I. Differential phase: Differential phase refers to the phase change of the color carrier component caused by the magnitude of brightness signals related to chromaticity. In the NTSC system, the change in color signal vector angle represents the change in hue, so the differential phase on the signal is very serious. By the PAL system uses progressive inverting techniques, it is self-compensating to replace the change in hue with a change in color saturation. In general, the differential phase is a parameter used to describe the amplitude change of the brightness signal on the color tone effect. Second, differential gain: Differential gain is a functional relationship between the amplitude of the color signal with a function of luminance signal amplitude changes, and its impact on the image is a change in color saturation. Simply put: Differential gain is the impact of changes in brightness signal amplitude on color saturation. Third, color-bright shattered: color-bright schurn is the reaction of the differential gain, which indicates the relationship between the brightness signal with the change of the chromatic sub-waveness. Fourth, R (马) Correction: The so-called horses correction is to detect the dark part and light colored parts in the image signal, and increase the proportion of the two to improve the image contrast effect. V. Sound surface wave filter (SAWF) sound surface wave filter is made of quartz, lithium niobate, and barium titanate crystals have the properties of the piezoelectric effect. The so-called piezoelectric effect is that when the crystal is mechanically active, the phenomenon of the electric field proportional to the pressure is generated. A crystal having a piezoelectric effect, and the elastic deformation is generated when the electrical signal is active, and the electrical signal can be converted to the acoustic signal. Since this acoustic wave is only propagated on the surface of the crystal, it is called a sound surface wave. The English abbreviation of the sound surface Wave filter is SAWF, which has a small size, light weight, reliable performance, and does not require complex adjustment. Realize key devices of neighbor frequency transmission in cable television systems. The visual surface wave filter is: (1) frequency response flat, unevenness is only ± 0.3- ± 0.5dB, and the group is delayed ± 30- ± 50ns. (2) The SAWF rectangular coefficient is good, and the external suppression can reach 40 dB. (3) The insertion loss is up to 25-30 dB, but the magnitude can be compensated for loss. The sound surface wave filter includes an acoustic surface wave television image intermediate frequency filter, a television audio filter, a television channel residual edge filter. The typical technical indicators of the sound surface wave filter are shown in the table below. Sixth, comb filter comb filter It is a passband and blockbus arranged in the same frequency interval, allowing only some specific frequency range signals. The comb filter has a characteristic curve inexplica, so it is called a comb filter. There are many applications in comb filter in television technology. The comb filter is used to separate two orthogonal components U nonoflation signals and V color difference signals of the chroma signal. The comb filter is generally composed of delays, adders, subtractors, and bandpass filters. For still images, the comb filter is performed between the frame, i.e., three-dimensional comb filter. For moving images, comb filter is performed in intra, namely two-dimensional comb filter. In addition to special requirements, most digital television equipment or high quality digital television receivers use row delayed comb filters and bandpass filter cascading, which makes satisfactory images. quality. The use of a comb filter makes the image quality significantly. The interference spot caused by color strings and bright color is solved, interfering with pattern; eliminates the color edge creep caused by U, V, eliminating bright, color striped. 7. Attenuator is within the specified frequency range, a circuit used to introduce a predetermined attenuation. It is generally indicated by the number of ohmic numbers in the introduced decay and its characteristic impedance. The attenuator is widely used in the cable TV system to meet the requirements of multi-port on the level. Such as the input of the amplifier, the control of the output, and the control of branch decreases. Attenuator has two types of passive attenuators and active attenuators. The active atmosphere is combined with other thermal components to form a variable fader, and the device is used in the amplifier in the automatic gain or slope control circuit. The passive attenuator has a fixed attenuator and an adjustable failure.
