TP-Link make a cool little USB Wi-Fi adapter called the TL-WN725N.  I’ve just discovered something that may explain some of the connectivity issues folks are having with it.  The same issue is probably affecting a variety of other wireless devices as well.

A while ago, I needed a USB Wi-Fi adapter that would work with zero configuration on a Ubuntu 18.04 LTS system.  The TP-Link TL-WN725N fit the bill.  Version 3 of the adapter currently sells for a mere $11 from PC Case Gear.  You just plug it in, turn the computer on, the kernel already has the correct driver support so the adapter is automatically detected, just go to your Wi-Fi menu, select your network, enter the password, and you’re done.  Couldn’t be easier.  Worked fine for months.

As a result of an extended NBN outage, I had to temporarily re-jig the network to get our Internet connection back up and running.  In so doing, I made a few changes to our wireless router (a FritzBox 7490) that resulted in the computer with the WN725N Wi-Fi adapter unexpectedly dropping off the network.

The tech specs for the WN725N say that it operates in the frequency range of 2.400–2.4835GHz.  The FritzBox lets you centre your wireless network anywhere from Channel 1 (2.412GHz) to Channel 13 (2.472GHz).  Since the WN725N covers all of the channels that the router can transmit on (including two side channels on either end) I chose to centre the network on Channel 12 (2.467GHz) to avoid interference with other nearby Wi-Fi networks.  Doing so resulted in the WN725N dropping off the network immediately.  The network was no longer even visible in the list of available networks.

Experimentation revealed that the WN725N was only able to see (and connect to) wireless networks centred on channels 1 through 11.  Centring the network on channels 12 or 13 would result in a disconnect and prevent reconnects.

Now, the FritzBox 7490 defaults to “Auto channel” when you make changes to the radio channel settings:

What that means is that — depending on interference — the FritzBox could choose to centre the wireless network on any channel from 1 to 13.  That includes the two channels (12 and 13) that the WN725N is incompatible with.  Since the process of selecting a channel is completely invisible to end users, a wireless network connection that was working one day (or even moment) could suddenly stop working, and the network would seem to vanish.

So, if you have a TP-Link WN725N, or some other wireless device, that seems to inexplicably drop off the network, and the network is then not even visible, it might be because your router — in order to minimise interference — has moved the centre of your wireless network to a channel that is incompatible with your device.  Log into the router and make sure that it only centres the network on channels 1 through 11 (inclusive).  If you can’t limit the range, then you should at least be able to manually set the channel.  To minimise interference, it’s generally a good idea to set it to either channel 1, 6 or 11.

Note that this is not a hardware fault.  It’s an interoperability issue that results in connectivity problems on edge cases.  Both the adapter and the router are doing their best to give you a good connection.  They sometimes, unfortunately, do not agree on exactly how that should be accomplished.   You just need to instruct the router to not try and be too clever and the two will get along just fine.  😉

Take it easy.