I. User needs
Our school is a "National 211 Project" key university. In order to improve teaching quality and student performance, it is necessary to make full use of the school's existing closed-circuit television system, introduce satellite television educational programs and live school demonstration classes. For this reason, after the school leaders negotiated, it was decided to build a set of multimedia closed-circuit multimedia closed-circuit television broadcast television live broadcast system.
Requirements are as follows:
1. Set up a multimedia demonstration class live broadcast site, and require the selection of domestic first-class equipment to ensure the quality of the demonstration class live broadcast.
2. Six sets of satellite TV educational programs are scheduled to be broadcasted, and it is required to be inserted in existing school cable TV programs.
3. The inserted multimedia closed-circuit television broadcast programs will not affect the original programs in the system under the premise of ensuring the viewing quality.
User demand analysis
The multimedia audio and video closed-circuit television live broadcast system is a school that takes a large auditorium, conference room or multi-purpose hall as the center venue or live broadcast center, or the automatic broadcast software of the TV station broadcasts audio and video programs automatically. Leadership speeches, large-scale activities of the school, and quality demonstration lessons are broadcast to various classrooms, which is an indispensable means of modern teaching practice for the whole school teachers and students to watch simultaneously.
The multimedia audio and video CCTV live system can also broadcast satellite TV programs as needed, so that important news, sports games, and central and local TV teaching programs can be watched at any time. The number of simultaneous broadcast channels is determined by the school according to specific needs. It can be easily extended in the design of this scheme.
The multimedia audio and video closed-circuit television live system can also use the DVD player to transfer the CD of quality education and teaching courses, which can make the process of education and teaching more vivid, vivid, easy to understand and remember.
Third, the design of the multimedia closed-circuit television insertion system scheme
3.1 Program Source Design
The live broadcast part selected the internationally renowned brand SONY integrated high-definition camera.
The educational program was broadcasted using a Gaussberg satellite receiving antenna, a PBI tuner, and a satellite receiving engineering machine as the receiving equipment. It broadcasted multiple international and domestic satellite education channels to meet the school's multimedia live teaching requirements.
3.2 Modulation Hybrid Design
In order to ensure the signal quality of the entire multimedia audio and video live broadcast system, and consider the transmission of closed-circuit television signals in the future system, the JB860 agile frequency adjacent frequency modulation host is selected as the RF modulation device for the multimedia live broadcast signal. VS-16 16-way passive mixer is selected as the mixing equipment. The modified equipment has the advantages of high reverse isolation and small mixing attenuation coefficient.
3.3 Transmission Design
Trunk line refers to the coaxial cable from the machine room to each building and the branch trunk in the building. It is placed in the weak current shaft and in the trunking. SYWV75-7 coaxial cable is used.
3.3.2 branch line
The branch line refers to the coaxial cable from the branch trunk line in the building to the distributor and the distributor to the terminal panel. SYWV75-5 coaxial cable is used.
3.3.3 Terminal line
The terminal line refers to the coaxial cable between the terminal panel and the dedicated agile frequency demodulator. We choose the coaxial cable of model SYWV75-5.
3.3.4 Mains Amplifier
The domestic first-class Maiwei brand trunk amplifier is selected as the trunk line amplification equipment, which has the characteristics of high amplification gain, small nonlinear distortion, stability and reliability.
3.4 terminal design
The use of high isolation advanced plastic user terminal boxes makes the user terminal boxes beautiful, generous and practical.
Fourth, the principle of multimedia closed-circuit television insertion system
4.1 Principles of the Multimedia Closed Circuit TV Insertion System
Install cameras, microphones, etc. in the school's multifunctional hall as the source of multimedia audio and video closed-circuit television live broadcast systems. The camera collects multifunctional hall video, the microphone collects multifunctional hall audio, or the satellite receiving system demodulates standard audio and video programs The input agile frequency adjacent frequency modulation host modulates the live broadcast program to the RF high frequency carrier, so that the live broadcast program can share the network transmission with the CCTV signal. The modulated live audio and video signals are mixed and multiplexed onto a coaxial cable through an adjacent-frequency mixer and closed-circuit television signals, and are input to a trunk amplifier to amplify the high-frequency carrier. The amplification gain is generally 0 to 30 dBuv. It is then sent to the school's coaxial branch distribution network and output to each classroom terminal panel.