Dec 06, 2019 23:00:00

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

A single board computer `` Raspberry Pi 4 '' that was released overseas in June 2019 and passed the

technical standard conformity certification (technical suit) from November 2019 and sold in Japan has a specific screen output If you set the 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 2560x1440 screen resolution
https://www.enricozini.org/blog/2019/himblick/raspberry-pi-4-loses-wifi-at-2560x1440-screen-resolution/

This is the Raspberry Pi 4 purchased.

The problem this time is that 'If you set the screen output to 2560x1440 resolution with Raspberry Pi 4, it may be difficult to connect to

2.4GHz Wi-Fi .' Start verification by connecting Raspberry Pi 4 to a 4K monitor.

For the 2.4GHz band Wi-Fi connection source, we used the '

Pocket WiFi 504HW ' mobile router.

The resolution of the screen output from Raspberry Pi 4 was set to 3840x2160 in the initial state.

When the resolution is 3840x2160, the connection to Wi-Fi was confirmed.

Next, set the screen output to “2560x1440”. Since the target resolution was not displayed in the resolution selection menu, enter the following command.

sudo xrandr --newmode '2560x1440' 146.25 2560 2680 2944 3328 1440 1443 1448 1468 -hsync + vsync
sudo xrandr --addmode HDMI-1 '2560x1440'

When executed, the item “2560x1440” 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 2560x1440, 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. Try using the spectrum analyzer

Wi-Spy to see if radio waves are actually emitted.

With this feeling, check Wi-Spy close to HDMI.

In the graph, the vertical axis is the strength of the radio wave, the horizontal axis is the frequency, the orange line is the area of the channel to which the mobile router's radio wave corresponds, and the stronger the color, the stronger the radio wave is emitted . At 3840x2160 resolution, the channel area of the mobile router is not particularly responsive.

Next, when I set the resolution to 2560x1440, 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.

A similar problem has been reported in the official forum of Raspberry Pi, and there is a possibility that a patch will take action.