Today we will continue to discuss the theoretical model and rectification methods of radiation launch rectification, and explain in depth that theory and practice complement each other. In the RE102 test, an iron shell product has a single point exceeding 200 meters in the frequency range of 200MHz~1GHz, and the high frequency has a high stray point. In the face of this situation, how can we rectify it? Before the opening, we first put a model, the current in the conductor and the reflow will be a different frequency distribution, please see the following figure: From the above figure, we can see that the low frequency runs all over the ground, so if we need to shield, we should shield a wide area and cover the reflow area. The high frequency reflow area is very small, so the area to be controlled is very small. . Imagine if a long ground wire is drawn in the high-frequency reflow (GND or VDD) plane, and the PCB plane is not effective enough to shield the lead wire, so that the lead has high radiation efficiency. For low frequencies, why do you need to ground at a single point? There are many reasons for this. To control the return path itself, you must also prevent digital noise from invading through the ground common impedance and affect performance. ã€Symptom】 In this project, in the RE102 test, more than 200 MHz single point in the frequency band 200MHz~1GHz exceeded the standard, and the high frequency has a high stray single point. The data is shown in the following figure: ã€Cause Analysis】 Quick positioning: The product is an iron shell product. Many cables are pulled out in the laboratory. The cables are plugged one by one. It is found that the interference comes from the DVI cable. The DVI cable is buckled and the interface is grounded and shielded. The low frequency of more than 200 MHz went down, the middle of the up, and exceeded the standard, this is why, please see the following picture: In-depth study: From the above measures, we can see that whenever we grounded, no matter how close, there will be different but similar frequency points are beyond the standard, and it has little to do with the magnetic ring, no matter whether it is added or not. There are indications that we have other sources of noise that have not been found, so we disassemble the machine and specifically study whether the cable is grounded. We finally found the reason. The external shield of the cable at the grounding point appears in the machine. The place is isolated with a plastic stopper. Remove the plug or put on the conductive cloth, RE radiation is immediately OK, please see the picture below: ã€Rectification program】 The waterproof product of the integrated product, the plug can not be removed, so the plug should be made into a conductive plastic plug. This program does not need to be revised, only need to change the plastic plug material, and has no effect on other performance. Just say two sentences The model of the plug is like a PCB, and a large gap is opened in the return path. The plug is filled or the PCB crack is filled and the flow is continuous. In addition, we can also consider the phase problem of the antenna here. The two points are connected together, the potential phase is the same, there is no power line, so there is no electromagnetic field, of course, there is no electromagnetic wave. Shenzhen ChengRong Technology Co.,Ltd. , https://www.dglaptopstandsupplier.com
