Via [WayBack] Knowledge Base | AVM International:
3 Setting the maximum transmitter power
- Click “Wireless” (“WLAN”) in the FRITZ!Box user interface.
- Click “Radio Channel” in the “Wireless” (“WLAN”) menu.
- If the option “Set radio channel settings automatically (recommended)” is enabled, proceed with the following section.
- If the option “Adjust radio channel settings” is enabled:
- Click “Additional settings”.
- Select “100%” from the drop-down list “Maximum transmitter power”.
- Click “Apply” to save the settings.
For me, having minimal power was important since every now I needed to be able to connect to it, but only when I was in close proximity.
Hence the settings below: 6% Maximum transmit power is the lowest I could set.
For devices that cannot adjust their antenna output power which have RP-SMA connectors, I bought these to effectively throttle them:
The Wiert Corner - irregular stream of stuff 