According to the signal transmission mode, it can be divided into three types: terrestrial wireless transmission (terrestrial digital TV DVB-T), satellite transmission (satellite digital TV DVB-S) and wired transmission (cable digital TV DVB-C).
According to product types, it can be divided into digital TV monitors, digital TV set-top boxes and integrated digital TV receivers.
Digital electronic chicken is one of the most talked about lively topics. As digital TV is a new thing, some specious concepts such as "digital TV", "all-digital TV", "all-media TV" and "multimedia TV" appear in some related reports and articles, which makes the public feel confused and at a loss. In fact, the meaning of "digital TV" does not refer to the TV set in our ordinary family, but refers to the TV system or TV equipment that uses digital signals in the process of processing, transmitting, transmitting and receiving TV signals. The specific transmission process is: the image and sound signals sent by TV stations are digitally compressed and modulated to form digital TV signals, which are transmitted by satellite, terrestrial broadcast or cable, and then received by digital TV, and the original images and sounds are restored through digital demodulation and digital video and audio decoding.
Analog signal refers to analog radio frequency signal, which is a modulated radio wave with a certain transmission frequency.
When the frequency of electromagnetic wave is lower than 100khz, the electromagnetic wave will be absorbed by the surface and cannot be effectively transmitted. However, when the frequency of electromagnetic waves is higher than 100khz, electromagnetic waves can propagate in the air and be reflected by the ionosphere at the outer edge of the atmosphere, forming a long-distance transmission capability. We call high-frequency electromagnetic waves with long-distance transmission capability RF.
What's the difference between RF signals and video signals?
They are completely different signals, the frequency of radio frequency is much higher, and they can transmit a variety of TV signals (including video and audio), so they are generally used for transmission. Video signal is an intermediate frequency signal, which generally only transmits one signal, and its quality is higher than that of radio frequency, but it is not suitable for long-distance transmission. Modulators and demodulators can be used to convert these two signals.
Radio frequency is the abbreviation of transmission frequency, which has a wide range. For example, the radio frequency of TV in China is 5-960Mhz, and the radio frequency of satellites is higher. Video is a transmission standard, with a bandwidth of 8Mhz, and is generally transmitted by wire.
Usually, a set of programs (8Mhz) is modulated to a certain frequency of RF, such as 57.25Mhz of CCTV and 208.25Mhz of Beijing Radio. In adjacent frequency transmission, a set of programs is modulated every 8MHZ, which has high frequency utilization rate.
Simply put, the TV antenna receives RF signals and the AV port receives video signals. The two cannot be mixed because the frequencies are different.
For example, JDATV-D1004 and JDATV-D 9812 are analog RF modulators.
Question: Is CATV a digital signal or an analog signal now? You can understand it this way.
Digital signals are binary numbers such as 010101kloc-0/0101transmitted by TV stations, which are restored to video scenes on your set-top box. The most important thing is that the transmitted image is not easily distorted.
Analog signals are video scenes transmitted by TV stations and displayed directly on your TV. The farther the transmission distance is, the more easily the image is distorted and the more blurred the TV you see.
I don't know if you understand this.
Question 3: What is analog TV? The cable TV we are watching now is analog TV, so we can add a set-top box. People who watch digital TV are called digital TV.
Question 4: What are the functions of digital TV and analog TV? Functions of digital TV: Using digital transmission technology, the transmission quality of signals can be improved without noise accumulation, the anti-interference ability of signals is greatly enhanced, and the viewing quality is high. Color * * * is true, there is no cross color, and there will be no accumulation of signal nonlinearity and phase distortion. It can receive different resolution levels (SD and HD) and is suitable for large screens and various displays. Mobile reception, no ghost. It can realize 5. 1 digital surround sound, and also has multilingual function. You can choose different languages when watching programs. Greatly improved the utilization rate of channel resources. Digital TV can enable analog forbidden channels (channels that can't be used due to the interference of the same channel and adjacent channels in the current cable TV spectrum allocation plan), and adopt digital audio and video compression technology to transmit 4 ~ 6 landmark clear digital TV programs or 1 channel high-definition TV programs in the existing analog channels of cable TV. It is easy to realize encryption/decryption and scrambling/descrambling processing, and it is convenient to carry out various conditional access charging services, thus conveniently realizing personalized service and characteristic service of TV in practice. Using digital technology can greatly improve the preservation quality and reproduction quality of TV programs, which can be copied countless times and preserved for a long time in theory. Using digital processing technology to produce all kinds of dazzling stunt forms, enhance the artistic effect and visual impact of the program, and greatly enhance the entertainment of the ambassador. Digital TV broadcasting has changed the way viewers watch TV programs, from passive reception to active quasi-interaction (local interaction) and interactive viewing. Due to the flexibility of digital technology, digital TV broadcasting can not only transmit radio and TV programs, but also provide various commercial services in other forms, such as data broadcasting, TV shopping, e-commerce, software download, video on demand, electronic program guide and so on. Analog TV: From the generation, transmission and processing of image signal to the recovery of receiver, the whole process is almost completed under the analog system. It is characterized by time axis sampling, vertical sampling in each frame and amplitude modulation transmission of TV image signals. In order to reduce the frequency band and avoid the sensitive frequency of human eyes to image reproduction, 1 frame image is divided into odd and even scanning fields. In addition, when the main technical parameters of analog TV were determined in 1960s and 1970s, the related theoretical and technical defects made the traditional analog TV have some shortcomings, such as easy interference, chromaticity distortion, bright color crosstalk, line crosstalk, line creep, large area flicker, low definition and weak telepresence. With the development of science and technology, especially digital technology, SARFT announced that analog TV will be closed in 20 15.
