SYWV material video cable (1)

Update:Dec 08,2021
Summary:SYWVsywv refers to the coaxial cable with polyethylene physical foam insulation, the national standard code is radio frequency cableSame point1. The c...
sywv refers to the coaxial cable with polyethylene physical foam insulation, the national standard code is radio frequency cable
Same point
1. The characteristic impedance is the same-75 ohms;
2. The outer sheath, shielding layer structure, insulating layer outer diameter, number selection, material selection, shielding layer number, etc. are basically the same.
1. The physical properties of the insulating layer are different: syv is filled with 100% polyethylene, and the dielectric constant ε=2.2-2.4; while sywv is also filled with polyethylene, but filled with 80% nitrogen bubbles, polyethylene only contains 20%, macroscopic The average dielectric constant ε=1.4; ε=εǎ?jε", where ε" is the loss term, and the ε" of air is basically "0". This process was achieved in the 1990s and it effectively reduced the coaxial cable’s Dielectric loss;
2. The diameter of the core wire is different: Take 75-5 as an example. Due to the specification of the -5 cable structure, the outer diameter of the insulation layer (ie the inner diameter of the shielding layer) is 4.8mm, which cannot be changed. In order to ensure the characteristic impedance of 75 ohms, the characteristic impedance It is only related to the ratio of the inner and outer conductor diameters and the dielectric constant ε of the insulating layer. Large ε core wire is thin, ε small core wire is thick, core wire diameter: syv is 0.78-0.8mm, sywv is 1.0mm; core wire structure forms are both It can be single strand or multiple strands; this difference results in a difference in core wire resistance. According to the actual measurement of Tiancheng and Aipu syv75-5 cable, the DC resistance of 1000m core wire is 39Ω, the typical sywv75-5 cable, the DC resistance of 1000m core wire is 19-20Ω;
3. The above two fundamental differences determine the transmission characteristics of the two cables-the transmission attenuation is different. The syv cable is the earliest coaxial cable. It has been used for transmission for dozens of hundreds of years, including the transmission of radio frequency signals; but Later, when sywv appeared, syv was rarely used in bands above radio frequency. Because the difference in high-frequency attenuation is too large; the slow syv is basically mainly used for surveillance video transmission, so the "old man" of this kind of radio frequency cable is renamed "video cable". But this is not the same as saying: the video transmission characteristics of syv "video cable" are better than sywv. In fact, it is just the opposite. The video transmission characteristics of sywv are also better than syv cables. Misunderstandings in this area are common, and the misunderstandings in the south of our country are more serious than those in the north. They believe that to transmit video signals, "video cables must be used." Measured the video transmission performance of 1000m cable, sywv75-5/64 series cable: 0.5m—5.15db, 6m—19.12db; national standard high quality syv75-5/96 series cable: 0.5m—6.43db, 6m—21.76db (same series The attenuation of the net structure cable is 3db larger than that of the foamed cable—that is, more than 1.4 times). There is a quite famous manufacturer's product, the syv75-5/128 braided cable, 6m-25.22db, and the attenuation is 6db larger than that of the foamed cable— -That is more than 2 times larger);