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ALFA Adapters — Troubleshooting Index

排查鐵律（Diagnosis iron rule）: Hardware first → driver second → configuration last. More than 80 % of "my ALFA is broken" reports turn out to be a power issue, a missing DKMS rebuild, or a kernel-update side effect — not a dead adapter. Follow the tree below before you blame the hardware.

ALFA adapter troubleshooting decision tree — hardware, driver, then configuration

Problem classification index​

CategoryTypical issues
DetectionAdapter not in lsusb, no interface, disappears after reboot
DriverDKMS build fails, module not loaded, firmware errors in dmesg
ConnectionWon't associate, drops constantly, slow link
Monitor modeairmon-ng fails, injection test fails, no frames captured
PowerAdapter dies under load, works on one PC but not another
RegulatoryWrong channel set, TX power capped, "5 GHz channels missing"

Every chipset has its own deep-dive page — bookmark yours:

ChipsetAdaptersDriver page
MT7612UAWUS036ACMmt7612u
MT7610UAWUS036ACHMmt7610u
MT7921AUNAWUS036AXM / AWUS036AXMLmt7921aun
RTL8812AUAWUS036ACHrtl8812au
RTL8811AUAWUS036ACSrtl8811au
RTL8832BUAWUS036AX / AWUS036AXERrtl8832bu
RTL8821CUAWUS036EACSrtl8821cu

Issue 1: Adapter not detected at all (lsusb empty)​

Symptom​

Plugged in, LED may or may not light, and lsusb shows no Realtek/MediaTek line.

Diagnosis​

lsusb
dmesg | tail -30

Look for device descriptor read/64, error -71 or device not accepting address in dmesg — classic power-handshake failures.

Root cause​

Almost always USB power or cable — especially on the high-power models (AWUS036AXM/AXML, AWUS036AX) connected to a front-panel port or an unpowered hub.

Fix​

  1. Try a rear USB port (or the USB-C port via an adapter).
  2. Try a different cable — some cheap USB-C cables are charge-only.
  3. Use a powered USB hub.
  4. On a laptop, unplug other high-power USB devices.
  5. If still invisible on two different computers, the adapter is faulty — contact support.

Issue 2: lsusb sees it, but no wlanX interface​

Symptom​

lsusb shows the adapter; iw dev / ip link show nothing.

Diagnosis​

dmesg | grep -iE "wlan|firmware|error"
lsmod | grep -iE "mt76|8812|8811|88x2|8821"

Root cause​

Two common causes:

  • Realtek chipsets: the DKMS module was never loaded (or failed to build after a kernel update).
  • MediaTek Wi-Fi 6E: the kernel is older than 5.18 (mt7921u missing) or firmware blobs are absent.

Fix​

  • Realtek: sudo modprobe 8812au (match your chipset), and add it to /etc/modules-load.d/alfa.conf so it auto-loads on boot. If modprobe says Module not found, rebuild: sudo dkms autoinstall.
  • MediaTek: sudo apt install linux-firmware and reboot. Kernel too old? Upgrade the OS — see the compatibility matrix.

Issue 3: DKMS build fails after a kernel update​

Symptom​

"Adapter stopped working" right after apt upgrade; dmesg shows 8812au: version magic ... should be ....

Diagnosis​

dkms status

If your module shows Error! or a broken kernel-version entry, that is the problem.

Root cause​

The driver's DKMS recipe could not rebuild against the new kernel — usually missing headers, or the repo is too old for a brand-new kernel.

Fix​

  1. Install headers: sudo apt install linux-headers-$(uname -r)
  2. Force rebuild: sudo dkms autoinstall
  3. Still failing? Update the driver repo and reinstall: 
    cd /opt/rtl8812au && sudo git pull && sudo make dkms_install
  4. Reboot and check dkms status again — it should list your module as installed.

Issue 4: Monitor mode starts but injection test fails​

Symptom​

airmon-ng start succeeds, wlan0mon exists, but aireplay-ng --test reports 0/30 or Failed.

Diagnosis​

sudo aireplay-ng --test wlan0mon
sudo iw dev wlan0mon info   # confirm it really is type monitor

Root cause​

Driver built without proper monitor/injection support, or you are on a channel no AP is using (injection needs an AP beacon to reply to), or the RF environment is empty (isolated lab).

Fix​

  1. Lock a channel with active APs: sudo iw dev wlan0mon set channel 6
  2. Retest. Still 0/30? Rebuild with the aircrack-ng driver repos, which ship monitor + VIF enabled by default:
  3. In a dead RF zone, create your own AP with a phone hotspot on the same channel.

Issue 5: Wi-Fi drops or is slow​

Symptom​

Link connects then drops every few minutes; throughput far below the class rating.

Diagnosis​

iw dev wlan0 link          # signal + tx rate
iw reg get | head -20      # regulatory domain

Root cause​

  • Regulatory domain: if iw reg get shows country 00 (unset), TX power is capped at the default 20 dBm limit.
  • Power saving: aggressive USB power management throttles the radio.
  • Overheating: sustained TX on high-power adapters.

Fix​

  1. Set your region: sudo iw reg set TW (or your country code).
  2. Set TX power: sudo iwconfig wlan0 txpower 30 (max legal for your domain).
  3. Disable power save: sudo iwconfig wlan0 power off.
  4. Prefer a USB 3.0 port for AC1200+ adapters — USB 2.0 caps throughput.

Issue 6: 5 GHz channels missing​

Symptom​

Only 2.4 GHz networks visible; iwlist wlan0 freq shows no 5 GHz entries.

Root cause​

The regulatory domain is unset or restricted (often country 00 on fresh installs), so the driver refuses 5 GHz channels.

Fix​

sudo iw reg set TW    # replace with your country code
sudo ip link set wlan0 down && sudo ip link set wlan0 up

Still not solved?​

Before you give up, collect this exact information and contact us (or the driver project) — it is what a maintainer needs to help you:

uname -r
lsusb
dkms status
dmesg | tail -50
iw dev

Attach all of the above plus: your adapter model, the OS/kernel, and the exact command whose output surprised you. One more thing worth checking — the hardware integration guides if you are running a Jetson, Raspberry Pi or Unitree robot; embedded boards have their own power and driver quirks.