The fixed attenuator consists of resistance, does not affect the frequency characteristics, commonly used T-type or π-type network; (related to the commonly used 75Ω impedance T type, the resistance data of the π-type different attenuation can be referred to the shared antenna television system); adjustable decay The device is used by the potentiometer in debugging and level adjustment. Require the input of the attenuator, the output impedance should match the interface, and there should be 75 euros in the cable TV system. The frequency characteristics of the attenuator must meet the frequency range requirements of the system, and the attenuation amount of the attenuation in the frequency range should be independent of frequency. Therefore, it is often composed of a resistance element. Different frequency ranges, the form of attenuators is also different. Useless coaxial attenuator; in the waveguide system, a diaphragm that is often absorbed electric field energy is declining; there is also a solid diode (such as a PIN diode) to make a waveguide or coaxial system in the microwave frequency band can be electrically tuning. Attenuator. Attenuators are commonly used in a variety of telecommunications devices and electronic instruments. 8. Equalizer In telecommunications equipment, the network used to correct due to different frequencies (i.e., transmission loss) and different phase differences. Correct the attenuation and frequency relationship, called "attenuation equalizer"; the correction phase difference and frequency relationship is called "phase equalizer". A equalizer often needs to be used in cable TV systems. The equalizer is usually connected in series in the circuit of the amplifier, which is inconsistent with the high frequency caused by balancing cable transmission, and the low frequency end signal attenuation is inconsistent. Because the attenuation characteristics of the cable increases with the increase of frequencies. Commonly used attenuating equalizers, also known as amplitude equalizers. Generally consisting of a coil, a capacitor, a resistor and other components. The characteristic impedance of the attenuation equalizer is equal to a value, its equalization value is the decibel difference of the decay between the attenuation amount between the low frequency reference points, the frequency characteristics of the equalizer just opposite the cable frequency characteristics, but the frequency low attenuation, high frequency The attenuation is small, and the opposite characteristic is used to equally act. The equalizer is also often made into a small piece of printing board, with a balanced size. Nine, the mixer combines two sets of different frequencies radio frequency program (signals) together to form a wideband radio frequency (signal) multi-channel output device as a mixer. In the front end of the cable TV system, the mixer is the distribution point of the system signal, that is, in the mixer input, all the technology-processed multi-channel RF signals, and then output the signal to the system network to the user in the mixer output. . The main technical requirements of the mixer. Working frequency: The mixer should be a wide band-type frequency to meet the requirements of the entire frequency band in the system. The mixer should be the channel type, the frequency of the mixed channels should meet the required mixed channel requirements; access loss: The smaller the access loss (insertion loss) when the signal is passed through the passive network. The input power of the mixer and the ratio of the output power is called the access loss of the mixer. Access loss is usually expressed by decibels. When used in decibels, the difference between the number of pieces of the input end level and the number of output terminals. Different mixer access is different; input and output impedance: In order to match each interface in the entire system, the input and output of the mixer should be 75 o'clock; the inputs are separated from each other; In the case, when either the mixer is added to the signal, the other input does not appear this signal, and the other input should not affect other inputs when there is an open or short circuit. But it is actually always a certain impact. In the case where each end is matched, an input is added to a signal, which is the difference between the signal level in the other input, that is, the mutual isolation between the mixer input, generally represented by decibels. . There are different requirements for different mixers, and generally require greater than 20 decibels. Ten, mutual modulation ratio (IM) Cable television system amplifier amplifier TV signals, due to the nonlinear effect of the amplifier (mainly secondary item), the transfer signal is mixed, the frequency or difference frequency of each other In the frequency range to receive the channel, the television receiver will generate interference, which is called intermodulation of each other.
Mutual modulation is closely related to frequencies. Intermodulation interference, it generates mexic or twill interference. The intermodulation ratio is defined as an IM = 20LG carrier level effective value / intermodulation product effective value national standard specified in IM ≥ 57dB, and 58 dB should be taken. XI, Intertrudility Modulation Ratio (CM) Cable TV system amplifier amplifier TV signals, due to the influence of nonlinear devices in the amplifier (mainly three items), the image carriers to receive channels are subject to others ( Interfering) The amplitude change of the modulation wave of the channel, which is called intersection modulation or cross-modulation. Common phenomena is an integration of interference channel images on the image background to be received. Sometimes the horizontal synchronization signal of the interfering channel is flipped on the image screen to which you want to receive, becoming a vertical white strip, and the left and right movements (fixed at the same frequency), as if the wiper of the car front window, it is also called "wiper interference" . The interty modulation is the modulation of the interference signal to the carrier of the useful signal. Defining intersection modulation: XM = 20LG The peak-peak-peak-to-peak-to-peak-to-peak modulation definition is defined in the peak-peak modulation definition, defining intersection modulation ratio (cm): cm = 20LG The peak-peak / measured carrier-made peak-peak-to-peak-to-peak-to-peak-to-peak-to-peak-to-peak national standard is 48dB. Twelve, the dispenser distributor is the most commonly used component allocated in the cable TV transmission system to allocate the components of the signal. Its function is to divide all the input signals into several outputs, usually two-fitting, three-allocation, quad-assisted, six-assigned, etc. The frequency of cable TV networks continues to increase, and the function is continuously strengthened, so the