Views:4 Author:Judy Chang Publish Time: 2021-05-18 Origin:Site
Cable television is also called CATV. It is a television system that uses cables or optical cables as the transmission medium to transmit television signals to users through a television distribution network.
Advantages of Cable TV System:
1. The image quality is good, and there are no problems, such as ghosting and spatial clutter interference from open-circuit emission;
2. The program source is rich, not only can rebroadcast local open-circuit TV programs, self-run programs, but also forward satellite TV programs, etc.;
3. It can transmit digital information in two directions, making the TV system develop in the direction of a two-way interactive, multi-functional, and multimedia information communication network.
Transmitted system of CATV
The TV signal transmitted from the main line is distributed to each user through the cable. For two-way cable TV, the upstream signal needs to be correctly transmitted to the front end. The main equipment of the distribution system is: splitter, TAP, line extension amplifier, distribution amplifier and For user terminals, there are also modems and data terminals for two-way television systems.
The TV signal input from one channel is divided into several channels and output is mainly used in the front end, trunk line, branch line and user distribution network; ordinary households have multiple TV sets, which can be used. It can divided the wired signal that enters the house into multiple channels and output them to the TV. The output signals are isolated from each other and crosstalk will not occur. Compared with the input signal, the output signal of each channel will have a certain attenuation, and the attenuation is the same. Commonly used are 2,3,4,5,6,8,10,12,16
Distribution function divide the power of the input signal evenly into several channels.
Isolation-the signal from one output terminal has no effect on the other output terminal.
Matching effect-the impedance of the output end and the input end are both 75 ohms.
Commonly used distributors: two distributors, three distributors, four distributors and six distributors;
The output end of the distributor cannot be open circuit (not connected to the load), otherwise it will cause a serious mismatch of the input end and also affect other output ends. Therefore, when the distributor has free output, it is necessary to connect a 75 ohm load resistor.
The TAP port is also called the BR port, which means branch. If you need to connect branch devices in series, you need to use a branch. Its form is similar to that of a splitter. But its output has only one OUT port and the rest are several BR ports. The attenuation of the OUT port is very small, which is the connection interface between the splitter and the splitter. The signal attenuation of the BR port is relatively large, so it can no longer be used as a trunk connection of the splitter in series, and is generally directly connected to the terminal.
Function: Part of the signal is separated from the transmission trunk line or distribution line with a small insertion loss, and sent to each user after attenuation.