For the identification of the quality of the cable, the real detection requires special equipment and instruments. In actual engineering, the preliminary identification can be carried out according to the following methods:

1. Check the braiding of the shielding layer: whether the number of braids is enough, copper braided, check the solderability, scrape the tinned copper wire to see if there is copper wire inside, the hardness of the aluminum-magnesium alloy wire is obviously greater than that of the copper wire; the braiding is sparse, Uneven distribution, not tightly wrapped with the insulating layer, etc. are poor cables.

2. PVC sheath: The surface can see the regular "unevenness" of the woven net inside the compressed net, indicating that the processing technology is good, there will be no relative sliding, and it is a good cable; the appearance is smooth, and the "unevenness" of the compressed net can not be seen. Unevenness", there is a loose feeling when the sheath is pinched by hand, which is a poor cable.

3. Check the adhesion between the core wire and the insulating layer: cut the insulating layer diagonally, pull the core wire in the peeling direction, and see if the core wire and the insulating layer have bonding process materials; good cables have greater adhesion, poor cables. Not glued. Longitudinal tensile test: Take one meter of cable, peel off the core wire, insulation layer, shielding layer and outer sheath, each with a length of 10 cm. The method is: hold the adjacent two layers of the cable with two hands and pull them in opposite directions; good cables cannot be pulled with general force, and poor cables can be easily pulled out without much effort.

4. Check the core wire: diameter - SYV cable is 0.78 to 0.8mm, SYWV cable is 1.0mm; recently there has been a SYV75-5 cable with a core wire diameter of 1.0mm, the characteristic impedance of this cable is definitely not 75 Ohm, do not apply to 75 Ohm transmission system.