Feed lines, also known as cable cables, play a role in transmitting signals in multiple fields, including cable television systems. Through them, the signals received by the antenna are transmitted to the front-end system, and the signals output by the front-end are also transmitted to each user's television through cable cables. Therefore, the quality and model of the feeder are important factors that directly affect the reception effect and signal transmission quality of the cable television system.

Characteristic impedance
In a cable television system, all components connected by cables must achieve impedance matching. Therefore, the characteristic impedance of coaxial cable is an important technical parameter to be considered when designing and installing the system.
 
The characteristic impedance of a coaxial cable is determined by the diameter of the conductor and the medium between the conductors, and is independent of the cable length.

Attenuation characteristic

The attenuation characteristic refers to the magnitude of loss when coaxial cables transmit television signals. The transmission line of a cable television system usually uses a coaxial cable with an impedance of 75 Ω. The transmission of television signals in the cable requires attenuation, which is related to the diameter of the cable conductor, cable length, dielectric material, and frequency of the transmission signal. The larger the diameter of the cable conductor and the lower the frequency of signal transmission, the smaller the attenuation, and vice versa, the greater the attenuation. So when TV signals are transmitted in cables, there are two situations: the same frequency signal is transmitted in cables of the same model and length, and even if the cable length is equal, the attenuation of the signal level is not the same; Signals of different frequencies are transmitted in cables of the same model and length, and the attenuation is also different.

temperature characteristic 

The attenuation of the cable increases with the increase of temperature, which is called the temperature characteristic of the cable. The temperature coefficient of a general cable is 0.2% dB/℃, which means that when the temperature increases by 1 ℃, the attenuation of the cable increases by 0.2% from the original attenuation. When transmitting signals over long distances, temperature compensation must be carried out.

Return loss

Echo loss is an increase in reflected waves and attenuation caused by uneven impedance of the cable, which has a significant impact on the clarity of the image. The reasons for echo loss are related to the quality of the cable itself, as well as improper use and maintenance, mainly including:
(1) Deviation or material deformation in the structural dimensions of cables during the production process;
(2) During installation, the cable is bent at right angles or flattened at the corners, causing structural deformation;
(3) The cable is subject to moisture, high temperature and other factors that cause material deterioration, resulting in changes in characteristic impedance.