Question 5: What's the difference between analog TV and digital TV? Theoretically, digital signals can transmit high-definition programs. But the specific clarity depends on the clarity of TV front-end programs. At present, the definition standard adopted by domestic TV stations is the same as that of analog channels. Even some channels have been slightly reduced.
The clarity of analog signals also depends on the clarity of the front end of the TV station. However, compared with digital signals, analog signals have fewer processing links. Therefore, in the case of the same level, the effect of analog signal is better than that of digital signal. However, if the coding system is not used after all the digital signals are used in the future system, the digital signals are still slightly better than the analog signals.
In the final analysis, because the current digital signal is not a real digital signal, but just a compromise.
In addition, attenuation.
Attenuation is not an analog or digital difference, but an inherent characteristic of RF signals. According to different transmission media, RF signals will have different attenuation gains. The attenuation of optical fiber is relatively low, 1000m is about 0.2 dB, and that of coaxial cable is relatively high,1000 m is about 10dB. Moreover, the attenuation of high-frequency signals is greater than that of low-frequency signals.
Because digital signals and analog signals are the same, and both use radio frequency carriers, the attenuation equivalent of them is the same. There is no difference. The reason why digital signals look better is that the requirements of the receiving system for digital signals are relatively low, about 45 decibels, while the requirements for analog signals to enter the home are about 65 decibels. And there will be no snowflakes in the digital signal, which feels good. In fact, you can compare it.
Original post: zhidao.baidu/question/100542033
Question 6: What do you mean by analog signal? Television program signal data can be used to represent any information, such as symbols, characters, sounds, images, etc. , from the form of expression can be divided into two categories: analog signals and digital signals. The difference between analog signal and digital signal can be determined according to whether the amplitude value is discrete or not.
Analog signal means that the amplitude value is continuous (amplitude can be expressed by infinite value). Time-discrete analog signal is a kind of sampling signal, which is obtained by sampling the analog signal every t. Although its waveform is discontinuous in time, its amplitude is continuous, so it is still an analog signal, which is called pulse amplitude modulation (PAM) signal. Usually, the sound we hear and the TV images we see are analog signals.
The conversion from analog signal to digital signal generally goes through three processes: sampling, quantization and coding, and finally becomes a series of pulse digital signals represented by 0 and 1. Digital signals were first used in communication, which triggered a revolution in the field of communication.
1. Analog communication: The advantages of analog communication are intuitive and easy to realize, but it also has important disadvantages.
(1) has poor security.
Analog communication, especially microwave communication and wired communication, is easily eavesdropped. As long as the analog signal is received, it is easy to get the communication content.
(2) Weak anti-interference ability
In the process of electric signal transmission along the line, it will be interfered by various noises inside and outside the communication system, and it is difficult to separate the noise from the signal after mixing, thus reducing the communication quality. The longer the line, the more noise is accumulated.
Everyone has experience: every time you copy tapes and videos, the quality of sound and images is poor, which is why.
2. Digital communication system
Advantages of (1) digital transmission and exchange
① The confidentiality of communication is strengthened. After A/D conversion, the voice signal can be encrypted first, then transmitted, decrypted at the receiving end, and then restored to analog signal through D/A conversion.
② Anti-interference ability is improved. Digital signals will be mixed with noise during transmission. The input signal voltage can be measured by mosfet (called threshold) composed of electronic circuits. Only when the voltage reaches a certain amplitude, the circuit will have an output value and automatically generate neat pulses (called shaping or regeneration). When the small noise voltage comes, it will be filtered out because it is lower than the threshold value, and it will not cause circuit action. Therefore, the regenerated signal is exactly the same as the original signal, and only when the interference signal is greater than the original signal will an error code be generated. In order to prevent the error code, the method of error detection and correction is set in the circuit, that is, when the error code occurs, the opposite party can be retransmitted by using the reverse signal. Therefore, digital transmission is suitable for long-distance transmission and lines with poor performance.
