I. User needs
Our school is a senior middle school. In order to meet the requirements of the college entrance examination foreign language listening test, a cable-addressable intelligent broadcasting system needs to be constructed. The school has now built a closed-circuit television system, and the decoration is intact, and the road surface is hardened. The construction and upgrade of campus broadcasting is required without destroying the existing environment. The specific requirements are as follows:
There are 85 classrooms, one FM speaker per classroom.
The campus has 10 fixed pressure columns, which require FM to constant pressure.
The playground has 6 fixed-pressure sound columns, which require FM to constant pressure.
Requires 4 simultaneous transmissions.
Requires point-to-point addressing and co-cable transmission with CCTV.
Can be arbitrarily divided into grades.
Ability to play campus radio programs automatically.
User demand analysis
According to the user's current situation and specific requirements, we choose the campus cable addressable intelligent broadcasting system of Beijing Hite Weiye Technology Co., Ltd. This system uses FM frequency modulation technology, computer technology, single-chip microcomputer technology, etc. to integrate audio and control signals with The cable television signals are transmitted by common cable, which can achieve the modern campus broadcast implementation mode of automatic program broadcasting, automatic management of peripherals, and automatic control of terminals.
Third, the campus wired addressable intelligent broadcast function features
3.1 Campus wired addressable smart broadcast function
Maintaining order: The system has the basic functions of traditional constant-pressure campus broadcasting, such as: time to get up, exercise, class, after class, lights out, etc., can be set to ring automatically at regular time according to needs, to maintain the order of teachers and students teaching life.
Background music: In the free time after class, on Saturdays and Sundays, you can play news webcasts, song blessings, light music, pop songs, etc. as needed to effectively alleviate the pressure on teachers 'and students' lives, teaching and learning, and create an active and dynamic campus. Time and space.
Multi-channel broadcasting: As the 88-108MHz frequency band resources in the coaxial cable are reserved for FM broadcasting, a single cable can be used to transmit up to dozens of sets of broadcasting programs to meet the needs of independent campus broadcasting of grades.
Addressing broadcast: The system has an addressing broadcast function, which can automatically or manually control the receiving status of each classroom and campus receiving terminal (FM speaker / FM repeater) through software. The receiving terminal can also be arranged into groups at will, and can be played automatically or manually through software control.
Unified broadcasting: The system can perform unified collective broadcasting according to the needs of teaching, and all speakers play the same program, so that schools can perform collective broadcasting, school meetings, and unified audio teaching.
Foreign language teaching: Recently, there is a strong demand for foreign language talents. The country will develop students' foreign language ability from written to written and comprehensive listening. As a result, foreign language listening teaching, training, and examination have become new tasks undertaken by campus broadcasting. The system can meet the needs of a single class. , Class grouping, and foreign language broadcast requirements for all classes.
Broadcast gymnastics: The system can arrange the eye exercises, broadcast gymnastics, marches, sports songs and other tracks, and set automatic or manual playback as required, which can meet the requirements of students' eyesight protection, body, and sports games.
Emergency broadcasting: Schools are places for teaching and education, with a large population. The system has the function of emergency broadcast evacuation of any class combination for teachers and students in case of emergencies, which enables the school to protect the safety of teachers and students to the greatest extent in the event of an emergency.
3.2 Campus Wired Addressable Smart Broadcast Features:
Variety of programs: The system is compatible with various program playback equipment such as DVD, MIDI, computer, radio head, gramophone (there is more use in theaters), to meet the current format of teaching audio playback.
Auto play: Supports the scheduled playback of tracks on a weekly basis. The system can automatically play tracks on time according to the scheduling program and automatically manage the status of the playback terminal.
Autonomous management: The system organically integrates computer control technology, single-chip microcomputer technology, and software programming technology to fully realize the autonomy of playback, peripherals, and terminal management, saving manpower and material resources.
Co-cable transmission: The FM carrier is used to modulate the audio and control signals, and the audio and control signals are carried on the high-frequency carrier, which can be transmitted on the same cable as the cable television, which greatly improves the utilization of transmission resources.
Multiple listening: The system supports multiple answering methods. You can use FM speakers to listen directly, or you can demodulate the signal by FM repeater and then amplify the power with ceiling speakers, wall-mounted speakers, outdoor sound columns or modeling speakers.
Expansion at will: 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 receiving field strength requirements. Therefore, the expansion terminal does not need to re-lay cables or replace power amplifiers, and can be connected from the coaxial network at will on the basis of meeting the field strength requirements.
Design of campus cable addressable intelligent broadcasting scheme
4.1 Sound source design
Mainly by the audio source (analog source from the digital audio source output by the host, digital tuner, microphone, etc.), audio matrix (audio signal switching equipment), FM modulator (audio signal modulation equipment), intelligent coding controller (control signal modulation Equipment), mixers, etc.
4.2 Broadcast control design
The coding controller and computer are combined to intelligently and automatically control the entire broadcast system. With coded remote control, you can freely control the broadcasting of a certain point or area on the interface, and you can also control it manually.
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 an optoelectronic hybrid network (optical and coaxial cables are transmitted together).
4.4 Receiving Design
Comprehensive building, training building and practice workshop classrooms use crystal frequency stabilized indoor FM speakers to listen.
The restaurant adopts "FM receiver + wall-mounted speaker" for FM to constant pressure playback.
The apartment uses "FM receiving controller + constant voltage power amplifier + ceiling / wall-mounted speakers" to convert FM to constant pressure listening. The apartment can perform on-site secondary broadcasting and timely broadcast dormitory management information.
Outdoor places use the "FM receiving controller + constant pressure amplifier + outdoor waterproof sound column" FM to constant pressure mode listening, outdoor sound column adopts aluminum alloy structure, fully waterproof and dustproof.
V. Principles of Campus Wired Addressable Smart Broadcast
5.1 Principles of Campus Wired Addressable Smart Broadcast
DVD, microphone and other analog audio sources broadcast analog audio, sent to the mixer for mixing, volume adjustment, audio modification and other output composite audio signals, and digital tuner, intelligent broadcast control host and other audio input audio matrix switchers for audio After the signal is switched, it is input to the FM modulator to modulate the FM high-frequency carrier signal, and 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 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 RF form. The terminal can play the sound through the FM speaker, or use the FM power amplifier to demodulate the audio signal and then play it through the fixed pressure column after power amplification. The controller demodulates the FM signal and sends it to the constant-voltage power amplifier for playing through lawn speakers and constant-voltage speakers.