Any signal, analog or digital, is electromagnetic oscillations that propagate at a certain frequency, depending on what signal is being transmitted, the device that receives this signal translates it into text, graphic or sound information that is convenient for the user or the device itself. For example, a television or radio signal, a tower or a radio station can transmit both analog and, at the moment, digital signal. The receiving device, receiving this signal, converts it into an image or sound, supplementing it with text information (modern radio receivers).

The sound is transmitted in analog form and already through the receiving device is converted into electromagnetic oscillations, and as already mentioned, the oscillations propagate with a certain frequency. The higher the sound frequency, the higher the vibration, which means the output sound will be louder. In general terms, an analog signal propagates continuously, a digital signal discontinuously (discretely).

Since the analog signal propagates constantly, the oscillations are summed up and a carrier frequency appears at the output, which in this case is the main one and the receiver is tuned to it. In the receiver itself, this frequency is separated from other vibrations, which are already converted into sound. The obvious disadvantages of transmission using an analog signal include a large amount of interference, low security of the transmitted signal, as well as a large amount of transmitted information, some of which is superfluous.

If we talk about a digital signal, where data is transmitted discretely, it is worth highlighting its obvious advantages:

• high level of protection of transmitted information due to its encryption;
• ease of digital signal reception;
• lack of extraneous "noise";
• digital broadcasting is capable of providing a huge number of channels;
• high quality of transmission - the digital signal provides filtering of the received data;

To convert an analog signal to digital and vice versa, special devices are used - an analog-to-digital converter (ADC) and a digital-to-analog converter (DAC). The ADC is installed in the transmitter, the DAC is installed in the receiver and converts the discrete signal into analog.

As far as security is concerned, why is digital signal more secure than analog. The digital signal is transmitted encrypted and the device that receives the signal must have a code to decode the signal. It is also worth noting that the ADC can also transmit the digital address of the receiver, if the signal is intercepted, then it will be impossible to completely decrypt it, since part of the code is missing - this approach is widely used in mobile communications.

To summarize, the main difference between analog and digital signal is the structure of the transmitted signal. Analog signals are a continuous stream of oscillations with varying amplitude and frequency. The digital signal is a discrete oscillation, the values ​​of which depend on the transmission medium.

Today we will try to figure out what are analog and digital signals? Their advantages and disadvantages. We will not throw various scientific terms and definitions, but try to figure out the situation on our fingers.

What is an analog signal?

An analog signal is based on the analogy of an electrical signal (current and voltage values) to the value of the original signal (pixel color, sound frequency and amplitude, etc.). Those. certain values ​​of current and voltage correspond to the transmission of a certain color of a pixel or an audio signal.

I will give an example on an analog video signal.

The voltage on the wire 5 volts corresponds to blue, 6 volts to green, 7 volts to red.

In order for red, blue and green stripes to appear on the screen, you need to alternately apply 5, 6, 7 volts to the cable. The faster we change the voltages, the thinner the stripes we get on the monitor. Reducing the interval between voltage changes to a minimum, we no longer get stripes, but alternating colored dots one after another.

An important feature of the analog signal is the fact that it is transmitted strictly from the transmitter to the receiver (for example, from the antenna to the TV), there is no feedback. Therefore, if interference interferes with the signal transmission (for example, instead of six volts, four will come), the color of the pixel will be distorted, and ripples will appear on the screen.
The analog signal is continuous.
What is digital signal?

Data transmission is also carried out using an electrical signal, but the values ​​of these signals are only two and they correspond to 0 and 1. That is, a sequence of zeros and ones is transmitted over the wires. Something like this: 01010001001, etc. In order for the receiving device (for example, a TV set) not to get confused in the transmitted data, the digits are transmitted in batches. It goes something like this: 10100010 10101010 10100000 10111110. Each such pack carries some information, for example, the color of a pixel. An important feature of a digital signal is that the transmitting and receiving devices can communicate with each other and correct errors one after another that may occur during transmission.

