Analog and digital signal. Types of signals and how they work. Digital and analogue television: what is the difference and which is better

Difference between analog and digital communications.
When dealing with radio communications, you often come across terms such as "analog signal" And "digital signal". For specialists there is no mystery in these words, but for ignorant people the difference between “digital” and “analogue” may be completely unknown. Meanwhile, there is a very significant difference.
So. Radio communication is always the transmission of information (voice, SMS, telesignaling) between two subscribers - a signal source - a transmitter (Radio station, repeater, base station) and a receiver.
When we talk about a signal, we usually mean electromagnetic oscillations that induce EMF and cause current fluctuations in the receiver antenna. Next, the receiving device converts the received vibrations back into an audio frequency signal and outputs it to the speaker.
In any case, the transmitter signal can be represented in both digital and analog form. After all, for example, sound itself is an analog signal. At a radio station, the sound received by the microphone is converted into the already mentioned electromagnetic waves. The higher the sound frequency, the higher the output oscillation frequency, and the louder the speaker speaks, the greater the amplitude.
The resulting electromagnetic oscillations, or waves, are propagated in space using a transmitting antenna. So that the airwaves are not clogged with low-frequency interference, and so that different radio stations have the opportunity to work in parallel without interfering with each other, the vibrations resulting from the influence of sound are summed up, that is, “superimposed” on other vibrations that have a constant frequency. The last frequency is usually called the “carrier”, and it is to perceive it that we tune our radio receiver in order to “catch” the analog signal of the radio station.
The reverse process occurs in the receiver: the carrier frequency is separated, and the electromagnetic oscillations received by the antenna are converted into sound oscillations, and the information that the person sending the message wanted to convey is heard from the speaker.
During the transmission of an audio signal from the radio station to the receiver, third-party interference may occur, the frequency and amplitude may change, which, of course, will affect the sounds produced by the radio receiver. Finally, both the transmitter and receiver themselves introduce some error during signal conversion. Therefore, the sound reproduced by an analog radio always has some distortion. The voice may be fully reproduced, despite the changes, but there will be hissing or even some wheezing in the background caused by interference. The less reliable the reception, the louder and more distinct these extraneous noise effects will be.

In addition, the terrestrial analog signal has a very weak degree of protection from unauthorized access. For public radio stations this, of course, makes no difference. But when using the first mobile phones, there was one unpleasant moment associated with the fact that almost any third-party radio receiver could easily be tuned to the desired wavelength to eavesdrop on your telephone conversation.

To protect against this, they use the so-called “toning” of the signal or, in other words, the CTCSS system (Continuous Tone-Coded Squelch System), a noise reduction system coded with a continuous tone, or a “friend/foe” signal identification system, designed to separate users working in the same frequency range, into groups. Users (correspondents) from the same group can hear each other thanks to an identification code. Explaining clearly, the operating principle of this system is as follows. Along with the transmitted information, an additional signal (or another tone) is also sent over the air. The receiver, in addition to the carrier, recognizes this tone with appropriate settings and receives the signal. If the tone is not set in the radio-receiver, then the signal is not received. There are a fairly large number of encryption standards that differ for different manufacturers.
Analogue broadcasting has such disadvantages. Because of them, for example, television promises to become completely digital in a relatively short time.

Digital communications and broadcasting are considered more protected from interference and external influences. The thing is that when using “digital”, the analog signal from the microphone at the transmitting station is encrypted into a digital code. No, of course, a stream of figures and numbers does not spread into the surrounding space. Simply, a code of radio pulses is assigned to a sound of a certain frequency and volume. The duration and frequency of the pulses are predetermined - it is the same for both the transmitter and the receiver. The presence of an impulse corresponds to one, the absence - zero. Therefore, such communication is called “digital”.
A device that converts an analog signal into a digital code is called analog-to-digital converter (ADC). And a device installed in the receiver that converts the code into an analog signal corresponding to the voice of your friend in the speaker of a GSM cell phone, called a digital-to-analog converter (DAC).
During digital signal transmission, errors and distortions are virtually eliminated. If the impulse becomes a little stronger, longer, or vice versa, then it will still be recognized by the system as a unit. And zero will remain zero, even if some random weak signal appears in its place. For ADC and DAC, there are no other values ​​such as 0.2 or 0.9 - only zero and one. Therefore, interference has almost no effect on digital communications and broadcasting.
Moreover, “digital” is also more protected from unauthorized access. After all, in order for the device’s DAC to decrypt the signal, it must “know” the decryption code. The ADC, along with the signal, can also transmit the digital address of the device selected as the receiver. Thus, even if the radio signal is intercepted, it cannot be recognized due to the absence of at least part of the code. This is especially true for communications.
So, differences between digital and analog signals:
1) An analog signal can be distorted by interference, and a digital signal can either be completely clogged with interference, or arrive without distortion. The digital signal is either definitely present or completely absent (either zero or one).
2) The analog signal is accessible to all devices operating on the same principle as the transmitter. The digital signal is securely protected by a code and is difficult to intercept if it is not intended for you.

