Electromagnetic interference (EMI) reduces radio range, drastically decreasing the functionality of Internet of Things products. There are some local and intermittent EMIs that are eventually get addressed, thanks to the Wi-Fi protocols that come complete with automatic retry features. However, the interference coming from external sources are continuous in nature and can drastically reduce the range of a device’s onboard radio. This kind of interference has to be addressed by the right mechanical and PCB design. But what about the interferences that come right from your own product? Here are some useful tips that will help you minimize the EMI being emitted by your product and improve radio range:
Metal shields isolate circuits and prevent interference from reaching the antenna. At the same time, the antenna needs to be present outside the shield for receiving signals. So, shielding the interference sources is a better option than shielding the receiver. The Faraday cage is the best shielding solution available that provides a conductive box without any seams around the shielded circuitry.
However, you must develop metal shields with minimal contact resistance. And, there are several options to achieve this:
- Pick clear chromate instead of aluminum as it provides decent conductivity while resisting corrosion.
- Use an overlapping structure for an increased area and decreased contact resistance.
- Minimize contact resistance through gaskets that rely on screws outside the gasket for more reliable contact and compression force.
Select the Right Clock Frequencies
Certain circuits are never switched off, and the resulting interference affects the receiver’s sensitivity. In a controller board, for example, clock oscillator signal harmonics cannot be controlled easily and lead to interference. There is one clock of 19.2 MHz and another of 25 MHz in a Raspberry Pi design. While the latter falls between the popular non-overlapping Wi-Fi frequencies, the former falls inside the Wi-Fi frequency channels. So, even though the 25 MHz clock doesn’t solve the interference issue entirely, it does help to a certain extent.
Check for EMI Issues
Detecting interference issues becomes easier with a spectrum analyzer. Select one that has greater maximum frequency than the system radio’s highest frequency. When an antenna probe is connected to this analyzer, it can detect design problems and locate interference sources. No wonder this setup is used by the FCC to test for EMI compliance and radio performance issues.
Switching up the components of a PCB can work wonders when it comes to decreasing EMI interference and improving radio range. Sure, it’s better if you detect all the problems as early as possible, but it’s worth noting that following the steps above can result in a design that minimizes EMI emission and prevents interference from affecting other parts of the radio system. To know more about EMI shielding, click here.
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