Examples of digital and analogue signal transmission

For a digital signal, transmission goes something like this:

• Interference: AAAAAAAAAAAAAA!
• TV: Which one? I can not hear!
• VCR: Green!
• TV: Yeah, got it! I draw green.
• TV: Please confirm that the color is red.
• VCR: I confirm.
• TV: Ok! I draw.

Transmission for analog signal:

• VCR: Hey, TV, the color of the pixel with coordinates 120x300 is green.
• Interference: AAAAAAAAAAAAAA!
• TV: Which one? I can not hear! Damn, I'll draw blue.
• VCR: The next color is red!
• Interference: BOOM! BOOM!
• TV: Red, sort of! I draw.
• VCR: Shovel!
• Interference: PShShShShSh!
• Television: ?!. Need to draw something ?! Let there be a shovel!

Advantages and disadvantages of digital and analog signals

From the above, we can conclude that, all other things being equal, the quality of information transmission using a digit will be higher than with an analog signal representation. At the same time, with good noise immunity, the two technologies can compete on equal terms.

When dealing with television and radio broadcasting, as well as modern types of communication, very often you have to come across terms such as "Analog signal" and "Digital signal"... For specialists in these words there is no mystery, but for people who are ignorant, the difference between "figure" and "analogue" may be completely unknown. And yet there is a very significant difference.

When we talk about a signal, we usually mean electromagnetic oscillations, which induce an EMF and cause fluctuations in the current in the receiver antenna. Based on these vibrations, the receiving device - TV, radio, walkie-talkie or cell phone - makes up an "idea" of what image to display on the screen (in the presence of a video signal) and what sounds to accompany this video signal.

In any case, the signal of a radio station or a mobile communication tower can appear in both digital and analog form. After all, for example, sound itself is an analog signal. At the radio station, the sound received by the microphone is converted into the already mentioned electromagnetic oscillations. The higher the sound frequency, the higher the output oscillation frequency, and the louder the speaker speaks, the greater the amplitude.

The resulting electromagnetic vibrations, or waves, propagate through space using a transmitting antenna. So that the air is 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 effect of sound are summed up, that is, "superimposed" on other vibrations that have a constant frequency. The last frequency is usually called "carrier", and it is to its perception that we tune our radio receiver in order to "catch" the analog signal of the radio station.

In the receiver, the opposite process takes place: the carrier frequency is separated, and the electromagnetic oscillations received by the antenna are converted into sound oscillations, and the familiar voice of the speaker is heard from the speaker.

Anything can happen in the process of transmitting an audio signal from the radio to the receiver. Third-party interference may occur, the frequency and amplitude may change, which, of course, will affect the sounds emitted by the radio receiver. Finally, both the transmitter and the receiver themselves introduce some error during signal conversion. Therefore, the sound reproduced by an analog radio receiver always has some distortion. The voice can be quite playable despite the changes, but the background will be hiss or even some wheezing caused by interference. The less confident 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 against unauthorized access. For public radio stations, this, of course, does not matter. But during the use of the first mobile phones, there was one unpleasant moment associated with the fact that almost any outside radio receiver could easily be tuned to the desired wavelength to eavesdrop on your telephone conversation.

Analog broadcasting has such disadvantages. Because of them, for example, television promises to become fully digital in a relatively short time.

Digital communications and broadcasting are considered to be more immune to interference and external influences. The point is that when using "digital" the analog signal from the microphone at the transmitting station is encrypted into a digital code. No, of course, the flow of numbers and numbers does not spread into the surrounding space. The sound of a certain frequency and volume is simply assigned a code from radio pulses. The duration and frequency of the pulses are predefined - it is the same for both the transmitter and the receiver. The presence of an impulse corresponds to one, the absence - to zero. Therefore, this connection is called "digital".

A device that converts an analog signal into a digital code is called analog-to-digital converter (ADC)... And the device installed in the receiver and converting the code into an analog signal corresponding to the voice of your friend in the speaker of a GSM cell phone is 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 ​​like 0.2 or 0.9 - just zero and one. Therefore, interference to digital communications and broadcasting has little effect.