In addition to purely analogue and purely digital stations, there are also radio stations that support both analogue and digital modes. They are designed for the transition from analogue to digital communications.
So, having a fleet of analogue radio stations at your disposal, you can gradually switch to a digital communication standard.
For example, initially you built a communication system at Radio Stations Baikal 30.
Let me remind you that this is an analog station with 16 channels.

But time passes, and the station ceases to suit you as a user. Yes, it is reliable, yes, powerful, and with a good battery up to 2600 mAh. But when expanding the fleet of radio stations by more than 100 people, and especially when working in groups, its 16 channels begin to be insufficient.
You don’t have to immediately run out and buy digital radio stations. Most manufacturers deliberately introduce a model with an analog transmission mode.
That is, you can gradually switch to, for example, Baikal -501 or Vertex-EVX531 while keeping the existing communication system in working order.

The advantages of such a transition are undeniable.
You get a working station
1) longer (in digital mode there is less consumption.)
2) Having more functions (group call, lone worker)
3) 32 memory channels.
That is, you actually create initially 2 channel databases. For new purchased stations (digital channels) and a base of assistance channels with existing stations (analogue channels). Gradually, as you purchase equipment, you will reduce the fleet of radio stations of the second bank and increase the fleet of the first.
Ultimately, you will achieve your goal - to transfer your entire base to a digital communication standard.
A good addition and expansion to any base can be the Yaesu Fusion DR-1 digital repeater

This is a dual-band (144/430MHz) repeater that supports analog FM communication, as well as a digital protocol at the same time System Fusion within the frequency range of 12.5 kHz. We are confident that the introduction of the latest DR-1X will be the dawn of our new and impressive multi-functional system System Fusion.
One of the key features System Fusion is a function AMS (Automatic Mode Select), which instantly recognizes whether a signal is being received in V/D mode, voice mode or data mode FR analog FM or digital C4FM, and automatically switches to the appropriate one. Thus, thanks to our digital transceivers FT1DR And FTM-400DRSystem Fusion To maintain communication with analog FM radio stations, there is no longer a need to manually switch modes each time.
On repeater DR-1X, AMS can be configured so that the incoming digital C4FM signal is converted to analog FM and rebroadcast, thus allowing communication between digital and analog transceivers. AMS can also be configured to automatically relay incoming mode to output, allowing digital and analogue users to share a single repeater.
Until now, FM repeaters were used only for traditional FM communications, and digital repeaters only for digital communications. However, now simply by replacing the conventional analog FM repeater with DR-1X, you can continue to use regular FM communications, but also use a repeater for more advanced digital radio communications System Fusion . Other peripherals such as duplexer and amplifier, etc. you can continue to use it as usual.

More detailed characteristics of the equipment can be seen on the website in the products section

Any signal, whether analog or digital, is an electromagnetic oscillation that propagates at a certain frequency. Depending on what signal is being distributed, the device receiving this signal determines what image to display on the screen, respectively, with sound.

For example, a television tower or radio station can transmit both analog and digital signals. Sound is transmitted in analog form, and through the receiving device is converted into electromagnetic vibrations. As already mentioned, vibrations propagate with a certain frequency. The higher the frequency of the sound, the higher the vibrations, resulting in a louder sounding voice.

In general terms, an analog signal propagates continuously, and a digital signal propagates discretely (intermittently), i.e. the amplitude of oscillations takes on certain values ​​per unit time.

If we continue the example of an analog audio signal, we get a process in which electromagnetic waves are propagated using a transmitter (antenna). Because The analog signal propagates constantly, then the oscillations are summed up, and a carrier frequency appears at the output, which is the fundamental one, i.e. The receiver is tuned to it.

In the receiver itself, this frequency is separated from other vibrations, which are converted into sound.

The disadvantages of transmitting information using an analog signal are obvious:

• There is a lot of interference;
• More unnecessary information is transmitted;
• Signal Transmission Security

If in radio broadcasting the transmission of information using an analog signal occurs less noticeably, then in television, the issue of switching to digital transmission is extremely important.