③ A complete digital communication network can be built. After adopting time division switching, transmission and switching are unified, and a complete digital communication network can be formed.
(2) Disadvantages of digital communication
(1) occupies a wide frequency band. Because the line transmits pulse signals, it needs 20-64kHz bandwidth to transmit digital voice information, while an analog voice channel only occupies 4kHz bandwidth, that is, a PCM signal occupies several analog voice channels. For a certain telephone line, its utilization rate has decreased, or its requirements for the line have increased in detail.
② The technical requirements are complex, especially the synchronization technology requires high precision. If the receiver can correctly understand the meaning of the sender, it must correctly distinguish each symbol and find the beginning of each information group, which requires strict synchronization between the sender and the receiver. If a digital network is formed, it will be more difficult to solve the synchronization problem.
③ The analog-to-digital conversion will bring quantization error. With the use of large-scale integrated circuits and the popularization of broadband transmission media such as optical fiber, more and more digital signals are used for information storage and transmission, so analog signals must be converted from analog to digital, and quantization errors will inevitably occur in the conversion.
After the communication is converted from analog to digital, the benefits are well known: in the past, when the analog crossbar switch was used, the connection rate between a local office was less than 20%, and when the rural cable broadcasting was opened, the rural telephone could not be called, all of which were interference sounds ... After using the all-digital program-controlled switch and digital transmission circuit, the telephone connection rate was greatly improved, and the transmission quality was almost inaudible, forming a prefecture-level city as the area. A few years later, the digitalization of television was another revolution. ...& gt& gt
Question 7: What is the difference between digital signal and analog signal of TV signal? Ok, talk about the wrong concept of the first floor.
Theoretically, digital signals can transmit high-definition programs. But the specific clarity depends on the clarity of TV front-end programs. At present, the definition standard adopted by domestic TV stations is the same as that of analog channels. Even some channels have been slightly reduced.
The clarity of analog signals also depends on the clarity of the front end of the TV station. However, compared with digital signals, analog signals have fewer processing links. Therefore, in the case of the same level, the effect of analog signal is better than that of digital signal. However, if the coding system is not used after all the digital signals are used in the future system, the digital signals are still slightly better than the analog signals.
In the final analysis, because the current digital signal is not a real digital signal, but just a compromise.
In addition, attenuation.
Attenuation is not an analog or digital difference, but an inherent characteristic of RF signals. According to different transmission media, RF signals will have different attenuation gains. The attenuation of optical fiber is relatively low, 1000m is about 0.2 dB, and that of coaxial cable is relatively high,1000 m is about 10dB. Moreover, the attenuation of high-frequency signals is greater than that of low-frequency signals.
Because digital signals and analog signals are the same, and both use radio frequency carriers, the attenuation equivalent of them is the same. There is no difference. Ding thinks digital signals seem to be better, because the requirements of the receiving system for digital signals are relatively low, about 45 decibels, while the requirements for analog signals to enter the home are about 65 decibels. And there will be no snowflakes in the digital signal, which feels good. In fact, you can compare it.