Moreover, the "digit" is also more protected from unauthorized access. Indeed, in order for the DAC of the device to be able to decrypt the signal, it is necessary that it "knows" the decryption code. The ADC together with the signal can 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 a part of the code. This is especially true.

So here differences between digital and analog signals:

1) The analog signal can be distorted by interference, and the digital signal can be either clogged with interference at all, or arrive without distortion. The digital signal is either exactly there, or completely absent (or zero, or one).

2) The analog signal is available for perception by all devices operating on the same principle as the transmitter. The digital signal is reliably protected by a code, it is difficult to intercept it if it is not intended for you.

Analog, discrete and digital signals

INTRODUCTION TO DIGITAL SIGNAL PROCESSING

Digital signal processing (DSP or DSP - digital signal processing) is one of the newest and most powerful technologies, which is actively implemented in a wide range of fields of science and technology, such as communications, meteorology, radar and sonar, medical image imaging, digital audio and television broadcasting, exploration of oil and gas fields, etc. We can say that there is a widespread and deep penetration of digital signal processing technologies into all spheres of human activity. Today, DSP technology is one of the basic knowledge that scientists and engineers of all industries, without exception, need.

Signals

What is a signal? In the most general formulation, this is the dependence of one quantity on another. That is, from a mathematical point of view, a signal is a function. The most commonly considered time dependencies. The physical nature of the signal varies. Very often this is an electrical voltage, less often a current.

Signal presentation forms:

1. temporary;

2. spectral (in the frequency domain).

The cost of digital processing is less than analog and continues to decline, while the performance of computing operations continues to increase. It is also important that DSP systems are highly flexible. They can be supplemented with new programs and reprogrammed to perform various operations without changing the equipment. Therefore, interest in scientific and applied issues of digital signal processing is growing in all branches of science and technology.

FOREWORD TO DIGITAL SIGNAL PROCESSING

Discrete signals

The essence of digital processing is that physical signal(voltage, current, etc.) is converted into a sequence numbers, which is then subjected to mathematical transformations in VU.

Analog, discrete and digital signals

The original physical signal is a continuous function of time. Such signals, determined at all times t, are called analog.

What signal is called digital? Let's consider some analog signal (fig. 1.1 a). It is set continuously throughout the considered time interval. An analog signal is considered to be absolutely accurate if measurement uncertainty is not taken into account.

Rice. 1.1 a) Analog signal

Rice. 1.1 b) Sampled signal

Rice. 1.1 c) Quantized signal

To receive you need to digital signal, you need to carry out two operations - sampling and quantization... The process of converting an analog signal into a sequence of samples is called sampling, and the result of such a transformation is discrete signal.T. arr., sampling consists in compiling a sample from an analog signal (Fig.1.1 b), each element of which, called countdown, will be spaced in time from neighboring samples at a certain interval T called sampling interval or (since the sampling interval is more often the same) - sampling period... The reciprocal of the sampling period is called sampling rate and is defined as:

(1.1)

When processing a signal in a computing device, its samples are represented as binary numbers with a limited number of bits. As a result, samples can take only a finite set of values ​​and, therefore, when a signal is presented, its rounding inevitably occurs. The process of converting signal samples into numbers is called quantization... The resulting round-off errors are called rounding errors or quantization noise... Thus, quantization is the reduction of the levels of the sampled signal to a certain grid (Fig. 1.1 c), more often by the usual rounding towards a larger one. Time discrete and level-quantized signal will be digital.

The conditions under which it is possible to completely restore an analog signal from its digital equivalent while preserving all the information originally contained in the signal are expressed by the theorems of Nyquist, Kotelnikov, Shannon, the essence of which is practically the same. For sampling an analog signal with complete preservation of information in its digital equivalent, the maximum frequencies in the analog signal must be at least half the sampling frequency, that is, f max £ (1/2) f d, i.e. at one period of the maximum frequency there must be at least two samples. If this condition is violated, the effect of masking (substitution) of the actual frequencies with lower frequencies occurs in the digital signal. In this case, instead of the actual one, the "apparent" frequency is recorded in the digital signal, and, therefore, the restoration of the actual frequency in the analog signal becomes impossible. The reconstructed signal will look as if the frequencies above half of the sampling rate reflected from the frequency (1/2) f d into the lower part of the spectrum and superimposed on the frequencies already present in this part of the spectrum. This effect is called aliasing or aliasing(aliasing). An illustrative example of aliasing is an illusion that is quite common in the cinema - a car wheel begins to rotate against its movement if the wheel makes more than half a revolution between successive frames (analogous to the sampling rate).

