Analog signal. What is the difference between cable television and digital television and which is better?
The difference between digital and analogue television is most easily illustrated by the differences between digital and analogue audio or photography. If in analog the television picture and sound track are encoded using an analog electrical signal, then in digital, accordingly, digital encoding is used.
At the end of the 90s, only analog color television existed in our country. The broadcast used the French SECAM coding system. Older readers probably remember that on video cassettes one could find films encoded using alternative systems - PAL or NTSC, for comfortable viewing of which a VCR with their support was needed.
To watch digital TV on a computer, all you need is a small USB module and a UHF antenna
The main disadvantages of the analogue are poor protection against interference, as well as a fairly wide band of the radio frequency spectrum required for transmitting one channel.
Therefore, on air we were limited to a maximum of two dozen color channels, and on cable networks an average of 70 (with rare exceptions).
If the TV is not equipped with a digital channel receiver, then you can buy a separate decoder that supports the DVB-T2 standard With an analog signal, it is quite difficult to create a service convenient for the user and operator (with the ability to quickly connect/disconnect channel packages, etc.). In addition, analog needs high-power transmitters with a large coverage area because Receivers need a high signal level to get a good picture, which means that the frequency spectrum on the radio is used very irrationally: in neighboring territories it is impossible to transmit on the same channel, competent frequency planning is required.
A digital signal does not have these disadvantages. The main advantage of digital is that the encoded channel can be compressed using modern algorithms (for example MPEG). Exactly how to encode a signal and how to compress it is determined by the standard. Today in Europe and Russia the main family of standards is DVB - the brainchild of the international consortium DVB Project.
The family includes standards for satellite, terrestrial, cable and mobile television, differing in the degree of compression, noise immunity and other parameters (important, depending on the transmission medium used). However, in the press, “digital” has recently been most often referred to as the terrestrial standard (in the case of Russia - DVB-T2). Let's start with it.
From analog to digital on air: Russian version
Given the advantages of digital, the world community began the transition to modern broadcasting standards in the early 2000s. In all countries, this process went on (and continues to go on) simultaneously with the “optimization” of radio air, which is actively used not only by television broadcasters, but also by mobile operators, the military and other consumers.
Due to compression into 1 analogue television channel, for example, in the DVB-T2 standard, it allows you to fit up to 10 digital channels with approximately the same picture quality. In addition, part of the spectrum frees up the aforementioned reduction in transmitter power. Within one country, these processes are regulated by the state, and on a continental scale - by various interstate agreements.
According to one such agreement, Russian border areas must eventually stop broadcasting in analogue format. So the transition from analogue to digital television determines not only the desire for new technologies, but also responsibility to our closest neighbors.
Inexpensive USB adapters for receiving digital channels can be found not only for PCs... 
...but also for smartphones and tablets. At the same time, they will be connected via micro-USB The transition from analogue to digital television on air in our country began in 2009. At that time, the DVB-T standard, which had already been implemented in a number of European countries, was taken as the basis.
You need to understand that television is a chain of interaction between a whole list of intermediaries between the content producer and its consumer, each of whom has a fleet of analog equipment that needs to be replaced. The state project involves updating only part of this chain - distribution and transmission equipment.
In some cases, the state helps television studios with the purchase of new filming equipment.
But viewers have to think about replacing the “receivers” themselves. All these difficulties do not allow us to suddenly switch to a new standard, no matter where such transformations are undertaken.
And in our country the transition was even more difficult. At first, a very high pace was taken, but after a few years, “the horses were changed in midstream”, saving time on the next evolutionary step: it was decided to introduce a more advanced second generation of the “terrestrial” standard - DVB-T2, which ensures the placement of a larger number of digital channels on the frequency analog channel bandwidth (compared to DVB-T).
It should be noted that the transition does not imply any increase in the resolution of the broadcast image. The project only involves changing the way it is presented, and we should expect HD quality on air only in the distant future (the standard supports HD, but at the state level it was decided not to touch this topic for now).
Today, DVB-T2 transmitters operate almost throughout the country. Somewhere, only 1 multiplex is currently included (a package that takes the place of one analog channel); in other areas the second one was already included. This means that, having the appropriate receiving equipment, you can watch 20 channels in decent quality from the air for free.
Although from the very beginning of the transition it was said that by 2015 our country should completely switch to digital and turn off analog, for now the issue of turning off was postponed, so analog television continues to function.
