[Photos] The development and current situation of campus radio

Campus radio, as the name implies, is a broadcasting system on campus, which originated from cable radio. However, in recent years, due to the widespread application of computer technology, people have also included campus radio and multimedia systems in the scope of campus radio, so a new concept of campus radio has been formed. In the early 1970s, many colleges and universities opened campus radio stations with very simple equipment, using tube amplifiers, installing tweeters outdoors, and reed speakers in classrooms. At that time, there were only two purposes: one was to enrich the cultural life on campus, and the other was to hold radio conferences. After the 1990s, with the improvement of audio-visual teaching methods, cable radio and television networks and wireless small FM radio appeared on campus. After entering 2000, campus radio has developed very rapidly. A gigabit Ethernet LAN multimedia teaching system and digital broadcasting system that is ahead of other industries has sprung up on campus, becoming an important means of audio-visual education. The Ministry of Education attaches great importance to the construction of campus networks. In accordance with the "Decision of the CPC Central Committee and the State Council on Deepening Education Reform and Comprehensively Promoting Quality Education" and the "Action Plan for Education Revitalization in the 21st Century", the Ministry of Education issued Document No. 16 of the Ministry of Education (2001) "Guiding Opinions of the General Office of the Ministry of Education on the Construction of Primary and Secondary School Networks", which puts forward specific requirements for the design and construction of campus networks, requiring that the network design should adopt the internationally accepted TCP/IP protocol. It also puts forward specific requirements for the equipment used, which should be advanced, practical, open, flexible, developable, reliable and secure. It points out the direction for the construction and development of school networks.

1. Equipment used for campus broadcasting: There are many types of equipment involved in campus broadcasting, but they are nothing more than the following types:

1. Cable broadcasting:

Wired broadcasting is mostly used for English listening practice and examinations. It is mostly used for physical exercises outdoors. Its characteristics are reliable transmission, strong resistance to external interference, and good consistency of sound source. Wired broadcasting is a way of transmitting broadcast signals using twisted pair cables. It transmits audio signals. It generally uses 100v constant voltage transmission on campus and 240v for long-distance transmission. Amplifiers are divided into tube amplifiers and transistor amplifiers. At present, the technology of transistor high-power amplifiers has matured. Schools use high-power transistor amplifiers of more than 300w. Constant voltage output: domestic machines generally have 20 outputs (for connecting 16Ω25w tweeters), 120v/240v outputs (for line transmission, connecting to speakers in classrooms), and imported amplifiers have 110v/70v outputs, generally using 100v line transmission, connecting to speakers in classrooms. The input terminal of the amplifier is generally a line input method, connected to the preamplifier or mixer. Some amplifiers also have microphone input ports. The sound source generally uses microphones, VCDs, recording decks, digital tuner receivers, computers and other equipment. Tweeters are used in the campus (but they must be equipped with line transformers), and some use sound columns, with a power of 15w-30w. Special speakers are generally used in classrooms, with a power of 5w-15w and a constant voltage input of 100v-120v.

Three new technologies in cable broadcasting:

(1) Zone broadcasting: Zone broadcasting is to selectively broadcast to different areas in a broadcasting room. One way is to use multi-point wiring and the switching switch in the room. Its advantage is that the broadcasting room can broadcast different areas at the same time. The disadvantage is that the wiring is troublesome. The second way is site broadcasting. An encoder is used in the room, and a decoder is installed on each speaker. The group on and off of the speakers can be controlled by the coding button in the room, which is more flexible. The disadvantage is that only one signal source can be used for multiple areas at the same time, and the investment is relatively large. The third way is to use cable TV (CATV) network for multi-frequency broadcasting, which is to modulate the audio signal and then transmit it through the cable TV network. Within an 8MHz TV channel bandwidth, hundreds of broadcast signals can be transmitted to broadcast different classes. This is a more practical campus broadcasting method.

(2) The signal source is a computer. The tape, VCD or other signal sources are recorded in the computer and converted into the same format and stored in the computer's hard disk for sequential and timed playback, and the amplifier or transmitter is automatically turned on and off. This reduces distortion, reduces wear and tear, and achieves the purpose of automatic playback.

2. Wireless FM broadcasting: This method sends the audio signal to the transmitter for modulation and amplification, and then transmits it into the air through the antenna. Students receive it through wireless headphones, and the wireless sound column is used to play it in the campus. This is a way of propagating through electromagnetic waves. Its advantage is that it saves the trouble of wiring. The disadvantage is that it is easily interfered by air clutter. The transmitter has different power levels. Generally, 2w-30w is required on campus.

The power requirement in the classroom is not more than 0.5w, otherwise, excessive power will easily cause interference. For antenna requirements, omnidirectional outdoor antennas are used in the campus, and the height requirement is higher than all buildings on the campus. The transmitter in the classroom should use the pull-rod antenna on the machine, and all should be pulled out when in use. The oscillation modes of the transmitter are: frequency synthesis, crystal and inductive oscillation. The more advanced models are frequency synthesis, characterized by stable frequency and convenient adjustment. FM broadcast automatic receivers are mostly used for sound columns and tweeters, and are generally used for broadcasting in the campus. The oscillation mode is similar to that of transmitters. There are three anti-interference methods. One is to use the squelch level to control automatic power on and off. The characteristic is that the circuit is simple, and the disadvantage is that it automatically turns on when it is interfered with by the same frequency. The second method is to use the pilot signal of the stereo transmitter to control the power on and off, which effectively controls the same frequency interference. The third method is to use the codec method to turn on and off, avoiding interference, and also realizing the power on and off of the control area and the control point. Wireless headphones are available in two types: tuning type and point frequency type. Each student is equipped with one for listening training.

New Technologies in Wireless FM Broadcasting:

(1) Broadband transmitter: This transmitter can use one frequency point to transmit hundreds of audio signals at the same time. It is a new type of campus broadcasting equipment. The disadvantage is that the receiving equipment is expensive. (2) Frequency synthesis FM broadcast automatic receiver and amplifier using infrared remote control, the characteristic is that the frequency and volume of the receiver can be controlled by remote control. It can also be adjusted by remote control in the transmitter room. (3) Wireless site selection control device: It is a way to realize remote control power on and off, which can be turned on and off for groups, slices, or points.

3. Data broadcasting: It is a way of multimedia broadcasting using Gigabit Ethernet LAN, and it is a new broadcasting method. The transmission process is completely digitalized. It consists of a server, a classroom data terminal box and other user computers to form a comprehensive multimedia teaching network, and its functions can be increased or decreased according to user requirements. The functions currently realized include distance education, courseware management, electronic book management, campus IC card management, principal evaluation system, data broadcasting, time automatic reminder system, etc. Here we focus on the classroom data terminal box. The data terminal box is a small computer with E-link data transmitter as the main body. Its feature is that it does not require complicated operation processes in the classroom. Its line connection interface connects to the connection line of the Ethernet LAN. Its input port can be connected to the mouse, keyboard, infrared remote control, camera, audio input device, etc. The output end has analog audio output, video output, data output, which can be remotely controlled and telemetered and is equipped with a USB port. The digital broadcast teaching system has replaced the traditional teaching method and is the development direction of electronic teaching.