requirements for the dispenser are constantly increasing. The main technical requirements of the dispenser. Frequency range: The dispenser uses in the entire cable network, therefore should have a broadband frequency characteristic; input output impedance: the radio frequency interface impedance in the cable TV network should be 75 euros to implement impedance matching, so the dispenser input End and output impedance should be 75 o'clock; allocation loss: That is always hoped in the system to access the dispenser loss, the better. What is the amount of the distribution loss LS and the number of allocated road numbers N, in the ideal case LS = 10LGN, when n = 2 is a biser dispenser allocation loss is 3dB. In fact, in addition to the loss of the alignment signal, there is a part of the distribution device itself, and the total ratio is larger than the calculated value. For example, the two-dispenser allocated loss project, the value of 3.5 dB, 4 dispenser loss, is 8db; mutually separation: Isolation is also known as isolation. If a signal is added to one of the outputs of the dispenser, the difference in signal level is isolated from each other, generally requiring the dispenser output end isolation to more than 20 dB. The larger the isolation of the dispenser output, the interaction between the outputs of the dispenser, is small interference; standing wave ratio: the standing wave ratio is an important indicator that measures the quality of allocation network transmission, which represents the degree of impedance matching. Under ideal, the input impedance of the dispenser, the output impedance, and the impedance of the coaxial cable which are coaxial cables are completely equal. At this time, the stationary wave ratio is 1, and the standby wave ratio is often greater than 1. If the standing wave ratio is too large, the transmission signal generates reflection at the input of the dispenser, and the image quality is adversely influence, such as returning and so on. The dispenser is also divided into an over-energized distributor, outdoor distributor, indoor dispenser, and the like. Thirteen, a single voice channel, picking the sound with a microphone, using a speaker to play the sound, called a mono. In TV broadcasting, mono sound quality is poor, especially in terms of cultural programs, especially when live broadcast high-level music performances are very inferior.
In addition, the mono audio can only be broadcast in one language. This is not applicable to my country's multi-dialect, and it should be developed into two language (dual channels). It also creates conditions for stereo broadcast. . 14. Double-sound / three-dimensional utilization double-channel can realize two-channel TV sound, while playing two different languages, such as one way standard Mandarin; another local national language or dialect, and both can be free. select. You can also use standard Mandarin or national language; another way to use a foreign language, and both can be switched freely. For example, when playing the original foreign TV sheet, although the Chinese subtitles can be played on the TV screen, it seems to be not smooth, and the double companion can overcome the defects of the craft. The double channel creates conditions for stereo broadcast. Because people's binars can distinguish the distance and direction of each sound source, so the listening has a spatial sense (or three-dimensional sense). In the sound system, two or more sound channels are applied, so that the relative spatial position of the sound source that the listener feels close to the relative spatial position of the actual sound source, which is referred to as stereo. There are two-channel stereo, four-channel stereo, Dolby stereo, Dolby surround sound, Dolby AC-3 digital surround sound. Radio broadcasting using stereo technology is called stereo broadcast. Take a two-channel stereo broadcast as an example. Dual channel stereo broadcast is a two-channel sound signal corresponding to the left front and right front two orientation by one or two different frequencies. The audience uses a stereo radio with a two-channel playback system that can identify the relative position of the sound source to generate a stereoscopic sense; if a normal radio can also receive the same program content, there is no stereoscopic sense. In order to meet mono compatibility, most of the fifty frequency bands are used. It only uses a FM broadcast channel, sending "left to right" signal, subcarrier amplitude frequency band, and pilot delivery "left minus" signal with the modulated basic sound frequency frequency. In theory in order to obtain the best stereo, the ideal method is to use unlimited plurality of microphones to pick up the sound signal, and then communicate the sound to an unlimited multiple speakers and play with unlimited multiple sound channels. As long as the position of the speaker and the position of the microphone correspond, the playback sound can accurately reproduce the sound of the site, so that the audience has a three-dimensional sense of the immersive scene. Fifteen, surrounded by a stereo surround sound refers to the replay of direct sound and reflection sound to surround the listener. Therefore, the more speakers, the stronger the listener being surrounded. Dual channel stereo can only distinguish the relative position of the sound source. The four-channel stereo system adopts four microphones, four speakers. Two of the four microphones are close to the stage, pick up the direct signal of the stage, the other two away from the stage, pick up the reverberation signal reflecting ambient sound effect. The four microphones picked up signals are transmitted from four separate sound channels to four speakers. Corresponding to the position of the microphone, the speakers are the left, front right, rear left, and back, right; where the left, front right is used to play the direct sound of the stage, the left, and then right for playback reflect the environmental effect sound. The listener has a speaker due to its front and rear, not only in the horizontal direction, but also the feeling surrounded by the sound, thereby also known as the stereo. 16. Dolby AC-3 Digital Surround Ac-3 Technique originated in providing high quality sounds for high definition (HDTV). The AC-3 technology is developed by Dolby AC-1, Dolby AC-2. AC-1 reduces the number of channels by 4-2-4 multi-channel matrix (this can reduce the transfer capacity), then digital encoding is performed using incremental modulation (△ modulation) technology. Therefore, the compression multiple of AC-1 is twice. With the advancement of the sound coding technology and the digital signal processor (DSP), the AC-1 system develops the AC-2 system based on the conversion coding technology. While improving the quality, the compressed multiple is further changed to 4 times, but multi-channel Matrix processing technology is still retained.