Photo: manufacturing companies
What is digital TV and television, how to choose the right one?
Before you decide to buy a digital TV or digital set-top box, it would be a good idea to understand what digital devices actually are. However, if you think a little, you will probably guess that any digital device, including TV, works based on digital signal processing. Currently, analog models in which exclusively analog signal processing took place are practically no longer produced, so they can be safely written off.
But we should not forget that digital channels on a TV do not occupy all the air space, and the analog signal is still broadcast. And even if you buy a digital TV model, this does not mean at all that it cannot cope with an analog signal. You can watch both.
How to choose a digital TV?
1. Read the theory carefully. On this point, just read my introductory paragraph. It is worth adding to this that digital models are necessarily equipped with special scalers - devices that are used to scale the broadcast image. Analogue models do not have scalers.
2. Think about what signal display technology you need: plasma or liquid crystals. In the first case, you will get improved quality, significant cost and high energy consumption. By sacrificing a little quality and purchasing a liquid crystal model, you can save a lot, both immediately and in the future.
3. The screen size of the TV you choose should depend on how acute your vision or the vision of all members of your family is. Believe me, looking at the little people on the screen every time is a pleasure. But too large objects at a distance of a meter are not comme il faut. Therefore, the diagonal of the screen should be three times smaller than the distance at which you will sit, stand or lie. Plus, remember that the larger the screen, the greater the energy consumption.
4. Consider when to connect additional devices to your digital TV. That is, if you want to connect a video player, camcorder, external drive, or mobile device to your purchase, make sure that the TV has the appropriate connectors.
5. Make sure that the device is capable of working with a DVB-T digital signal. Analogue television in our country only has a few years left to live, so this point needs to be thought through in advance. But if you have already bought a TV, and it is not able to process a digital signal, do not worry. You can always additionally purchase a digital set-top box that allows you to do this. You can easily find out how to set up a digital TV to work with such a set-top box from the instructions.
6. Consider adding a device to your purchase that allows you to watch YouTube videos. A very useful feature for owners of unlimited Internet access. However, some “smart” TVs can do this without additional gadgets. But they will cost much more.
What is digital television?
In conclusion, I would like to talk a little about digital television itself, which can be not only terrestrial, but also satellite and cable. Unlike the last two varieties, digital terrestrial television is free. So what is the difference between digital television and analogue television? The analog (electrical) signal is characterized by constant variability and transmission to the TV receiver from the translator. Directly on the TV it is processed and displayed in the form of visual and audio series.
As for the digital signal, before being sent from the translator, it is compressed and digitally encoded in the MPEG standard. This allows you to protect the signal from interference and loss of quality, as a result of which the picture on your screen will look almost perfect. That is, either you will see a 100% high-quality signal on TV, or you will not see it at all. There is no interference in the image.
Replacing an analog signal with a digital one in the future will make it possible to broadcast images in high-precision HD format, which analog devices are not capable of. According to forecasts, a complete transition to the digital standard will occur in 2015. By this time, more than twenty free channels will appear on the air, with the prospect of their constant increase. And even if you cannot receive a digital terrestrial signal, you can always appreciate its highest quality using cable or satellite television, which has been broadcasting excellent digital channels for a long time, including free ones.
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What is the difference between satellite television and cable, digital and analogue, and how to choose the type of broadcasting? Let’s try to understand the intricacies of this issue.
First, let's look at the types of broadcasting. There are only three of them:
- broadcasting. In this case, the channels are broadcast using television towers. To receive this type of broadcast, you must have an antenna to receive the signal.
- cable broadcasting. It is delivered to the consumer by companies - cable operators. In this case, the signal is transmitted via a cable, which must be installed by specialists in your apartment, if you contact them, of course.
— satellite broadcasting. Satellites distributed above the Earth's equator at an altitude of 36 thousand km broadcast channels. To receive signals from satellites, you need to acquire antennas - “dishes” aimed at them.
There are two types of terrestrial and cable television – analogue and digital. They differ in the way the signal is transmitted. An analog signal is significantly inferior in image and sound quality to a digital signal, which, by the way, also increases the number of broadcast channels. Due to its clear advantage, the latter is gaining more and more popularity. In the case of satellite television, digital has completely replaced analogue broadcasting.
In order to work with a digital signal, the TV model must be suitable. If this is not the case, you can use a receiver. This device converts the digital signal into another format that is understandable to the technology.