The main advantages of a digital signal over an analog signal are:

• Higher level of protection. The security of digital signal transmission is based on the fact that the “digit” is transmitted in encrypted form;
• Ease of signal reception. A digital signal can be received at any distance from your place of residence;
• Digital broadcasting can provide a huge number of channels. It is this opportunity that provides fans of digital television with a large number of TV channels for watching films and programs;
• The transmission quality is several orders of magnitude higher than with analogue broadcasting. The digital signal provides filtering of received data, and it is also possible to restore the original information.

Accordingly, special devices are used to convert an analog signal into a digital one, and vice versa.

• A device that converts an analog signal to a digital signal is called an analog-to-digital converter (ADC);
• A device that converts a digital signal into an analog signal is called a digital-to-analog converter (DAC).

Accordingly, the ADC is installed in the transmitter, and the DAC is installed in the receiver and converts the discrete signal into an analogue signal corresponding to the voice.

Why is a digital signal more secure?

The digital signal is transmitted in encrypted form and the digital-analog device must have a code for decryption. The ADC can also transmit the digital address of the receiver. Even if the signal is intercepted, it will be impossible to completely decipher it due to the absence of part of the code. This property of digital transmission is widely used in mobile communications.

Thus, the main difference between an analog and digital signal is the different structure of the transmitted signal. Analog signals are a continuous stream of oscillations with varying amplitude and frequency.

A digital signal is discrete (intermittent) oscillations, the values ​​of which depend on the transmitting medium.

Sometimes consumers have questions about how the signal is transmitted on television.

In television, before transmitting a signal in digital form, the analog signal must be digitized. After this, you need to choose the medium in which the transmission will take place: copper cable, airwaves, fiber optic cable.

For example, many users are sure that cable television is only digital data transmission. This is wrong. Cable television is both an analogue and digital type of signal transmission.

A person talks on the phone every day, watches various TV channels, listens to music, and surfs the Internet. All communications and other information environments are based on the transmission of signals of various types. Many people ask questions about how analog information differs from other types of data, what a digital signal is. The answer to them can be obtained by understanding the definition of various electrical signals and studying their fundamental differences between each other.

Analog signal

An analog signal (continuous) is a natural information signal that has a certain number of parameters that are described by a time function and a continuous set of all possible values.

Human senses capture all information from the environment in analog form. For example, if a person sees a truck passing nearby, then its movement is observed and changes continuously. If the brain received information about the movement of vehicles once every 15 seconds, then people would always fall under its wheels. A person evaluates distance instantly, and at each moment in time it is defined and different.

The same thing happens with other information - people hear sound and evaluate its volume, evaluate the quality of the video signal, and the like. Accordingly, all types of data are analog in nature and are constantly changing.

On a note. Analog and digital signals are involved in transmitting the speech of interlocutors who communicate by telephone; the Internet operates on the basis of the exchange of these signal channels over a network cable. These types of signals are electrical in nature.

An analog signal is described by a mathematical time function similar to a sine wave. If you take measurements, for example, of water temperature, periodically heating and cooling it, then the graph of the function will display a continuous line that reflects its value in each time period.

To avoid interference, such signals must be amplified using special means and devices. If the level of signal interference is high, then it needs to be amplified more. This process is accompanied by large expenditures of energy. An amplified radio signal, for example, can often itself become an interference for other communication channels.

Interesting to know. Analog signals were previously used in all types of communications. However, now it is being replaced everywhere or has already been replaced (mobile communications and the Internet) by more advanced digital signals.

Analog and digital television still coexist, but the digital type of television and radio broadcasting is rapidly replacing the analog method of data transmission due to its significant advantages.

To describe this type of information signal, three main parameters are used:

• frequency;
• wave length;
• amplitude.

Disadvantages of an analog signal

An analog signal has the following properties, which show their difference from the digital version:

1. This type of signal is characterized by redundancy. That is, the analog information in them is not filtered - they carry a lot of unnecessary information data. However, it is possible to pass information through a filter, knowing additional parameters and the nature of the signal, for example, using the frequency method;
2. Safety. He is almost completely helpless against unauthorized intrusions from the outside;
3. Absolute helplessness in the face of various types of interference. If any interference is imposed on the data transmission channel, it will be transmitted unchanged by the signal receiver;
4. There is no specific differentiation of sampling levels - the quality and quantity of transmitted information is not limited in any way.

