Coaxial cable structure to understand the structure of the coaxial cable to first understand the role of the cable, in the satellite television system, the signal from the satellite downlink received by the antenna, through the coaxial cable link to the set-top box, and then by the set-top box will be decoded The television signal is transmitted to the television so that we
Can see clear and smooth TV shows.
The "coaxial" of coaxial cable, as its name suggests, is that each part of the line is on an axis. From the cross section, it is a concentric circle. The structure of the coaxial cable, from the outside to the inside, is the sheath, the outer conductor (shielding layer), the insulating medium and the inner conductor.
Minute. Let's introduce the role of each part separately.
The jacket, that is, the outermost layer is an insulating layer, which plays a protective role. The outdoor cable should use black polyethylene with good weather characteristics. The indoor user cable should be light-colored polyethylene because of its aesthetic considerations. Outer conductor (shield), double outer conductor of coaxial cable
Re-acting, it is used as a transmission line of a transmission line, low-level transmission, but also has a shielding effect, the outer conductor usually has 3 kinds of structures. (1) Metal tubular. This structure uses copper or aluminum tape longitudinal welding, or seamless copper tube extrusion drawing, this structure
The form of the best shielding performance, but poor flexibility, commonly used in the trunk coaxial cable. (2) Aluminum plastic composite tape vertical bag lap. This kind of structure has good shielding effect, and the manufacturing cost is low, but because the outer conductor is a circular tube with a longitudinal seam, electromagnetic waves will pass through the gap.
Leakage should be used with caution. (3) Combination of woven mesh and aluminum-plastic composite tape longitudinal package. This is based on a single braided mesh structure. It has the characteristics of good flexibility, light weight and reliable joints. Experiments have shown that using a reasonable composite structure, there are shielding properties
Greatly improved, the current structure is widely used. Insulation medium, followed by insulative layer made of foamed material, the insulation medium can use polyethylene, polypropylene, polyvinyl chloride (PVC) and fluorine plastic, etc. The common insulation medium is small loss,
Good performance of polyethylene. The inner conductor, the innermost copper wire, acts as a conductor and transmits a high level, using the skin effect of the high-frequency signal (repulsion between charges, the charge is distributed on the surface of the conductor), and an empty copper tube can be used. Copper plated aluminum rods are also available
Copper-clad steel wire is used for customer networks that do not require power supply. Copper-clad aluminum wire is recommended for distribution networks or trunk lines that require power supply. This can ensure the transmission performance of cables and meet the requirements for power supply and mechanical performance, thus reducing the need for power supply. The weight of the cable also reduces the electricity
The cost of cable. Some inferior ones may use iron cores, which can be verified using magnets at the time of purchase. Copper-clad iron is allowed, which can be seen.
In the television system, according to the location of the coaxial cable application, it can be roughly divided into three types.
1. Mains cable: The thick cable whose insulation outer diameter is generally more than 9mm requires less loss and less flexibility.
2. Branch cable: The medium and thick cable whose insulation outer diameter is generally more than 7mm requires low loss, but also a certain degree of flexibility.
3, user distribution network coaxial cable: its insulation diameter is generally 5mm, loss requirements are not the main, but requires good flexibility and indoor unity of straight coordination.
In the specific application, if the length of the wiring is too long and the signal attenuation is serious, it is a good idea to choose a thicker coaxial cable.
Always listen to the -7, -5 line. Do you know what it means? This also needs to start with the naming of coaxial cable in order to make it easier for everyone to see the structure type of the coaxial cable model. The following gives the method and the meaning of the code for the unified model of our cable.
reference. Coaxial cable designation usually consists of four parts.
The first figure behind the national standard is the characteristic negative resistance. The characteristic negative resistance is determined by the structure. It has nothing to do with the conductor resistance. It can be understood as the wireless long-term impedance of the cable. Commonly used are 75Ω, 50Ω, and 93Ω.
The second figure is the inner diameter of the outer metal. The larger the number, the thicker it is. In order to ensure a stable characteristic impedance, the inner conductor will also become thicker.
The third number is the serial number. The difference between each serial number depends on the manufacturer's description. There is no uniform requirement.
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