It is important to know that digital broadcast formats for broadcast, cable and satellite will be completely different. European standards look like this:
- DVB-T– broadcasting
- DVB-C— cable broadcasting
- DVB-S And DVB-S2— satellite broadcasting standards. The latter is more modern and promising.
What are the criteria for choosing a broadcast model?
Subscription fee. Today, this is provided for by cable and satellite TV; terrestrial TV will join them immediately after the transition from analogue to digital broadcasting. For satellite operators, the size of the subscription fee depends on the number of TV channels and their topics. This approach is gradually being introduced by cable television operators, and in the future it will most likely spread to the terrestrial model.
Necessary equipment. Each type of signal delivery requires certain technical equipment - an antenna for reception and a TV or TV tuner that supports the desired type of broadcasting. Prices for these devices vary - this point also needs to be taken into account when choosing.
Conditions of admission. In order for the signal to be transmitted without interference, it is necessary to take into account the characteristics of the type of broadcasting and the conditions for its reception. That is, if you watch TV in a country house far outside the city, then satellite TV will be the best option. If you live in the city on one of the top floors of a high-rise building, then you can safely choose broadcasting.
If your house, on the contrary, is low-rise, then the method of transmitting the signal via cables is suitable (if your house is connected to cable television).
Your preferences. For some, a few public channels are enough, while others want access to a wide variety of them. Each satellite and cable television operator has a different set of platforms offered, so you should focus on your interests.
There is an opinion that satellite television is of better quality than others, but such a statement is controversial. If the broadcast is digital, then, regardless of the method of signal transmission, the image can have very high clarity.
Signals are information codes that people use to convey messages in an information system. The signal can be given, but it is not necessary to receive it. Whereas a message can only be considered a signal (or a set of signals) that was received and decoded by the recipient (analog and digital signal).
One of the first methods of transmitting information without the participation of people or other living beings were signal fires. When danger arose, fires were lit sequentially from one post to another. Next, we will consider the method of transmitting information using electromagnetic signals and will dwell in detail on the topic analog and digital signal.
Any signal can be represented as a function that describes changes in its characteristics. This representation is convenient for studying radio engineering devices and systems. In addition to the signal in radio engineering, there is also noise, which is its alternative. Noise does not carry useful information and distorts the signal by interacting with it.
The concept itself makes it possible to abstract from specific physical quantities when considering phenomena related to the encoding and decoding of information. The mathematical model of the signal in research allows one to rely on the parameters of the time function.
Signal types
Signals based on the physical environment of the information carrier are divided into electrical, optical, acoustic and electromagnetic.
According to the setting method, the signal can be regular or irregular. A regular signal is represented as a deterministic function of time. An irregular signal in radio engineering is represented by a chaotic function of time and is analyzed using a probabilistic approach.
Signals, depending on the function that describes their parameters, can be analog or discrete. A discrete signal that has been quantized is called a digital signal.
Signal Processing
Analog and digital signals are processed and directed to transmit and receive information encoded in the signal. Once information is extracted, it can be used for various purposes. In special cases, information is formatted.
Analog signals are amplified, filtered, modulated, and demodulated. Digital data can also be subject to compression, detection, etc.
Analog signal
Our senses perceive all information entering them in analog form. For example, if we see a car passing by, we see its movement continuously. If our brain could receive information about its position once every 10 seconds, people would constantly get run over. But we can estimate distance much faster and this distance is clearly defined at each moment of time.
Absolutely the same thing happens with other information, we can evaluate the volume at any moment, feel the pressure our fingers exert on objects, etc. In other words, almost all information that can arise in nature is analogue. The easiest way to transmit such information is with analog signals, which are continuous and defined at any time.
To understand what an analog electrical signal looks like, you can imagine a graph that shows amplitude on the vertical axis and time on the horizontal axis. If we, for example, measure the change in temperature, then a continuous line will appear on the graph, displaying its value at each moment in time. To transmit such a signal using electric current, we need to compare the temperature value with the voltage value. So, for example, 35.342 degrees Celsius can be encoded as a voltage of 3.5342 V.
Analog signals used to be used in all types of communications. To avoid interference, such a signal must be amplified. The higher the noise level, that is, interference, the more the signal must be amplified so that it can be received without distortion. This method of signal processing spends a lot of energy generating heat. In this case, the amplified signal may itself cause interference for other communication channels.
Nowadays, analog signals are still used in television and radio, to convert the input signal in microphones. But in general, this type of signal is being replaced or replaced by digital signals everywhere.
