What Is a Feed Line?

The feeder is also called a cable. It plays the role of transmitting signals in a cable television system. It passes the signal received by the antenna to the front-end system, and the signal output by the front-end is also transmitted to the television of each user by the cable. Therefore, the quality and type of the feeder is an important factor that directly affects the receiving effect and signal transmission quality of the cable television system.

The feed line is the signal line connecting the early TV and the outdoor antenna. The flat shape is generally double wire. The wire body is insulated plastic. There is no shielding layer on the outside. Nowadays, due to the popularization of cable television, the TV signal line is completely replaced by the coaxial cable.

The feeder includes the antenna's lower lead and the system's main line, branch line, branch line, subscriber line, and so on. There are three types of feeders used in cable television systems: flat feeders, coaxial electrical environments, and optical cables. The most commonly used are coaxial cables.

Its main task is to effectively

In a cable television system, the connection between components and components, and components and feeders must be impedance-matched; otherwise, high-frequency signals will be reflected when they are transmitted in the feeder, which increases the energy loss of the signal during transmission. On the other hand, this reflected wave will affect the transmission quality of the signal and cause ghosting of the image when the user views it. Therefore, impedance matching is an important issue in the design, installation and use of cable television systems.

Generally speaking, the antenna and the feeder have a matched connection, which means that the connection between the two has the following three conditions:

(1) The impedance of the antenna is purely resistive (that is, the reactance is 0), so that the lower lead of the antenna can obtain as much energy as possible from the antenna, and the signal transmission efficiency is improved.

(2) The impedance of the antenna feeding end should be equal to the characteristic impedance of the feeder. In the case where the two are not the same, the transformation of different impedances can be achieved through an impedance transformer or other methods.

(3) The feeding end of the antenna is a balanced output. If a parallel feeder is used as the lower lead of the antenna and the impedance of the two is the same, in this case, it can be directly connected. If a coaxial cable with an impedance of 75 is used as the down lead, a balanced-unbalanced conversion is also required.

The maintenance of antenna feeder system should focus on spring inspection and autumn inspection. Carefully and comprehensively check the main feed pipe, rheostat, and distribution cable. Connection and sealing of various parts of the feeding head and jumper. For routine maintenance, you can observe the standing wave ratio indicated on the output power meter of the TV transmitter (normally S <1.1). For maintenance and repair work on the tower, you can start with the fixing of the main and branch cables. The fixed jumper is used. Copper screw, and make the jumper and the feeding head in good contact. For the rheostat, carefully check the sealing of each connection part and the distribution cable head. Every summer, check to prevent water ingress. deal with. ^[3]