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What is the main difference between video cable and RF cable Noun: SYV solid polyethylene insulation, PVC sheath, the national standard code is RF cable commonly known as "video cable";
SYWV polyethylene physical foam insulation, PVC jacket, the national standard code is radio frequency cable;
The same point:
1, the same characteristic impedance 75 ohms;
2, the outer sheath, shield structure, insulation outer diameter, braid selection, material selection, shielding layers, etc. are basically the same;
1, different physical characteristics of the insulation layer: SYV is 100% polyethylene filled, dielectric constant ε = 2.2-2.4 or so; and SYWV is also polyethylene filled, but filled with 80% of the nitrogen bubbles, polyethylene contains only 20%.
2, the core diameter is different: 75-5, for example, due to the -5 cable structure of the national standards, the outer diameter of the insulation layer is 4.8mm, can not be changed, in order to ensure that the characteristic impedance of 75Ω, and the characteristic impedance is only related to the internal and external diameter of the conductor than the insulation layer of the dielectric constant ε size, ε large core fine, ε is small core thick; core diameter: SYV is 0.75-0.8mm, SYWV is 1.0mm; (core wire structure form can be single or multi-stranded); this difference, resulting in a different core wire resistance.
3, the above two fundamental differences, determines the transmission characteristics of the two cable transmission attenuation is different, SYV cable is the earliest coaxial cable, in the decades has been using it to transmit, including transmission of radio frequency signals; but then when SYWV appeared, radio frequency above the band on the application of SYV is rare. Because the difference in high-frequency attenuation is too great; slowly SYV is basically mainly used to monitor the video transmission, people also put this RF cable "old man", commonly known as "video cable".
Measurement of 1000 meters of cable video transmission performance:
SYWV75-5/64 braided cable: 0.5M-5.15db; 6M-19.12db.
National standard high-quality SYV75-5/96 braided cable: 0.5M-6.43db, 6M-21.76db (the same braided structure cable attenuation than the foam cable 3db - that is, more than 1.4 times larger); there is a quite famous manufacturers products, SYV75-5/128 braided cable, 6M-25.22db, attenuation than the foam cable more than 6db - that is, more than two times larger);
Regarding high braided cables, it generally refers to cables with more than 96-128 braids. High braided cable is obviously characterized by: DC resistance of the shield is small, 200KHz below the low-frequency attenuation is reduced, to inhibit low-frequency interference is beneficial, the measurement shows that 200KHz-6MHz frequency, due to the "skin effect", 128 braided and 64 braided attenuation is the same.
Copper clad steel core wire: This is a kind of SYWV cable, used for cable TV more than 46MHz RF transmission, due to the "skin effect", the current flows only in the steel wire outside the copper skin, attenuation characteristics and the same pure copper core wire, tensile strength is much higher than the copper wire; but this cable can not be used for video transmission, 0-200KHz low-frequency attenuation is too large. 200KHz low-frequency attenuation is too large;
SYWV cable video and RF transmission characteristics are excellent, and because of the huge cable TV market support, production is very large, the price also has an advantage!