These security monitoring line knowledge

Transmission performance test: Video cable, as the name implies, is used to transmit video signal transmission lines. Because it is to transmit video signals, at least we must understand the transmission characteristics of transmission lines in 0-6 meters, transmission performance. Here mainly to talk about "oscilloscope measurement method", a total quote, because the oscilloscope is the necessary "weapons" for the project, qualification examination will detect equipment; the second narrative is based on the ability to use the oscilloscope on the basis of proficiency.

1, camera video signal can be used as a color "standard video signal source": test engineers to complete the video output of the camera, in the 75 ohm negative monitoring line load range should be 1Vp-p, that is, the highest video signal at the bottom of the line synchronization header White level "peak-peak"; note that the head is synchronized "0.3V", color sync head (4.43 meters sinusoidal pulse) rate is 0.3Vp-p; select the oscilloscope sensitivity, hit rate calibration status. Choose a better camera measurement indicator as "video source";

2. It takes a long cable to test as far as possible to reduce the measurement error, such as 1000 meters, in the cable connector must use "F-joint" and coaxial two-way (cable television equipment), do not use the welding The method, because of the way to break the continuity of the coaxiality of the welding and the characteristic impedance.

3, DC resistance measurement cable data: such as SYV75-5 cable 1000 meters, DC resistance for 35-40 ohms, the outer shield resistance table is 100024-36 ohms (the shielding layer composition is different, the resistance is very different); SYWV75- 5 cable 1000 meters, DC resistance is suitable for Hsinchu ohm, outer shield layer resistance meter is 100024-36 ohms; this information accumulates useful monitoring line, not only can judge the quality of cable material, but also used for engineering wiring, wear quality inspection, such as ancient people Pipes and lines are broken, resistance changes, video signals are weak, and there are erroneous interferences. The chance of this “accident” is high, but they are often overlooked;

4、Measurement and monitoring of the high-frequency attenuation characteristics of the cable: After measuring the gear and the color repetitive head repeatedly, the 0.3V is 0 dB benchmark, the calculated amount of attenuation represents the low-frequency attenuation repeated lines, the color represents 4.43 meters high, and the head attenuation frequency is synchronized. , For example: 1000MiHang synchronization head is 0.15V, according to the logging calculation of more than 20 for the decibel attenuation "6dB / 1000M", 4.43M color synchronization head 1000 meters after the attenuation rate is 30mv, that is, the first time, attenuation for-20db /1000 meters; This method can accurately grasp the quality of different transmission cables and use "high-frequency distortion (high-frequency attenuation)" intuitive concept, you can more accurately measure the same type and structure of SYV and SYWV cables Differences and performance are good. Compare different manufacturers' product differentiation and performance, good or bad, you can also compare different batches of products from the same manufacturer and replace them.

5, the above method can also detect the performance of video transmission systems and equipment: such as engineering coaxial cable transmission characteristics of each channel of optical fiber transmission characteristics (can be measured is good or bad, do not think it is so ideal), RF transmission, microwave Transmission characteristics, transmission characteristics of the twisted pair, distribution characteristics of the video distributor, master switch characteristics of the matrix, we must pay particular attention to when the output of many channels and the input signal switching are also the same, if it is found that more exchange his attenuation, wrong , It should be a constant. After the motion, you will master many unqualified products;

6. Observe the on-site signal, see a large distortion of the sync position (flat) - should be very flat; at the same time, it can seem to interfere with the oscilloscope at low frequencies: such as signal and slow fluctuations, 50/100-period interference, there are many The "protection" of the beat, the main harmonic frequency interference, remote camera disconnection, cable conductor internal and external short-circuit remote, and finally with the oscilloscope can directly observe the interference waveform and power, this method can also check and test the device real anti-jamming performance.