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What are the causes of cable interference?

Update:11-01-2021
Summary:

It is well known that the cable is the most critical el […]

It is well known that the cable is the most critical element that causes the electromagnetic compatibility test problem in the system. And many people will ask what to do if the cable suffers interference? Today, the web editor will come to find out.
The problem of cable radiation source
The problem of cable radiation source is one of the most common problems in engineering projects. About 90% of machinery and equipment cannot be tested according to the emission point of the radiation source because of the cable radiation source.
There are two principles of radiation sources caused by cables, one is the differential mode radiation source caused by the data signal current control loop in the cable, and the other is caused by the common mode current on the transmission line in the cable.
The key source of cable radiation comes from the common mode radiation source. The common-mode radiation source is caused by the common-mode current. The total loop area of ​​the common-mode current is generated by the cable and the ground, so it has a large total loop area, which will cause a strong radiation source.
Increase the impedance of the common mode current control loop
After the machine equipment is assembled, the common mode operating voltage caused by the machine equipment cable will be fixed. At this time, the way to reduce the common mode current on the cable is to increase the impedance of the common mode current control loop. However, how to increase the impedance of the common-mode control loop is a problem that many technical engineers wonder. They usually try to increase the impedance of the common-mode control loop by breaking the connection between the circuit board and the main box, or between the main box and the safety ground. The result is usually chilling.

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