AC-3 is developed based on AC-1, AC-2, which inherits many advantages of AC-2, such as window processing, transform coding, adaptive bit allocation, etc., can also overcome their shortcomings And limitations. The AC-3 has 5.1 channels, ie left, medium, right, left surround, right surround and 0.1 low effect sound channel, the left and right surround channels are separate channels, more field and realism . On the basis of Dolby AC-3 technology, there are currently 6.1 channels, 7.1 channel digital repayment systems. AC-3 is the sound system of the US HDTV, which has been recognized worldwide. Note: 4-2-4 is a four-channel recording when the recording is represented. When the recording is placed in the movie film, 4 channels are compressed by coding techniques, and when the sound is restored, still playback 4 sounds. Original sound. 17. Panda Residents (PANDA-1) US Wegener Communications designed a set of practical television sound demodulation circuit technology in the early 1980s, named "Panda-1" in the early 1980s Chinese translation "Panda-1" high-fidelity multi-language three-dimensional sounds) and has been obtained in the United States. This sound technology is an analog noise suppression system that is a normal sound, generally must generally be wide with a high frequency bandwidth of 280 kHz, and it utilizes half of the high frequency bandwidth 130kHz to transmit the baseband audio signal 15 kHz bandwidth. Compress the dynamic range of the audio signals with a specific ratio of several tens of times, compress to a very narrow frequency band width. In this way, each of the images can be provided with up to six audio channels at the same time to perform stereo or bilingual broadcasts, and can transmit independent radio programs at the same time, which means that three sets of stereo or six-way mono can be transferred on different frequencies. Tao. The PANDA-1 sound is used in analog channel and analog compression, so the sound quality is larger with the digital companion signal used, but because of the saving bandwidth, there are more channels. Receiving a PANDA-1 audio requirement receiver has an extended circuit audio carrier demodulator, otherwise the received sound is a high noise and high distortion. Any receiver with the PANDA-1 demodulation function can be selected as soon as the six sound or two-channel stereo, the screen is displayed, and the audio program is received. Eighteen, Lie Yin (NICAM) Nicam is an instantaneous pressure-expanded sound multiplex, which is a digital sound processing technology. The main feature is that the signal to noise ratio is high, the dynamic range is wide, and the sound quality is comparable to the CD. Therefore, Nicam is It is called Lyon, and the Lie is a commonly known as the radio and television audio. my country's ground broadcasting and satellite broadcasting TV sounds are modulated. Lyper is based on the original part of the sub-carrier frequency, and a digital sound sub-carrier is added, and the sound formation of the double carrier mode does not interfere with the original mono signal. Adopt AM-FM, FM-FM playback mode. Lisin mode has stereo mode, left, right channel; bisphon sound mode simultaneously transmits two speech from left and right channels, can also transmit two single-channel broadcasts, or all way to broadcast and all way data. The dedicated modulator is transmitted after transmitting it, then transmits it together with the television image signal and the analog audio signal. When receiving, you can listen to the digital three-dimensional sound program that is comparable to the CD with a dedicated Lisin demodulator. There are more than 20 kinds of international, Leiyin, my country uses Nicam, D Loys. The second sub-carrier 7.28 MHz is added on the basis of retaining the original analog FM components, and the quasi-instantaneous pressure-amplification coding technology is used. At present, in my country's central TV station, in the second set of program satellite transmission systems, NICAM-728 is used to insert the three sets of centralized people's radio stations. When the satellite digital sound broadcast signal is received, the satellite receiver needs to have a baseband output, which will be connected to the NICAM-728 receiver. After receiving a stereo signal after it is processed, it is convenient to obtain a high quality CCTV broadcast program signal. source.
