Analysis of three transmission methods of broadcasting system and their advantages and disadvantages
Broadcasting can be basically divided into three categories: constant pressure broadcasting, FM broadcasting, and network broadcasting.
1. Constant pressure broadcasting (
Constant pressure transmission broadcasting is to directly amplify the audio signal and transmit based on the power signal. In order to reduce the transmission loss of the line, the 4～160 matching impedance is transformed to 100V constant voltage mode for transmission through a step-up transformer. After transmission to the terminal, the voltage is stepped down and converted to 4～16 speakers. The general transmission distance is tens of meters to Several hundred meters.
advantage:
Mature technology, simple structure, stable performance, easy maintenance, and cheap terminals. At present, it is widely used in stations, docks, schools, commercial and civil buildings.
Disadvantages:
1) Constant voltage transmission is affected by factors such as the bandwidth of the line's transformer, speaker size, and cable diameter. The frequency response ranges from 200Hz to 12kHz, and the distortion is ≤10%, so stereo transmission cannot be achieved.
2) The program capacity is small and cannot be addressed and controlled. One line can only transmit one set of programs.
3) The audio sources are basically analog audio sources, and digital format audio files cannot be played, and automatic playback and automatic control cannot be realized. Constant voltage broadcasting is designed according to the principles of power matching and impedance matching, and the capacity of the system is very limited.
2. FM radio
FM transmission broadcasting uses FM modulation to transmit audio signals to a high-frequency carrier, and uses the frequency change of the high-frequency carrier to describe the change of the audio signal. Different carrier frequencies can carry different audio programs at the same time. my country divides 87～108MHz into FM broadcasting band. At this stage, my country's urban broadcasting and closed-circuit broadcasting all use FM radio. FM broadcasting can be shared with cable television for transmission.
advantage
1) The audio range of FM broadcasting is 30Hz～7kHz, and the distortion is ≤0.7%. FM broadcasting has the advantages of wide frequency response, rich treble, strong anti-interference ability, and low distortion, and can be used for stereo transmission.
2) The technology is mature, the program capacity is large, and the price of supporting equipment is very low. The bandwidth of FM broadcasting is 16kHz. More than 60 sets of FM broadcasting programs can be simultaneously transmitted in this frequency band, which can meet the requirements of simultaneous broadcasting in multiple zones.
3) Good compatibility and scalability.
Disadvantages FM broadcasting is based on weak signal transmission, each receiving device must be an active device, that is, each speaker and terminal must be connected to a 220V power supply.
3. Webcast
Digital audio network broadcasting must be transmitted and played on the Internet to realize the functions and requirements of broadcasting.
The network audio broadcast is controlled by an IP network broadcast control host, a set of broadcast software or server software, which sends audio files to remote network terminals in the form of IP streams. Each terminal should have a fixed IP address and network module, A professional digital audio decoding device (software or hardware), power amplifier control unit. At present, manufacturers have begun to develop network audio broadcasting and have launched products.
advantage
1) Network broadcasting has been digitized and networked from program production to transmission. The system has a high signal-to-noise ratio and can achieve better sound quality. It can also be used for stereo transmission.
2) It is relatively easy to realize intelligent broadcasting. Ethernet itself is a set of two-way network. The timing, addressing, grouping and other functions of intelligent broadcasting can be easily realized by software on the Ethernet.
3) Multi-channel broadcasting can be realized if the network speed allows.
4) Realize interactive broadcasting.
5) Convenient management.
Disadvantages:
1) For the decompression of digital audio files, it must be PC+ special software or a special decompression chip, and each terminal must have its own IP address, which has a relatively high technical content.
2) The price is expensive. At present, there are no professional chip-level developers in China, and they can only decode with embedded microcomputers and dedicated decompression chips, which leads to higher product prices.
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