Design your CM4 carrier with WiFi performance in mind

Raspberry Pi Compute Module 4 has a built-in WiFi antenna, but that doesn’t mean it will work well for you – the physical features of the carrier board also affect the quality of your signal. [Avian] Decided to do a simple test – change WiFi RSSI with a few different carrier boards and measure throughput. It appears that the carrier he used was owned, however [Avian] CM4 provides a sketch of how it stands on these.

The CM4 has two recommendations for making WiFi work better – placing the module’s WiFi antenna at the end of your carrier PCB and adding a certain size ground cutout below the antenna. [Avian] Tested with a total of three configurations – CMIO4 Official Career Board that complies with both of these rules, Career Board A which does not comply with either, and Career Board B which appears to be a copy of Board A with a ground cutout added.

WiFi RSSI graph plotting for each of the three carriers in each of the six locations.  CMIO4 consistently surpasses both, while Carrier B surpasses Carrier A, but at a much narrower interval.After setting up some test locations and writing a few scripts to facilitate testing, [Avian] Recorded test data. After plotting that data, it would seem that the presence of an under-antenna cutout helps, it does not affect RSSI as much as module placement. Of course, there are other variables that can affect RSSI results for your own design – fortunately, scripts used for logging are available, so you can test your own setups if necessary.

If you’re lucky enough to be able to design with a CM4 in mind and an external antenna isn’t an option for you, it can help you get a little more out of your WiFi antenna. [Avian]Every time this kind of thing is tested – a month ago, his ESP8266 GPIO 5V compatibility study led us to a heated discussion on the subject again. If WiFi is important to you, it’s understandable to stick to the design guidelines – after all, even the HDMI interface in Raspberry Pi can create its own WiFi radio error.

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