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5 points about RF connector signal interference solution

Author: Date:4/18/2019 1:09:19 AM
  When the RF connector has a signal interference problem or cannot pass the test. The following five points of solution are summarized for your reference.


1) Although the chassis or cabinet is well shielded, the radiated emissions are too high or cannot pass the radiated immunity test. This is because the outer tow cable on the chassis or cabinet acts as an antenna. One characteristic of an antenna is reciprocity, that is to say: if an antenna has high radiation efficiency, its receiving efficiency is also high. Therefore, the external tow cable of the device can generate strong radiation, and can effectively receive the space electromagnetic wave and pass it into the device to form interference to the circuit. For some reason, an interference current is formed on the outer towing cable, which conducts from the inside of the chassis and radiates electromagnetic waves using the cable as a radiating antenna. The solution to this problem is to install a filter at the port of the cable to filter out the interference current.


2) The independent equipment does not have any electromagnetic interference problem (radiation emission and immunity are fully qualified), but when connecting the necessary external cable, there is interference problem; this problem is the same as the first type of problem, that is, external drag The cable is equivalent to an antenna. When there is no cable, it is equivalent to no radiation antenna and receiving antenna, so it is easy to pass the radiation emission and immunity test, but when the cable is dragged, these cables act as radiation antennas and receiving antennas, resulting in enhanced radiation and space for the equipment. The sensitivity of the interference is increased. The solution is to install a filter at the port of the cable, and the electromagnetic energy received from the space from the space is filtered out before they reach the electronic circuit. On the other hand, the interference energy in the electronic circuit is prevented from entering the conductor and then radiated by the conductor. .


3) When an electrical fast pulse is injected on the signal cable, the fault occurs. We know that the frequency of the electrical fast pulse is very high. These interferences are coupled into the cable through the capacitive coupling clamp to form an interference current on the cable. These currents flow directly on the one hand. Into the circuit, the formation of interference to the circuit, on the other hand, radiation, forming interference to the circuit. The solution is to use shielded cables and add filters.


4) The electrical fast transient burst immunity test cannot be tested by the conduction sensitivity on the cable bundle to verify the immunity to transient disturbances caused by lightning, ground faults or switching inductive loads. This test is a burst test consisting of many fast transient pulses coupled to a power line, control line, or signal line, which can naturally be resolved by filtering at the cable port.


5) The effect of electrostatic discharge on the equipment circuit that cannot be tested by electrostatic discharge is largely due to the high-frequency electromagnetic field around the electrostatic discharge current. These electromagnetic fields are easily received by the wires due to their high frequency, which interferes with the circuit. When a device was subjected to an electrostatic discharge test, it was found that the circuit failed when discharging on the movable panel. Upon inspection, it was found that behind the panel was a bundle of cables, and the electromagnetic field generated by the electrostatic discharge current on the panel induced noise current on the cable bundle to form interference. The problem is solved after installing the filter at the port of the cable.


With the widespread use of switching power supplies, it is already necessary to install filters at the entrance of the power line. Because the switching power supply operates in a high power pulse state, it produces very strong electromagnetic radiation that induces a conductive emission on the line. If the filter is not used, it is impossible to pass the EMC test. In the design, the interference filter is often divided into two types: power line interference filter and signal line interference filter. From the circuit point of view, these two types of filters are the same, are low-pass filters, the reason for this division, mainly because the two have the greatest inhibition of electromagnetic interference, there are some Special considerations. The signal filter also considers that the filter does not have a serious effect on the working signal and cannot cause distortion of the signal. In addition to ensuring that the power supply filter is required to meet safety requirements, it is also important to note that when the load current is large, the inductance in the circuit cannot be saturated (resulting in a drop in filter performance).