I have very unique installation situation where I have a single hAP AC Lite (RB952Ui-5ac2nD-TC-US) that's configured with wlan1 as an uplink (mode=station) and wlan2 as the AP. Everything works great, except I also need to be able to connect a single 2.4GHz only client device to the network but my uplink must also be 2.4GHz so I'm left with only 5GHz for the AP. The two devices are less than 24 inches apart, but the 2.4GHz client does not support any other form of connectivity.

Since there is a USB port on the RB952 I'm thinking I could get a USB wifi adapter and add an additional wireless interface to the hAP AC Lite, but have never needed to do so before. Is anyone familiar with some cheap but reliable USB wireless interfaces which will just plug and play in the RB952?

Please no random suggestions of adding additional routers or changing the hAP AC Lite for something else, this is an off grid marine installation that has both space and power budget requirements, and also wired requirements that necessitate 10/100Mbps interfaces as 1Gbps copper ports are not supported (MFD displays are networked using 4 wire half duplex ethernet cables).

On a related note, the more or less now defunct Woobm-USB devices would be great little external wireless adapters for very short distance connectivity like this if MikroTik was able to repurpose them with new firmware (I saw defunct because the web terminal functionality has not worked for me in a couple of years on any web browser I've tried, and hasn't seen a firmware update in years, so the device is now almost useless)

Virtual wlan on itf 1 ?

Done it enough with map lite.
Uplink in station mode and personal wifi via virtual as slave ap on same wifi itf.

Caveat: virtual wil only work when uplink has connection.
Also, don't expect to set any speed records
But it works.

Virtual wlan on itf 1 ?

Done it enough with map lite.
Uplink in station mode and personal wifi via virtual as slave ap on same wifi itf.

Caveat: virtual wil only work when uplink has connection.
Also, don't expect to set any speed records
But it works.

Wait, you can run a virtual AP in mode=AP while the parent interface is in mode=station?? I always thought you could only run a virtual AP if the parent interface was also in AP mode. If I'm wrong (I certainly didn't try that setup), that would solve the problem perfectly.

As for speeds, no worries there as the 2.4 client device only needs to transmit a serial over tcp type signal @115.2k baud, and 90% of the time that it is in use, the parent 2.4GHz interface won't even be connected to anything, and even when it is it's mostly just downloading small weather data files.

Yes.
It's the basis of the road warrior setup using a map Lite.
But be aware of the caveat.

Virtual AP will only work when master station is connected.

Since the interfaces will work in turns, don't forget to increase the buffers of the interfaces to the required size.
I would change the assignment of the interfaces to wlan access point mode on the physical interface wlan1, station mode on the virtual interface wlan3. This is assuming that the uplink access point does not change the frequency

Station mode only works on master interface AFAIK.

I have it working on a virtual

Odd. I never got it working as slave on my map Lite.
Always had to set it on master. But could be because of the way I use it...

Because:
When station mode is set on master, it scans for the network to connect to (I use connect list for multiple targets) and you don't have to bother with frequency settings further on.
When set on ap, the master has to be set manually towards the correct frequency or the slave-station will not connect.
Right ?

When set on ap, the master has to be set manually towards the correct frequency or the slave-station will not connect.
Right ?

Yes

Perfect.
Two flavors of the solution then.

excellent, It'll be a week or so before I'm back there to try this, but this looks promising, all these years I've thought the virtual interfaces had to be mode=ap, and also the master interface as well....

Thanks!

Got to test this over the weekend and it was a success. However it only worked after setting disable-running-check=yes on the master and I had to run the AP on the master and the station on the virtual. Just to see how things worked I also tried configuring it with master=station and virtual=ap, but the client device could not connect.