Signal to digital conversion performed by analog-to-digital converters (ADC). As a rule, they use a binary number system with a certain number of digits on a uniform scale. An increase in the number of digits increases the measurement accuracy and expands the dynamic range of the measured signals. The information lost due to the lack of ADC bits is unrecoverable, and there are only estimates of the arising error of "rounding" of the samples, for example, through the noise power generated by the error in the last ADC bit. For this, the concept of signal-to-noise ratio is used - the ratio of signal power to noise power (in decibels). The most commonly used are 8-, 10-, 12-, 16-, 20-, and 24-bit ADCs. Each additional digit improves the signal-to-noise ratio by 6 decibels. However, increasing the number of bits decreases the sampling rate and increases the hardware cost. An important aspect is also the dynamic range, which is determined by the maximum and minimum signal values.

Digital signal processing is performed either by special processors, or on general-purpose computers and computers using special programs. Most easy to consider linear systems. Linear are called systems for which the principle of superposition takes place (the response to the sum of input signals is equal to the sum of responses to each signal separately) and homogeneity (a change in the amplitude of the input signal causes a proportional change in the output signal).

If the input signal x (t-t 0) generates an unambiguous output signal y (t-t 0) for any shift t 0, then the system is called time invariant... Its properties can be investigated at any arbitrary moments in time. To describe the linear system, a special input signal is introduced - single impulse(impulse function).

Single impulse(single count) u 0(n) (Fig. 1.2):

Rice. 1.2. Single impulse

Due to the properties of superposition and homogeneity, any input signal can be represented as the sum of such pulses supplied at different times and multiplied by the corresponding coefficients. The system output signal in this case is the sum of the responses to these pulses. The response to a single impulse (impulse with a unit amplitude) is called impulse response systemh (n). Knowing the impulse response allows you to analyze the passage of any signal through a discrete system. Indeed, an arbitrary signal (x (n)) can be represented as a linear combination of unit samples.

The difference between analog and digital communication.
When dealing with radio communication, very often you have to come across terms such as "Analog signal" and "Digital signal"... For specialists in these words there is no mystery, but for people who are ignorant, the difference between "figure" and "analogue" may be completely unknown. And yet there is a very significant difference.
So. Radio communication is always the transmission of information (voice, SMS, telesignalization) 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, which induce an EMF and cause fluctuations in the current in the receiver antenna. Further, 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 the radio station, the sound received by the microphone is converted into the already mentioned electromagnetic oscillations. The higher the sound frequency, the higher the output oscillation frequency, and the louder the speaker speaks, the greater the amplitude.
The resulting electromagnetic vibrations, or waves, propagate through space using a transmitting antenna. So that the air is 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 effect of sound are summed up, that is, "superimposed" on other vibrations that have a constant frequency. The last frequency is usually called "carrier", and it is to its perception that we tune our radio receiver in order to "catch" the analog signal of the radio station.
The reverse process takes place 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 who transmitted the message wanted to convey is heard from the speaker.
In the process of transmitting the 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 emitted by the radio receiver. Finally, both the transmitter and the receiver themselves introduce some error during signal conversion. Therefore, the sound reproduced by an analog radio receiver always has some distortion. The voice can be quite playable despite the changes, but the background will be hiss or even some wheezing caused by interference. The less confident 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 against unauthorized access. For public radio stations, this, of course, does not matter. But during the use of the first mobile phones, there was one unpleasant moment associated with the fact that almost any outside radio receiver could easily be tuned to the desired wavelength to eavesdrop on your telephone conversation.

