The difference between electromagnetic interference and jammers
Influence of electromagnetic interference on equipment work
There are three representative sets of data describing the impact of power line interference on the operation of wifi jammer equipment, which were made by IBM, AT & T and the US Navy:
① Allen and Segal of IBM in the United States made statistics and analysis of the failure of 49 computers installed in the United States, Canada and Mexico in 1974. 39.5 [%] is pulse interference, 11 [%] is voltage drop, and another 0.5 [%] is power interruption.
② Goldstenin and Sperenza of American AT & T Company analyzed the causes of communication equipment failure in 1982, and considered that among the causes caused by the power supply, 87 [%] is voltage drop, 7.5 [%] is pulse interference, and 4.7 [%] It is a power failure, and another 0.8 [%] is a voltage surge.
③ The US Navy ’s Thomas Key summarized the computer accidents of the navy system within ten years, and believed that the low voltage was the primary cause of computer failure.
The conclusions of the above three sets of data are quite different, and the difference can be attributed to the difference of statistical objects. However, some clues can still be seen from the three sets of data: there are two main reasons for equipment failure due to power supply problems, namely, low voltage and transient interference (oscillation transients and pulse interference) in the power supply, but these and interference There is a qualitative difference in device interference.
Method for shielding electromagnetic interference
EMC problems are often a reason for restricting the export of Chinese electronic products. This article mainly discusses the sources of EMI and some very specific suppression methods.
Electromagnetic compatibility (EMC) refers to "the performance of a device, device or system that can make it work in its own environment and at the same time will not cause strong electromagnetic interference to any other equipment in this environment (IEEE C63.12 1987) "For wireless transceiver equipment, the use of non-contiguous spectrum can partially achieve EMC performance, but many related examples also show that EMC is not always able to achieve such There are high-frequency portable jammer between cell phones and medical instruments, and we call this interference electromagnetic interference (EMI).
All electrical and electronic equipment will have intermittent or continuous voltage and current changes during operation. Sometimes the rate of change is still quite fast. This will cause electromagnetic energy to be generated in different frequencies or between a frequency band, and the corresponding circuit will emit this energy. Into the surrounding environment.
There are two ways for EMI to leave or enter a circuit: radiated and conducted signal radiation leaks out through slots, slots, openings, or other gaps in the housing; while signal conduction leaves the housing through coupling to power, signal, and control lines Free radiation in an open space creates interference, but this interference is different from the band emitted by the jammer.
A lot of EMI suppression is achieved by a combination of shell shielding and slot shielding. In most cases, the following simple principles can help to achieve EMI shielding: reduce interference from the source; isolate and enhance the circuit of interference by shielding, filtering or grounding The EMI suppression, isolation and low sensitivity of the anti-jamming capability of sensitive circuits should be the goals of all circuit designers, and these performances should be completed early in the design stage.
For design engineers, the use of shielding materials is an effective way to reduce EMI. Nowadays, a variety of shell shielding materials are widely used, from metal cans, thin metal sheets and foil tapes to spray coating on conductive fabrics or tapes And the coating (such as conductive paint and zinc wire spraying, etc.) whether it is metal or plastic coated with a conductive layer, once the designer determines that it is used as the shell material, you can start to choose the gasket.