1. Do not use counterfeit and shoddy coaxial cables, because counterfeit and shoddy products often cut corners and pass off inferior materials during production. The product quality is poor and the technical performance cannot be guaranteed, such as internal and external conductors, insulation media, etc. The quality of the materials used is poor, and various parameters are inaccurate, resulting in too large deviations in characteristic impedance, too large attenuation constants, poor frequency characteristics, poor temperature characteristics, poor shielding performance, etc.
2. Do not use the wrong characteristic impedance. Characteristic impedance is an important technical parameter of coaxial cable. Commonly used ones are 75Ω, 50Ω, etc. Impedance mismatch in use will bring many shortcomings, such as a decrease in the signal-to-noise ratio of the transmitted signal, ghosting of the image or rough and sparse images, etc. Moire interference deteriorates the frequency characteristics of the system and increases the data error rate in the data transmission system.
3. Improve the installation quality of cable ends and cable joints. When the end of the coaxial cable is connected to components such as junction boxes and amplifiers, the connection quality of the outer conductor (mainly braided mesh) cannot be ignored. If the connection is loose or broken, the signal level will be significantly reduced. There is often an obvious horizontal black band in the middle of the TV screen, and a vertical interference band that slowly moves to the left. The system is also easily affected by nearby power frequency and radio frequency interference; when the contact resistance between the outer conductor and the connector is too large (such as oxidation at the outer conductor connection, rust on the connector, etc.), reverse attenuation characteristics will occur. The attenuation band will be greater at the low end; improper coaxial cable assembly at the connectors and connection points of the cable can cause connections. The characteristic impedance changes greatly, causing reflection and standing wave interference.
4. Prevent coaxial cables and power lines from being interfered in parallel. Transmission lines, power transformers, motors, industrial electrical equipment and various household appliances are strong sources of electromagnetic pollution. When wiring, the coaxial cable cannot be parallel to the power line, nor can it pass through the same pipe. It's best to stay away from electrical equipment. And its wiring, this can avoid the above interference to a certain extent, and can also prevent damage caused by leakage, overheating and fire of the power cord.
5. Strengthen moisture-proof and waterproof measures. In open air and places with water, amplifiers, branch distributors and other equipment must be installed with waterproof boxes; the joints of coaxial cables should be made with waterproof bends (arc downward curved paths) at the near end to prevent water droplets from flowing along the cables. When entering circuits such as joints, the cable ends (joints) should be coated with sealant to make them waterproof; the main way for moisture and water vapor to invade the cable is through the head and sheath of the cable, so the sheath cannot be inspected and maintained. Negligence, if the sheath is damaged, bandage it in time.
6. Prevent the separation of the inner and outer conductors when connecting. Coaxial cable is a transmission line with a special structure. The inner and outer conductors have specific structural relationships and functions, and the circuit connections also have specific connection methods. The inner and outer conductors cannot be used interchangeably, otherwise normal signals will be affected. transmission without satisfactory results.
7. Do not reserve too many lines. The attenuation of the signal in the cable increases with the length of the cable, usually 2dB attenuation per 10m of cable, so you want the cable path to be as short as possible and not to reserve too much during wiring. It is beautiful, and the reserved cables are rolled into small discs and then fastened with wires, which increases the attenuation of the signal and changes the frequency characteristics of the system, resulting in poor performance in the high-frequency band of the signal, which is reflected in the reception effect of cable TV . , the reception effect in the UHF band is poor.
8. It is strictly prohibited to use sharp objects to pierce the cable to steal signals. In order to steal TV signals, some people use pins, sewing needles or small nails to pierce the inside of the cable, causing a stable or unstable short circuit between the inner and outer conductors of the cable, thereby generating a large amount of current. Signal attenuation on coaxial cable lines affects adjacent branches and causes cable TV signals to leak outward. When rain or moisture penetrates the cable through the needle holes, the impact and loss will be greater.
9. The influence of high temperature cannot be ignored. According to the temperature characteristics of coaxial cables, when the ambient temperature increases, the metal (inner and outer conductors) losses and dielectric losses of the cable will increase. For every 10°C increase in temperature, the attenuation of the coaxial cable will increase by about 0.2%. Therefore, when wiring, try to keep the coaxial cable away from high-temperature heat sources and high-temperature environments. When the temperature rises excessively, signal quality may degrade and system stability may be destroyed.
10. Prevent mechanical damage. Coaxial cable consists of two isolated concentric conductors, an inner and an outer conductor, with the axes of the inner and outer conductors coinciding. This physical structure determines a series of unique properties of coaxial cables. If external force causes mechanical deformation of a coaxial cable, it is equivalent to destroying the physical structure, which will inevitably change its electrical parameters, degrade its main characteristics, and affect the signal quality. In order to prevent mechanical damage to coaxial cables, the following points must be noted during planning and construction:
① It is strictly forbidden to fold the coaxial cable into a steep angle during installation. The cables should be arranged in an arc at the corners, and the turning radius should not be less than 5 times the outer diameter of the cable;
② When the cable is laid out in the open, it is strictly prohibited to use various metal products as clamps to fix the cable. Instead, plastic clamps specially designed to fix coaxial cables should be used, and the type of clamp must match the outer diameter of the cable. coaxial cable. Neither too big nor too small is appropriate;
③ Ensure the safety of coaxial cables during construction, and pay attention to anti-smashing, anti-pressure, anti-collision, anti-extrusion, and anti-puncture;
④The mechanical strength of coaxial cable is limited, so it should not be pulled forcefully during construction and installation. When laying long distances, pulleys should be used at corners to reduce traction, and talcum powder should be placed inside the pipe to reduce friction during cable laying;
⑤ Lay coaxial cables on indoor and outdoor walls and cylinders such as corridors and corridors. PVC pipes should be used for pipe laying. When burying across roads, they should not be buried directly or only protected with plastic pipes. laid in zinc pipes.