Using 5 GHz USB WiFi adapter

It is known that the power consumption of the Raspberry Pi 3 Model B+ and the Raspberry Pi 4 Model B can be problematic. This is especially the case if you are using a “wireless-internet to wireless-clients” connection, which involves the wireless chip on the board and an additional USB WiFi adapter. As a rule, simpler, low-powered USB WiFi adapters lead to fewer problems, meaning that this kind of USB WiFi adapters usually supports only 2,4 GHz and not 5 GHz networks. Since TorBox version 0.2.5, the Internet can also be accessed via the onboard WiFi chip, so that 5 GHz networks can be tapped. However, since the USB WiFi adapter might be missing on reboot, and a user might be locked out, TorBox will reset itself after a reboot, so that the onboard WiFi chip will again act as an access point and can be accessed with a SSH client. So there are good reasons to use a USB WiFi adapter that can access 5 GHz networks even after a reboot.

In this article, we want to investigate whether the use of 5 GHz USB Wifi adapters makes sense in terms of power consumption and what problems might be associated with it. We want to focus especially on the nano-sized adapters because they usually have a lower power consumption. Nevertheless, as an alternative, we tested a modern adapter, which is relatively large and has two antennas. The tests are performed exclusively on a Raspberry Pi 4 Model B because firmware updates in late autumn 2019 reduced its overall power consumption. Therefore, we assume that the Raspberry Pi 4 is in a better position than the Raspberry Pi 3 Model B+, which to our knowledge, has not experienced any such improvement. The following adapters were (by chance) available for the test (more adapters may be tested on request – let me know):

The Netgear AC1200

The Netgear AC1200is not supported “out of the box” by Raspberry Pi. It needs do have installed a driver for Realtek RTL8812BU. Fortunately, Fars Robotics provides such a driver for a variety of kernel versions.

To install the right driver, first, the version of the used Linux kernel has to be identified with the command uname -a. With the kernel version known (for example, 5.4.51-v71+ #1327), the correct driver package can be found here: http://downloads.fars-robotics.net/wifi-drivers/8822bu-drivers/. In our example, the driver package name is 8822bu-5.4.51-v71-1327.tar.gz. The next step is to download and install the driver before the first use of the Netgear AC1200:

# The * has to be replaced by the correct kernel version
cd ~
wget http://downloads.fars-robotics.net/wifi-drivers/8822bu-drivers/8822bu-*.tar.gz
tar xzf 8822bu-*.tar.gz
./install.sh 
The "hothead" Netgear AC1200
The “hothead” Netgear AC1200

After the driver’s installation and a reboot, the Netgear AC 12000 adapter is discovered by the Raspberry Pi and ready to use. In the TorBox main menu using entry 5, we get into the network manager (wicd) and see now all available 2,4 GHz and 5 GHz networks. When we connect with one of these networks, the adapter needs an unusually long time to authenticate itself with the chosen wireless network, however, it worked reliably every time. In contrast, during the tests, we would have to reset the network manager again and again (in the update and reset sub-menu, entry 7) because wicd crashed during configuration. Besides, the adapter in our tests lost the connection to the Internet after a few hours. In the time available, we could not determine whether this behavior was caused by too much power consumption, too much heat accumulation at the USB interface or the adapter, or whether the driver software was causing problems (rather unlikely). However, we noticed that the USB interface of the Raspberry Pi and the adapter itself heat a lot during operation, which is why we think it is primarily a thermal problem. These observations were made when using 2.4 GHz and 5 GHz networks as well as mains and battery operation. Despite this inconvenience, the adapter worked both at 2.4 GHz and 5 GHz networks. However, you can forget about any speed advantages. In our case, the network performance on the 5 GHz network was not higher than compared to a simple 2,4 GHz USB WiFi adapters.