Digital signal
A digital signal is represented by a sequence of digital values. The most commonly used signals today are binary digital signals, as they are used in binary electronics and are easier to encode.
Unlike the previous signal type, a digital signal has two values “1” and “0”. If we remember our example with temperature measurement, then the signal will be generated differently. If the voltage supplied by the analog signal corresponds to the value of the measured temperature, then a certain number of voltage pulses will be supplied in the digital signal for each temperature value. The voltage pulse itself will be equal to “1”, and the absence of voltage will be “0”. The receiving equipment will decode the pulses and restore the original data.
Having imagined what a digital signal will look like on a graph, we will see that the transition from zero to maximum is abrupt. It is this feature that allows the receiving equipment to “see” the signal more clearly. If any interference occurs, it is easier for the receiver to decode the signal than with analog transmission.
However, it is impossible to restore a digital signal with a very high noise level, while it is still possible to “extract” information from an analog type with large distortion. This is due to the cliff effect. The essence of the effect is that digital signals can be transmitted over certain distances, and then simply stop. This effect occurs everywhere and is solved by simply regenerating the signal. Where the signal breaks, you need to insert a repeater or reduce the length of the communication line. The repeater does not amplify the signal, but recognizes its original form and produces an exact copy of it and can be used in any way in the circuit. Such signal repetition methods are actively used in network technologies.
Among other things, analog and digital signals also differ in the ability to encode and encrypt information. This is one of the reasons for the transition of mobile communications to digital.
Analog and digital signal and digital-to-analog conversion
We need to talk a little more about how analog information is transmitted over digital communication channels. Let's use examples again. As already mentioned, sound is an analog signal.
What happens in mobile phones that transmit information via digital channels
Sound entering the microphone undergoes analog-to-digital conversion (ADC). This process consists of 3 steps. Individual signal values are taken at equal intervals of time, a process called sampling. According to Kotelnikov’s theorem on channel capacity, the frequency of taking these values should be twice as high as the highest signal frequency. That is, if our channel has a frequency limit of 4 kHz, then the sampling frequency will be 8 kHz. Next, all selected signal values are rounded or, in other words, quantized. The more levels created, the higher the accuracy of the reconstructed signal at the receiver. All values are then converted into binary code, which is transmitted to the base station and then reaches the other party, which is the receiver. A digital-to-analog conversion (DAC) procedure takes place in the receiver's phone. This is a reverse procedure, the goal of which is to obtain a signal at the output that is as identical as possible to the original one. Next, the analog signal comes out in the form of sound from the phone speaker.
Digital television is rapidly gaining popularity in our country, but many people still do not know how it fundamentally differs from the good old analog TV.
Description
It is not difficult to guess that analogue and digital television are based respectively. The analog signal is continuous, which means that in the event of any external influence it becomes vulnerable, which leads to worse picture and sound quality. An undoubted advantage of an analog signal is the ability to receive it using a simple terrestrial antenna. You can also use the services of a cable TV provider. We can say that the analog signal today is already outdated, since it is significantly inferior to the digital signal in a number of important parameters - quality, safety, etc.
Modern TVs are designed primarily to work with digital signals, although they also have an analog connector. The whole point is that an analog signal is not capable of revealing the full potential of modern plasma and LCD TVs; only a digital signal can provide better picture quality. Unlike analog, it arrives in compact “portions” that are separated by pauses, and therefore it is very difficult to influence such a signal. Even when transmitting a digital signal over a very long distance, the quality of picture and sound remains at the highest level. Among other things, a digital signal allows you to transmit much more channels than an analogue one, so subscribers who connect to digital television receive more than a hundred TV channels on a wide variety of topics.
Comparison
Alas, analogue television today actually has no obvious advantages over digital broadcasting, except perhaps the ability to “catch” a signal using a conventional antenna. However, digital television can also be mobile using a digital signal receiver. Considering that, regardless of the distance, the digital signal remains protected from hacking and interference and guarantees a high level of quality, the advantages of digital television become completely obvious.
Conclusions website
- Digital television provides a higher level of signal quality and protection. The analog signal was and remains vulnerable to external influences and cannot provide such high-quality images.
- Digital television is more mobile - today you can receive a digital signal while on the road or far from home.
- Analog television is not capable of providing as many channels as digital television. Due to the peculiarities of the digital signal, when connecting to digital TV, a subscriber can gain access to several hundred different TV channels.