The above properties are disadvantages of the analog method of data transmission, on the basis of which it can be considered completely obsolete.

Digital and discrete signals

Digital signals are artificial information signals, presented in the form of regular digital values ​​that describe specific parameters of the transmitted information.

For information. Nowadays, a simple-to-encode bit stream is predominantly used - a binary digital signal. This is the type that can be used in binary electronics.

The difference between the digital type of data transmission and the analog version is that such a signal has a specific number of values. In the case of a bit stream, there are two of them: “0” and “1”.

The transition from zero to maximum in a digital signal is abrupt, allowing the receiving equipment to read it more clearly. If certain noise and interference occurs, it will be easier for the receiver to decode a digital electrical signal than with analog information transmission.

However, digital signals differ from the analog version in one drawback: with a high level of interference, they cannot be restored, but it is possible to extract information from a continuum signal. An example of this would be a telephone conversation between two people, during which entire words and even phrases of one of the interlocutors may disappear.

This effect in the digital environment is called the break effect, which can be localized by reducing the length of the communication line or installing a repeater, which completely copies the original type of signal and transmits it further.

Analog information can be transmitted over digital channels after going through the digitization process with special devices. This process is called analog-to-digital conversion (ADC). This process can also be reversed - digital-to-analog conversion (DAC). An example of a DAC device would be a digital TV receiver.

Digital systems are also distinguished by the ability to encrypt and encode data, which has become an important reason for the digitization of mobile communications and the Internet.

Discrete signal

There is a third type of information – discrete. A signal of this kind is intermittent and changes over time, taking on any of the possible (prescribed in advance) values.

Discrete information transfer is characterized by the fact that changes occur according to three scenarios:

1. The electrical signal changes only in time, remaining continuous (unchanged) in magnitude;
2. It changes only in magnitude, while remaining continuous in time;
3. It can also change simultaneously in both magnitude and time.

Discreteness has found application in batch transmission of large amounts of data in computing systems.

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.

With the development of digital technologies, there is gradually a smooth migration of television viewers from analogue to digital television.

This happens not only because of large-scale advertising campaigns launched by Internet providers to popularize and sell IPTV, but also because users certainly like such television.

Why? Let's figure it out.

Differences between digital TV and analogue

I won’t spoil things here about digital and analog signals, who cares? No one. Let's take a closer look at the practical difference in use.

Equipment

So, to watch analog television you need a regular terrestrial antenna (in an apartment, on the roof) or a cable television connected to some company. Due to the specifics of how an analog signal works (after all, I had to write about signals), the image can be distorted in every possible way under the influence of external sources of interference.

In turn, to watch digital television, a regular antenna is not enough. You will have to install a receiver (encrypted digital signal decoder) near the TV, which will convert the received data into an image and display the picture on the TV screen.

A good example is Interactive TV from Rostelecom, which I wrote about in great detail in the article.

Digital satellite TV is a little different from the previous example. And if you want to watch satellite television, you will have to install a satellite dish (“dish”) on the wall of your private or apartment building. This time, the Tricolor TV company can be cited as an example.

Naturally, the satellite TV provider will provide you with all the necessary equipment and install an antenna. But the number of channels will depend on the selected service package.

Image quality

Without a doubt, digital television is the leader in this regard in all respects. Here are some obvious advantages of digital:

• Does not lose signal quality if transmitted over very long distances;
• The image cannot contain glare, “snow”, picture distortion and other common defects when watching analog television;
• Possibility of connecting channels in HD quality. One could safely put this item first on the list, since a high-definition image is the dream of any TV viewer who has a large diagonal TV screen.

Other options

Undoubtedly, in addition to image quality, IPTV has many other advantages:

Somehow I’ve gotten really into trouble with my writing, it’s time to finish.

Digital TV is better and higher quality than analogue

Summarizing all of the above, we can conclude that analog television has practically become obsolete, since it is inferior to digital television in almost everything except cost (“analogue” can be watched for free).

Some of the readers may have thought: “I’ll buy a TV with a built-in TV tuner, set it up to receive satellite TV and watch digital for free.” No, my dears, it’s not that simple. Firstly, there will be free (unencrypted) channels “one, two and gone,” and secondly, you still need to be able to find the right satellite and configure the equipment.

In general, Russia will not have a complete transition to digital TV for a very long time. 10-20 years, or even more. Although, many countries are striving for this, including our great Motherland. In the meantime, there is only one way out - to buy good digital television from Internet providers and highly specialized companies.

That's all, thanks for your attention.

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