To protect against this, the so-called "toning" of the signal or, in other words, the CTCSS (Continuous Tone-Coded Squelch System) system, a continuous tone coded noise reduction system or a "friend / foe" signal identification system, designed to separate users operating in the same frequency range, is used. into groups. Users (correspondents) from the same group can hear each other thanks to the identification code. Explaining in an accessible manner, the principle of operation of this system is as follows. Together with the transmitted information, an additional signal (or in another tone) is also sent on the air. The receiver, in addition to the carrier, recognizes this tone with the appropriate setting and receives the signal. If the tone is not tuned in the radio-receiver, then the signal is not received. There are quite a lot of encryption standards that differ for different manufacturers.
Analog broadcasting has such disadvantages. Because of them, for example, television promises to become fully digital in a relatively short time.

Digital communications and broadcasting are considered to be more immune to interference and external influences. The point is that when using "digital" the analog signal from the microphone at the transmitting station is encrypted into a digital code. No, of course, the flow of numbers and numbers does not spread into the surrounding space. The sound of a certain frequency and volume is simply assigned a code from radio pulses. The duration and frequency of the pulses are predefined - it is the same for both the transmitter and the receiver. The presence of an impulse corresponds to one, the absence - to zero. Therefore, this connection is called "digital".
A device that converts an analog signal into a digital code is called analog-to-digital converter (ADC)... A device installed in the receiver and converting 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 ​​like 0.2 or 0.9 - just zero and one. Therefore, interference to digital communications and broadcasting has little effect.
Moreover, the "digit" is also more protected from unauthorized access. Indeed, in order for the DAC of the device to be able to decrypt the signal, it is necessary that it "knows" the decryption code. The ADC together with the signal can 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 a part of the code. This is especially true for communication.
So, differences between digital and analog signals:
1) The analog signal can be distorted by interference, and the digital signal can be either clogged with interference at all, or arrive without distortion. The digital signal is either exactly there, or completely absent (or zero, or one).
2) The analog signal is available for perception by all devices operating on the same principle as the transmitter. The digital signal is reliably protected by a code, it is difficult to intercept it if it is not intended for you.

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

But time passes, and the station ceases to suit you as a user. Yes, it is reliable, but powerful, and with a good battery up to 2600 mAh. But when the park of radio stations is expanded by more than 100 people, and especially when working in groups, its 16 channels begin to be lacking.
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 maintaining the existing communication system in working order.

The advantages of this transition are undeniable.
You get the station up and running
1) longer (there is less consumption in digital mode.)
2) More functions (group call, lone worker)
3) 32 memory channels.
That is, you actually create initially 2 channel bases. 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 number of radio stations of the second bank and increase the number of the first.
Ultimately, you will achieve the set task - to transfer your entire base to a digital communication standard.
Yaesu Fusion DR-1 digital repeater can serve as a good addition and extension to any base.

It is a dual-band (144 / 430MHz) repeater that supports analog FM communication as well as digital protocol at the same time System fusion within the frequency range of 12.5 kHz. We are confident that the implementation of the latest DR-1X will be the dawn of our new and impressive multifunctional system System Fusion.
One of the key features System fusion is the function AMS (automatic mode selection) which instantly recognizes whether a signal is received in V / D mode, voice mode or FR data mode by analog FM or digital C4FM, and automatically switches to the corresponding one. Thus, thanks to our digital transceivers FT1DR and FTM-400DRSystem fusion to keep in touch with analog FM radio stations, you no longer need to manually switch modes each time.
On repeater DR-1X, AMS can be configured to convert the incoming digital C4FM signal to analog FM and retransmit it, thus allowing communication between digital and analog transceivers. AMS it can also be configured to automatically relay the incoming mode to the output, allowing digital and analog users to share the same repeater.
Until now, FM repeaters have only been used for traditional FM communications, and digital repeaters have been used for digital only. However, now simply replacing the conventional analog FM repeater with DR-1X, you can continue to use regular FM communications, as well as use a repeater for more advanced digital radio communications System fusion ... Other peripherals such as duplexer and amplifier, etc. can continue to be used as usual.

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