Question 8: What's the difference between digital signals and analog signals? What are the advantages of watching TV with digital signals compared with analog signals? Signal data can be used to represent any information, such as symbols, characters, sounds, images and so on. , can be divided into analog signals and digital signals. The difference between analog signal and digital signal can be determined according to whether the amplitude value is discrete or not. Analog signal means that the amplitude value is continuous (amplitude can be expressed by infinite value). Time-discrete analog signal is a kind of sampling signal, which is obtained by sampling the analog signal every t. Although its waveform is discontinuous in time, its amplitude is continuous, so it is still an analog signal, which is called pulse amplitude modulation (PAM) signal. Usually, the sound we hear and the TV images we see are analog signals. The conversion from analog signal to digital signal generally goes through three processes: sampling, quantization and coding, and finally becomes a series of pulse digital signals represented by 0 and 1. Digital signals were first used in communication, which triggered a revolution in the field of communication. 1. Analog communication: The advantages of analog communication are intuitive and easy to realize, but it also has important disadvantages. (1) Analog communication with poor security, especially microwave communication and wired communication, is easy to be eavesdropped. As long as the analog signal is received, it is easy to get the communication content. (2) The electric signal with weak anti-interference ability will be interfered by various noises inside and outside the communication system during transmission along the line, and it is difficult to separate the noise from the signal after mixing, thus reducing the communication quality. The longer the line, the more noise is accumulated. Everyone has experience: every time you copy tapes and videos, the quality of sound and images is poor, which is why. 2. Advantages of digital communication (1) Digital transmission and exchange ① enhance the confidentiality of communication. After A/D conversion, the voice signal can be encrypted first, then transmitted, decrypted at the receiving end, and then restored to analog signal through D/A conversion. ② Anti-interference ability is improved. Digital signals will be mixed with noise during transmission. The input signal voltage can be measured by mosfet (called threshold) composed of electronic circuits. Only when the voltage reaches a certain amplitude, the circuit will have an output value and automatically generate neat pulses (called shaping or regeneration). When the small noise voltage comes, it will be filtered out because it is lower than the threshold value, and it will not cause circuit action. Therefore, the regenerated signal is exactly the same as the original signal, and only when the interference signal is greater than the original signal will an error code be generated. In order to prevent the error code, the method of error detection and correction is set in the circuit, that is, when the error code occurs, the opposite party can be retransmitted by using the reverse signal. Therefore, digital transmission is suitable for long-distance transmission and lines with poor performance. ③ A complete digital communication network can be built. After adopting time division switching, transmission and switching are unified, and a complete digital communication network can be formed. (2) Disadvantages of digital communication ① It occupies a wide frequency band. Because the line transmits pulse signals, it needs 20-64kHz bandwidth to transmit digital voice information, while an analog voice channel only occupies 4kHz bandwidth, that is, a PCM signal occupies several analog voice channels. For a certain telephone line, its utilization rate has decreased, or its requirements for the line have increased in detail. ② The technical requirements are complex, especially the synchronization technology requires high precision. If the receiver can correctly understand the meaning of the sender, it must correctly distinguish each symbol and find the beginning of each information group, which requires strict synchronization between the sender and the receiver. If a digital network is formed, it will be more difficult to solve the synchronization problem. ③ The analog-to-digital conversion will bring quantization error. With the use of large-scale integrated circuits and the popularization of broadband transmission media such as optical fiber, more and more digital signals are used for information storage and transmission, so analog signals must be converted from analog to digital, and quantization errors will inevitably occur in the conversion. After the communication is converted from analog to digital, the benefits are well known: in the past, when the analog crossbar switch was used, the connection rate between a local telephone office was less than 20%, and when the rural cable broadcasting was opened, the rural telephone could not be called, all of which were interference sounds ... After using the all-digital program-controlled switch and digital transmission circuit, the telephone connection rate was greatly improved, and the transmission quality was almost inaudible, forming a local area with prefecture-level cities as the unit. A few years later, the digitalization of television was another revolution.
Question 9: Regarding the analog and digital signals of TV, I think your set-top box is connected to the TV box first, and then to the LCD, but there is an interface converter (TV box) more than usual.
Firstly, check whether all interfaces are connected correctly, whether moving the thread head will cause image instability, and use it to detect whether the fault is related to the interface; Secondly, check the set-top box, preferably on TV, to see the effect. If it is normal on TV, the set-top box must be good. If you don't have a TV at home, borrow it from your neighbor's house. Then, it is judged that if the LCD is normal when used on the computer, it will generally not be a failure of the display; The intermediate link TV box, this is hard to say, there is the possibility of compatibility, but also the possibility of good or bad interface.
Watching TV with a digital TV set-top box will not switch between analog signals and digital signals, but what can cause automatic switching is that the TV is broken.
Troubleshooting is difficult because the TV box interface converter is connected. Your phenomenon is probably caused by compatibility problems between them, or transmission failure caused by interface problems. I suggest you use the above methods to check one by one, eliminate the impossible reasons, narrow down the cause of the failure, and then find a solution.
Question 10: What is the difference between digital TV and analog signal TV? Early picture tubes were all analog TVs-there was no digital signal from reception to playback.
There are many kinds of liquid crystal displays, such as receiving analog signals from antennas, but processing them with digital signals, and finally reaching the LCD screen. HDMI plug input, DVI input, mostly digital signals,
In the aspect of propagation, analog signals directly reflect the content of signals, and the demodulation is relatively simple, susceptible to interference and difficult to recover.
Digital signal, with only two levels of 0, 1, must go through a complicated demodulation process, but because it only has 0 and 1, it is easy to recover and save.
Digital processing is also very convenient,
As long as the digital signal is received, the signal is as clear as that sent, otherwise it can't be seen. Because the analog signal is weak, the noise will increase, the picture will be blurred and the noise will increase.
Analog TV, basically no delay, digital processing is time-consuming. There is usually a delay of several tenths to several seconds, which is more serious when you get off the satellite. Of course, users can't detect it without comparison, and the time display is different at most. . . . . .