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I actually verified the problem of “ Wi-Fi becomes unstable at a specific resolution '' of Raspberry Pi 4


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I actually verified the problem of “ Wi-Fi becomes unstable at a specific resolution '' of Raspberry Pi 4

Released overseas in June 2019, from November 2019Technical standard conformity certification (technical suit)Single board computer that has been sold in JapanRaspberry Pi 4"If you set the screen output to a specific resolution, Wi-Fi is difficult to connect. I actually tested to see what kind of problem occurred.

Raspberry Pi 4 Wi-Fi problem: Firmware update will fix your screen resolution bug | ZDNet
https://www.zdnet.com/article/raspberry-pi-4-wi-fi-problem-firmware-update-will-fix-your-screen-resolution-bug/

Raspberry Pi 4 WiFi stops working at 2560×1440 screen resolution
https://www.enricozini.org/blog/2019/himblick/raspberry-pi-4-loses-wifi-at-2560×1440-screen-resolution/

This is the Raspberry Pi 4 purchased.

The problem this time is "If you set the screen output to 2560×1440 resolution on Raspberry Pi 4,2.4GHz Wi-FiMay be difficult to connect toThat means. Start verification by connecting Raspberry Pi 4 to a 4K monitor.

For the 2.4 GHz band Wi-Fi connection source,Pocket WiFi 504HWWas used.

The resolution of the screen output from Raspberry Pi 4 was set to 3840×2160 in the initial state.

When the resolution is 3840×2160, the connection to Wi-Fi was confirmed.

Next, set the screen output to “2560×1440”. Since the target resolution was not displayed in the resolution selection menu, enter the following command.

sudo xrandr –newmode "2560×1440" 146.25 2560 2680 2944 3328 1440 1443 1448 1468 -hsync + vsync
sudo xrandr –addmode HDMI-1 "2560×1440"

When executed, the item “2560×1440” appears in the menu for changing the resolution, so change the resolution.

When I checked the Wi-Fi connection status, I was unable to establish a connection and was in an unstable state.

The problem this time is that if you set the resolution of the screen output from Raspberry Pi 4 to 2560×1440, radio waves close to 2.4 GHz band will be emitted from Raspberry Pi 4, so it will interfere with Wi-Fi in 2.4 GHz band about. Spectrum analyzerWi-SpyUse to check whether the radio wave is actually emitted.

Check with Wi-Spy close to HDMI like this.

In the graph, the vertical axis is frequency, the horizontal axis is Wi-Fi channel, the orange line is the area of ​​the channel to which the mobile router's radio wave corresponds, and the stronger the color becomes, the stronger the radio wave is emitted The At 3840×2160 resolution, the channel area of ​​the mobile router is not particularly responsive.

Next, when I set the resolution to 2560×1440, there was a response on the screen. Strong radio waves are generated in the channel area of ​​the mobile router, and it has been confirmed that there is a high possibility that the radio waves generated from the Raspberry Pi 4 and Wi-Fi are interfering.


Raspberry Pi official forumHowever, similar problems have been reported and may be addressed by patches.

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