The TP-Link Archer T2U Nano AC600

The TP-Link Archer T2U Nano AC600 does not work “out of the box” either – it needs a driver for the Realtek RTL8812au. Although Fars Robotics provides such a driver, currently, it is only available for the Linux kernel version 4.19.19 or older. In other words: with that adapter, we have to find another way to get it working. Fortunately, the project Aircrack-NG provides us with a solution:

# This should work with the latest kernel used by the Raspberry Pi OS, but probably not with older ones if the kernel headers are missing
cd ~
sudo apt-get -y install git dkms raspberrypi-kernel-headers
git clone https://github.com/aircrack-ng/rtl8812au.git
cd rtl8812au
sudo ./dkms-install.sh
The TP-Link Archer T2U Nano AC600
The TP-Link Archer T2U Nano AC600

After the successful installation of the driver, and a reboot, the TP-Link Archer T2U Nano AC600 adapter is discovered by the Raspberry Pi and ready to use. Like the Netgear AC1200, the TP-Link Archer T2U Nano AC600 takes an unusually long time to authenticate itself with a chosen wireless network. However, in contrast to the Netgear AC1200, there were no network manager crashes. The TP-Link Archer T2U Nano AC600 showed stable operation during the tests – at 2.4 GHz as well as at 5 GHz; in mains and battery operation. The adapter did not lose the connection to the network even during hours of operation. However, the heat development on the USB interface and the adapter was roughly comparable to the Netgear AC1200. Again, no higher network performance could be found compared to simple 2,4 GHz USB WiFi adapters.

The TP-Link Archer T4U AC1300

The TP-Link Archer T4U AC1300 is — compared with the other two nano-sized adapters — gigantic. Using two antennas and supporting the multi-user MIMO technology, we had no great hope that the adapter would run stable in our tests. Needless to say that the TP-Link Archer T4U AC1300 did not run out of the box. However, it uses the same driver as the Netgear AC1200 (Realtek RTL8812BU), which can be installed in the same way as already described above. After installing the driver, our surprise was big. Even though the authentication process for the wireless network took again an unusually long time and the network manager had to be reset frequently, the TP-Link Archer T4U AC1300 showed higher stability than the Netgear AC1200. The adapter showed stable operation during the tests – at 2.4 GHz as well as at 5 GHz; in mains and battery operation, and it did not lose the connection to the network even during hours of operation. Interestingly, connected with a 5GHz network, the TP-Link Archer T4U AC1300 shows a significantly higher network performance. Random influxes cannot be excluded, but when downloading the LibreOffice package, constant data rates could be detected, which were at least twice as high as with the other two adapters or with simple 2,4 GHz USB WiFi adapters. Possibly the two available antennas with the multi-user MIMO technology come into play here. Also interesting is that the adapter warms up itself and the USB interface only slightly. This is probably due to the significantly larger surface of the adapter and the ventilation holes.

A Raspberry Pi 4 Model B with the "giant" TP-Link Archer T4U AC1300.
A Raspberry Pi 4 Model B with the “giant” TP-Link Archer T4U AC1300.
Conclusion

We stick to the general statement that simple, low-powered USB WiFi adapters lead to fewer problems. This is not only true for power supply, if not used the official power supply for the Raspberry Pi, but especially when searching and installing the necessary network drivers. However, the test also showed that the firmware updates in late autumn 2019 obviously solved many of the electrical supply problems that made the use of more complex USB WiFi adapters virtually impossible. In this sense, the good test results of the TP-Link Archer T4U AC1300 surprised us positively. The purchase of this adapter could be worthwhile not only concerning the availability of the 5 GHz networks but especially also regarding higher throughput due to the multi-user MIMO technology. The TP-Link Archer T2U AC600 also ran very reliably and impressed with its stability. Although it opens up the world of 5 GHz networks, higher throughput rates are not to be expected with this adapter. In contrast, the Netgear AC1200 left somewaht mixed feelings. It also allows docking to 5 GHz networks without providing higher throughput rates. However, in daily use, this adapter makes a much less stable impression. Regularly after a few hours, it loses its connection to the network, which in our opinion, is not acceptable. Probably the biggest problem of all these more complex adapters is that they are not supported out of the box by the Raspberry Pi OS.

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