1. User needs Our school is a senior middle school. In order to meet the requirements of the foreign language listening test of the college entrance examination, it is necessary to build a cable addressable intelligent broadcasting system. The school has now built a closed circuit television system, and the decoration is intact, and the road surface is hardened. It is required to upgrade the construction of campus broadcasting without damaging the existing environment. The specific requirements are as follows:
There are 85 classrooms, one FM speaker in each classroom.
There are 10 constant pressure sound columns on campus, which require frequency modulation to convert to constant pressure.
There are 6 constant pressure sound columns in the playground, which require frequency modulation to transfer to constant pressure.
It is required to transmit 4 sets of programs at the same time.
Requires point-to-point addressing and shared cable transmission with closed-circuit television.
Can be broadcast in any grade.
Able to automatically broadcast campus radio programs.
2. Analysis of user needs According to the current situation and specific requirements of users, we choose the campus common cable broadcasting system of Beijing Haite Weiye Technology Co., Ltd. This system uses FM frequency modulation technology, computer technology, single-chip technology, etc. The signal and the cable TV signal are transmitted on the same cable, which can achieve the modern campus broadcasting implementation mode of program automatic broadcast, peripheral equipment automatic management, and terminal automatic control.
3. Features of campus common-cable broadcasting. Variety of programs: The system is compatible with various program playback devices such as DVD, MIDI, computers, radio heads, phonographs (more used in theater schools), etc., to meet the current format of teaching audio playback.
Auto-play: Supports playing tracks to schedule play schedule in units of weeks. The system can automatically play tracks on time according to the schedule program and automatically manage the state of the playback terminal.
Management autonomy: The system organically integrates computer control technology, single-chip technology, software programming technology, etc., fully realizing the autonomy of playback, peripherals and terminal management, saving manpower and material resources.
Co-cable transmission: Adopt FM carrier to modulate the audio and control signals. Carry the audio and control signals on the high-frequency carrier, which can be transmitted on the same cable as the cable TV, greatly improving the utilization rate of transmission resources.
Multi-listening: The system supports multiple listening methods. You can listen directly with FM speakers, or you can demodulate the signal through the FM converter and then amplify the power to listen with ceiling speakers, wall speakers, outdoor sound columns or modeling speakers.
Random expansion: There are two requirements for the receiving terminal to play the track normally, one is to have the system power supply requirements, and the other is to have the signal reception field strength requirements. Therefore, the extension terminal does not need to re-lay cables or replace the power amplifier, and it can be arbitrarily connected from the coaxial network on the basis of meeting the field strength requirements.
Fourth, the campus common cable broadcasting scheme design
4.1 Audio source design is mainly composed of audio source (analog audio source from digital sound source output from the playback host, radio head, microphone, etc.), audio matrix (audio signal switching device), frequency modulator (audio signal modulation device), intelligent broadcast control host (control Signal modulation equipment), mixer, etc.
4.2 Broadcast control design Combining the coding controller and the computer, the entire broadcast system is intelligently and automatically controlled. With coded remote control, you can freely control the broadcast of a certain point or area on the interface, or you can manually control it.
4.3 Transmission design It consists of a closed-circuit television coaxial network (mainly composed of coaxial cables, branch distributors, coaxial connectors and amplifiers) or a photoelectric hybrid network (common transmission of optical cables and coaxial cables).
4.4 Reception design The indoor building FM speakers of crystal building stabilized frequency processing are adopted in the comprehensive building, training building and practice workshop classroom to listen.
The restaurant adopts "FM receiver + wall-mounted speaker" FM to switch to constant pressure to play.
The apartment selects "FM receiving controller + constant voltage amplifier + ceiling / wall horn" FM to constant voltage listening, and the apartment can perform on-site secondary broadcasting to broadcast dormitory management information in time.
Outdoor places use the FM to receive controller + constant voltage amplifier + outdoor sound column FM to constant voltage mode for listening. The outdoor sound column is made of aluminum alloy structure, which is comprehensively rainproof and dustproof.
V. Principles of Campus Common Cable Broadcasting 5.1 Principles of Campus Common Cable Broadcasting Analog audio sources such as DVDs and microphones broadcast analog audio and are sent to the mixer for output, mixing, volume adjustment, audio modification and other composite audio signals, and digital tuner, Intelligent broadcast control host and other audio input audio matrix switcher to switch the audio signal, and then input to the FM modulator to modulate the FM high frequency carrier signal, then sent to the mixer to multiplex the frequency into the CATV coaxial network.
The intelligent broadcast control host sends an RS-232 control signal to the encoding controller to control the encoding and modulation, and then sends it to the mixer to perform the same frequency modulation with the audio.
The cable FM broadcast signal is transmitted in the CATV coaxial network in the form of RF. The terminal can play sound through the FM speaker, or use the FM power amplifier to demodulate the audio signal and play it through the fixed-pressure sound column after power amplification. It can also be received through FM The controller will demodulate the FM signal to the constant voltage power amplifier to play through the lawn speaker and constant pressure speaker.
5.2 Schematic diagram of campus common cable broadcasting
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