. Reception must have equivalent characteristics. Identity is called electromagnetic compatibility.
The case is not limited to this case, the spiral antennas have circular polarization, right-left. Determined by the direction of twisting the coils. Spiral antennas are incompatible with linear ones.
Elliptical polarization occurs, circular is considered a special case. You see - simple information. It remains to add - the amplitude vectors of the electric, magnetic fields do not occupy perpendicular to the plane, continuously rotating. It resembles the image of a human DNA chain.
Frequency Band Consider the concept of frequency. Schoolchildren saw a sine wave. The period of the function is contained in the denominator, the unit is the numerator, together we get the frequency. Shows the rate of change of the amplitude of the electric, magnetic fields. Occupy perpendicular planes. Circular polarization is characterized by frequency, the dependence is more complicated.
Real signals differ from sine wave. A small time interval allows us to consider the field approximately( short time).The real satellite signal takes a fixed frequency range. The result is summed up by the addition of elementary harmonics( sinusoids).The graph represents the process of the dependence of the amplitude of a single sinusoid( volts) on the frequency( Hertz).The representation is called the signal spectrum occupied by the horizontal segment - the signal bandwidth. Add - in digital television, the harmonic separates a strictly defined distance. The spectrum is discrete.
Antenna for receiving digital television is characterized by polarization, frequency band. Cannot use arbitrary modification. One antenna cannot cover the frequency band occupied by digital television.
Digital Broadcasting
Digital broadcasting is satellite, terrestrial, cable. Today the second type of television is affected. The satellite signal is received by parabolic, toroidal antennas.
The nominal broadcast frequencies are prescribed by GOST 7845-92.According to the manuscript, digital television set aside 5 bands. Stacked in the range of 48 - 790 MHz. This span corresponds to sixty channels. Antennas for digital terrestrial television may cover this list 100% or catch one broadcast, VHF or UHF.
Standard clearly indicate carrier frequency for image and sound. Polarization in digital TV antennas is horizontal, but the standard regulates the use of vertical polarization. But in any case, linear. Image carrier is modulated in amplitude, and sound in frequency. In this digital television is not far removed from the analog. The lower sideband is suppressed to save energy and narrow the bandwidth of the paths of the transmitting and receiving devices.
For device connections, it is prescribed to use a 75 Ohm coaxial cable. Accordingly, the input and output impedances of the devices are close to this value.
Antennas
Antennas for digital television follow the requirements outlined in the previous section. Available models:
- room;
- street;
- hybrid.
Which antenna for digital television will be needed, it is relatively easy to choose. If the repeater is outside the window, then the room option is preferable. It is enough to purchase a couple of meters of coaxial wire, and this is enough for the installation of equipment. Indoor antenna costs less, has a stand, often the instruction allows to be placed near the window.
Outdoor options are required where the signal is relatively weak. On the roof reception is incomparably better, and this fact is permissible to use to enjoy digital broadcasting. There were no passive antennas for the street, but if they exist in nature, then it is worth considering that the signal level at the input of the TV will strongly depend on the cable length. Living on the second floor, most likely need an active antenna.
Hybrid options allow you to install yourself in the room and on the roof without sacrificing quality. Well, the price, of course, will be higher than that of the room one.
When you choose your equipment for receiving the signal, see that the antenna and broadcast bands coincide. Check the latest information with your digital television provider. Produced as a variety of overlapping channels entirely, and selective antennas.
NPP Ost manufactures an attractive product for Russians. Delta is an antenna for digital television, but looking for products through Yandex is a bad thing. The St. Petersburg manufacturer distributes products through dealers. And in the presence of everything that is only needed by the consumer.
Moreover, on the counter there are any versions from the point of view of installation sites, so also the constructive shines with diversity. The basis of the logarithmic and framework elements, but the external form is so amazing that the site is recommended to go at least with the aim to just admire this magnificence. Impresses with a wealth of engineering solutions. Not in the example of foreign products that are for one person.
Self-taught people have chosen the simplest method of manufacturing devices. The material is chosen coaxial cable. Use a TV impedance of 75 ohms. Enough to ensure reliable reception of a single broadcast frequency. Three multiplexes are available to Muscovites, the spectrum is constantly expanding.
Good luck! Read our reviews, watch digital TV.
