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What is the main difference between video cable and RF cable

Date:2012-11-20  Hits:3931

 What is the main difference between video cable and RF cable
SYV: solid polyethylene insulation, PVC jacket, GB Code RF cables - also known as "video cable";

SYWV: polyethylene physics of foam insulation, PVC jacket, GB code RF cable;

Same point]:

Characteristic impedance: 75 ohms;

Substantially the same outer sheath, the structure of the shielding layer, the outer diameter of the insulating layer, the Programme number selection, the choice of material, shielding layers;

[Difference]:

Different physical characteristics of the insulating layer: SYV 100% polyethylene fill, permittivity ε = 2.2-2.4; SYWV also polyethylene filled, but charging 80% of nitrogen bubbles, polyethylene contains only 20%, the macroscopic average dielectric the dielectric constant ε = 1.4; ε = ε + jε ", where, ε" is the loss term, the air ε "substantially" 0 ", technological achievements in the 1990s, it effectively reduces the dielectric of the coaxial cable loss; - The first difference is ε of different sizes, the different attenuation of the insulating medium;

Different from the diameter of the core wire: 75-5, for example, -5 cable structure standard requirements, the outer diameter of the insulating layer (i.e., shielding the inner diameter) is 4.8mm, can not be changed in order to ensure a 75Ω characteristic impedance, and the characteristic impedance of the inner and outer related to the size of the conductor diameter ratio and the dielectric constant ε of the insulating layer, the fine line ε large core crude ε small core wire, the core wire diameter: SYV is 0.78-0.8mm, SYWV is 1.0mm; the structural form of the core wire may be a single more strands; This distinction has led different core wire resistance. As measured Tiancheng, EUP SYV75-5 cable, 1000 meters of core wire DC resistance of 39Ω typical SYWV75-5 cable, 1000 meters of core wire DC resistance of 19-20Ω, poor doubled;

These two fundamental difference between the two cable transmission characteristics - transmission attenuation, varying degrees of frequency distortion. Measured 1000 m cable video transmission performance the SYWV75-5/64 compiled cable: 0.5M-5.15db 6M-19.12db; GB qualified SYV75-5/96 knitting cables: 0.5M-6.43db, 6M-21.76db (the same compiled network structure cable attenuation than foam cable 3db - that is more than 1.4 times larger), there is a pretty well-known manufacturers products, the SYV75-5/128 compiled cable, 6M 25.22db, attenuation than the foam cable above 6db - - that is more than 2 times larger);

High editing cable, generally refers to the cable over 96-128 knitting. High knitting cable significantly characterized by: the DC resistance of the shielding layer is small, 200KHz below the low-frequency attenuation, advantageous for suppressing low-frequency interference, the test shows, 200KHz-6MHz frequency, due to the "skin effect", the 128 series and the attenuation of the 64 knitting. (High-frequency current flows only in the outer surface of the core wire and the inner surface of the shield layer flow). Frequency distortion (high and low frequency attenuation differences), high Editing cable instead. The frequency the distortion directly affect the normal proportion of the various frequency components of the video signal distortion, directly affect the image distortion;

Copper clad steel core wire: This is a kind of SYWV cable for CATV RF transmission of more than 46MHz, due to the "skin effect", current flows only in the outside of the copper wire, the attenuation characteristics and pure copper wire tensile strength but is much higher than copper; However, this cable does not work for video transmission ,0-200KHz low frequency attenuation is too large;

RF transmission characteristics of SYWV Cable video are excellent, and the huge cable TV market support, production, price advantage;

Video cable and RF line, both misunderstood and misleading, evidenced by a fierce debate in the Forum. But everyone should respect the practice: 1000 m 75-5 cable to transmit the signal of a color camera, end gave Monitors, monitor loop output to an oscilloscope, the magnitude of the measured burst head ", the original signal is 0.3V , for comparison, the longer the cable, the two bigger the difference, the more easily compare.