Difference between SYV and SYWV Series Cables

SYWV's shielding performance is not as good as SYV's. SYV uses anti-oxidized copper as the shielding net, SYWV uses tinned copper as the shielding net, and tin-plated copper actually uses pure copper or copper scraps or even copper alone. Can not see it, only the manufacturer knows. This is one of the reasons why SYWV is not supported in monitoring systems. The video effect of the surveillance system imposes high requirements on the anti-interference ability of the shielded network. SYWV is generally used for radio frequency transmission signals, and there is no high monitoring system for anti-jamming capability requirements.

What are the main differences between video and RF lines?

[noun]:

SYV - solid polyethylene insulation, PVC jacket, the national standard code is RF cable - commonly known as "video cable"; SYWV - polyethylene physical foam insulation, PVC jacket, the national standard code is RF cable;

[Same point]:

1. The same characteristic impedance - 75 ohms;

2. The outer jacket, shielding layer structure, number selection, material selection, shielding layer number, insulation layer outer diameter, etc. are basically the same;

[difference]:

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; and SYWV is also filled with polyethylene, but it is filled with 80% of nitrogen bubbles, and the polyethylene content is only 20%. The average dielectric constant ε = 1.4 or so; ε = ε + j ε ", where ε" is the loss term, and the air ε" is basically "1". This process was accomplished in the 1990s and it effectively reduced the number of coaxial cables. Dielectric loss;

2. The diameter of the core wire is different: Take 75-5 as an example. Since the -5 cable structure standard stipulates that the outer diameter of the insulation layer (ie the inner diameter of the shielding layer) is 4.8mm, it cannot be changed. In order to guarantee the characteristic impedance of 75Ω, the characteristic impedance is only It is related to the diameter ratio of the inner and outer conductors and the dielectric constant ε of the insulating layer. The ε large core wire is fine, the ε small core wire is thick, the core wire diameter: SYV is 0.78-0.8mm, SYWV is 1.0mm; the core wire structure can be This is a single strand or multiple strands; this difference leads to a difference in core resistance. As measured Tiancheng, Aipu SYV75-5 cable, 1000 meters DC resistance 39Ω, typical SYWV75-5 cable, 1000 meters DC resistance 19-20Ω;

3. The above two fundamental differences determine the transmission characteristics of the two cables - transmission attenuation is different, SYV cable is the earliest coaxial cable, it has been used in tens of hundreds of years of transmission, including the transmission of radio frequency signals; but Later, when SYWV appeared, SYV was rarely applied to radio frequency bands. Because the high-frequency attenuation difference is too great; slowly SYV is basically used in surveillance video transmission, also called the "Veteran" of this radio frequency cable, renamed "video cable". But this is not equal to saying: SYV "video cable" video transmission characteristics better than SYWV, the actual situation is just the opposite, SYWV video transmission characteristics are also better than SYV cable. Misunderstandings in this area are common, and the misunderstandings in the South of our country are more serious than those in the North. We believe that the transmission of video signals must use video cables. Measured 1000 meters cable video transmission performance, 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 network structure cable attenuation is 3db larger than the foaming cable (that is, 1.4 times larger), there is a quite famous manufacturer's product, SYV75-5/128 braided cable, 6M-25.22db, attenuation is more than 6db more than the foaming cable — - that is, 2 times more;

4. With regard to high-alarm cables, generally referred to as 96-128 or more cables. High-profile cable is obviously characterized by: the DC resistance of the shielding layer is small, and the low-frequency attenuation below 200KHz is reduced, which is beneficial to the suppression of low-frequency interference. The actual measurement shows that the frequency of 200KHz-6MHz is similar to that of 128-series and 64-series attenuation due to the “skin effect”. (The high-frequency current flows only on the outer surface of the core and the inner surface layer of the shield flows). From the perspective of frequency distortion (high- and low-frequency attenuation differences), Gao Bian's cable is rather serious. The direct influence of frequency distortion is the normal ratio of various frequency components of the video signal, which directly affects the image distortion.

5. Copper clad steel core wire: This is a kind of SYWV cable, used for cable TV transmission above 46MHz. Due to the “skin effect”, current flows only in the copper skin outside the wire, attenuation characteristics and pure copper core Like the wire, the tensile strength is much higher than that of the copper wire, but this kind of cable is not suitable for video transmission, and the 0-200KHz low frequency attenuation is too large;

6. The SYWV cable video and RF transmission characteristics are excellent, and due to the huge support of the cable TV market, the output is very large and the price is also advantageous;

7. There are misunderstandings and misunderstandings about video and RF lines. The heated debate in the forum is an example. But everyone should respect the practice: use a 1000m 75-5 cable to transmit a color camera signal, send the end of the monitor to the monitor, monitor loop output to the oscilloscope, measure the amplitude of the "color burst head", the original signal is 0.3V For comparison, the longer the cable, the greater the difference between the two, the easier it is to compare;

supplement:

1. SYV solid cable used by the shielding material, structure, number, number of layers and other types, SYWV foam cable also has, do not be selected by the individual cable manufacturers or vendors, but some SYWV foam cable Only used for RF transmission structure, such as copper-clad steel core wire, aluminum foil shielding, aluminum-magnesium alloy braided wire (not solderable), SYV solid cables are rarely used;

2. Interference is not “drilled” into the gap in the braided network; it is a disturbance induced current, which generates an interference voltage (electromotive force) on the total resistance of the shield and forms a video signal through the matching resistor at both ends. Disturbing. The total resistance of the cable shield of the high-knit cable is smaller than that of the cable of the low-profile cable, and the induced electromotive force generated by the interference is also smaller, which is beneficial to suppressing interference. However, this is only a certain degree of weakening, and it cannot be considered as a cable of the high-profile series. Anti-interference cable."