Technical parameters of RF coaxial cables
1、 Common coaxial cable types and performance:
1) SYV75-3, 5, 7, 9..., 75 ohms, polyethylene insulated solid coaxial cable. In recent years, some people have referred to it as a "video cable";   
2) SYWV75-3, 5, 7, 9... 75 ohms, physically foamed polyethylene insulated coaxial cable. Some people refer to it as a "radio frequency cable";   
3) Basic performance:
The physical structure of SYV is 100% polyethylene insulation; SYWV is a physically foamed polyethylene insulated cable with a foaming rate of 70-80%; Due to dielectric loss, the attenuation of SYV solid cables is significantly greater than that of SYWV physical foam cables; Among commonly used engineering cables, physical foam cables are still cables with good transmission performance but low price, and are used in various bands such as video, RF, and microwave. The test data provided by the manufacturer also illustrates this point;   
Coaxial cables can be used in DC, RF, and microwave bands. Distinguishing cables based on "radio frequency"/"video" not only lacks sufficient basis, but also easily leads to misleading: it seems that video transmission must or can only choose solid cables (choose those with high attenuation and high price?); From an engineering application perspective, it is more practical to distinguish types based on "solid core" and "foam" cables;
Differences in characteristics between high frequency (128) and low frequency (64) cables: Laboratory experimental studies have shown that in the frequency band below 200KHz, the "low resistance" of the shielding layer of high frequency cables plays a major role, so the low-frequency transmission attenuation is smaller than that of low frequency cables. However, in the video, radio frequency and microwave bands above 200-300KHz, as the "high-frequency skin effect" plays a major role, the high braided cable has lost the advantage of "low resistance", so the two types of high-frequency attenuation cables are basically the same.  
2、 Understand the video transmission characteristics of coaxial cables - "Attenuation frequency characteristics" Coaxial cable manufacturers generally only provide attenuation data for several RF points ranging from tens to hundreds of MHz, but have not yet provided detailed data and characteristics of the video frequency band; The laboratory conducted research and testing results on typical SYWV75-5 and 7/64 braided cables.

Basic characteristics of coaxial transmission characteristics:
1. The thinner the cable, the greater the attenuation: for example, the attenuation of a 75-7 cable at 1000 meters is roughly equivalent to the attenuation of a 75-5 cable at over 600 meters, or the transmission effect of a 75-7 cable at 1000 meters is roughly equivalent to that of a 75-5 cable at over 600 meters;
2. The longer the cable, the greater the attenuation: for example, the "decibel number" of 6M frequency attenuation for 75-5 cables at 750 meters is 75% of the "decibel number" of attenuation at 1000 meters, which is 15db; The attenuation at 2000 meters (1000+1000) is 20+20=40db, and the calculation method for other frequency points is the same. According to the test data of the 1000 meter cable above, when calculating the attenuation of cables of different lengths, please remember that "the decibel number is an alkali addition relationship" or "the attenuation decibel number can be calculated according to the percentage relationship of length change", which can be flexibly used;
3. Frequency distortion characteristics: reduced low-frequency attenuation and large high-frequency attenuation. The difference in attenuation between high and low edge frequencies can be called the "edge frequency difference", which is a very important parameter. The longer the cable, the greater the "edge frequency difference"; Fully understanding and mastering the "frequency distortion characteristics" of coaxial cables is of great significance in engineering; This is a key characteristic that affects image quality and is also a problem that is easily overlooked in engineering.
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