Monitoring mode is not silent - scan transmits on every frequency.

[gasparka]

Tested with

• Delock USB 2.0 Dual Band WLAN ac/a/b/g/n Stick
• AWUS036ACH

Using iw e.g. iw dev mon1 scan passive (note that the passive flag has no effect). This results in packet transmitted on scanned frequencies. In addition, i have witnessed TX when device is idle (in monitoring mode)!

I am very grateful for any hints on how to achieve radio silence in monitoring mode.

[gasparka]

Findings today:

• Using airodump-ng is better but not silent - seems to transmit when new AP is found!?
• iw scan sends packet on each frequency scanned - hopeless.
• Network manager performs periodic scans (even after nmcli radio wifi off). Fix: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/configuring_and_managing_networking/configuring-networkmanager-to-ignore-certain-devices_configuring-and-managing-networking. This also fixes TX during system boot.
• https://github.com/morrownr/8821au-20210708 driver is silent during airodump-ng!, iw scan still transmits.
• For anyone doing similar measurements: Cheapo spectrum analyzers will miss the TX -even if using maxhold- because the pulses are very short. I recommend using instantaneous bandwidth of 80MHz and sitting at 2.44GHz. Here is an example of iw scan: My test system is Jetson Nano running Ubuntu 18.04. Cheers :)