How to distinguish the quality of the video cable

Visual identification:

1. PVC sheath: The surface can see the regular "unevenness" of the knitting inside, indicating that the processing technology is good and there will be no relative sliding, which is a good cable. The appearance is smooth, and the "unevenness" of the compressed braid is not visible. The jacket is loose when it is pinched by hand, which is a poor cable;

2. Check the shield layer network: is the number enough? Copper braid, check solderability, tinned copper wire scrape to see if it is copper wire, the hardness of aluminum-magnesium alloy wire is significantly greater than copper wire; braided wire mesh is sparse, unevenly distributed, not tightly wrapped with insulating layer, etc. is poor cable;

3. Check the core wire: diameter-SYV cable is 0.78-0.8mm, SYWV cable is 1.0mm; recently a SYV75-5 core wire diameter is 1.0mm cable, the characteristic impedance of this cable is definitely not 75 Ohm, not applied to 75 ohm transmission system;

4. Check the adhesion force of the core wire and the insulation layer: cut the insulation layer obliquely and pull the core wire away in the stripping direction to see if the core wire and the insulation layer are bonded with process materials; good cables have a large adhesion force, poor The cable is not bonded;

5. Longitudinal tensile test: take one meter of cable, peel off the core wire in layers, insulation layer, shielding layer, outer house, and leave 10 cm long each. The method is: two hands hold the adjacent two layers of the cable and pull in the opposite direction; the good cable generally cannot be pulled by force, and the poor cable can be easily pulled out without effort-the elevator cable is very important, many so-called "Elevator special cables" have problems in this regard;

Transmission performance test:

Video cable, as the name suggests, is a transmission line used to transmit video signals. Since it is transmitting video signals, at least we must understand the transmission characteristics of the transmission line in the 0-6M frequency band, or rather, the transmission performance. Here we mainly talk about the "oscilloscope measurement method" for reference, because the oscilloscope is one of the necessary "weapons" for the engineering company and one of the necessary inspection equipment for qualification review; the following description is based on the ability to use the oscilloscope proficiently.

1. The color camera video signal can be used as a "standard video signal source": the video output of the camera used in the test project, the amplitude on a 75 ohm load should be 1Vp-p, that is, the bottom of the line sync head to the highest white level of the video signal "Peak-peak value"; note that the amplitude of the line sync head is "-0.3V" and the amplitude of the color burst head (4.43M sine wave pulse) is 0.3Vp-p; select the sensitivity of the oscilloscope and hit the amplitude calibration state. Select a camera with good index as the "video source";

2. The test cable should be as long as possible to reduce the measurement error. For example, 1000 meters, the middle connector of the cable must use the "F-type connector" and coaxial double-pass (cable TV equipment), do not use the welding method, because the welding method damages the cable Coaxiality and continuity of characteristic impedance.

3. Measure the DC resistance data of the cable: such as SYV75-5 cable 1000 meters, DC resistance core wire is 35-40 ohms, the outer shield layer resistance is 1000 meters is 24-36 ohms (different shielding layer number, the resistance varies greatly) ; SYWV75-5 cable 1000 meters, DC resistance core wire is 18-22 ohms, outer shielding layer resistance is 1000 meters is 24-36 ohms; it is useful to accumulate this information