I have picked up an LHG 5 ac from the storage room that I bought some time ago and decided it was the wrong device to buy, but now I am trying it again.
I need to set it to N with 10 MHz channel width. That selection is available in the winbox settings, however as soon as I select that channel width (or 5 MHz) and save it, the interface list complains in red about "no supported channel".
When I add manual channels with 10 MHz width, they also are rejected.
The actually selected mode (A/N/AC) does not matter, as soon as the 10 MHz width is selected this error appears.

However, when checking the Qualcomm spec sheet of the IPQ4018, the 10 MHz channel width is mentioned.
Unfortunately, the brochure and specs on the MikroTik site do not mention channel width.
I bought a normal LHG HP5 XL instead, and it works fine with 10 MHz channel width.

On this LHG 5 ac I have tried several different firmware versions, at the moment I have even installed v7.1beta6, but the result is the same.

Now I wonder, am I doing something wrong or is this channel width really not supported in the LHG 5 ac, and if so, why does it appear in the selection list for the Wireless configuration (and in the Qualcomm spec sheet)?

I've stumbled on the same thing some time ago. It seems IPQ4018 (and other 802.11ac) chips do not have the software support for 5/10Mhz channel-width. In such case, best is to replace the devices with 802.11n (AR9xxx) routers which do support these channel-widths

Yes, as I wrote above, I did that.
But currently were are facing the situation of eventually migrating from N to AC as undoubtedly AC equipment will be the only thing available in the future, and also we might like to have the additional performance.
So either we would have to change our setup from 10 to 20 MHz channel width (where the ac models can work even in N mode and then maybe in the future switch to AC) or we would remain on 10 MHz channel width but have the ac models work with that in some way, so in the future we still can go to AC without replacing everything.

What I still don't understand is why there is no support for 5 and 10 MHz, even though the chip manufacturer lists these channel widths in their datasheet.
Is the datasheet wrong, is the technical information distributed to the driver writer (MikroTik? or some standard Linux driver distributed by Qualcomm) incomplete?
Or does the driver support it and is there a bug in the configuration software in RouterOS?

The RB921GS-5HPacD (mAntBox 19s) uses a QCA9557 CPU and a QCA9892 wireless chipset and supports 10MHz channels w/o issues.
The OmniTIK 5 PoE ac uses the same QCA9557 CPU and QCA9892 wireless chipset but doesn't support 10MHz.

I've emailed MikroTik support with this question a year ago but they simply said "It may be added in the upcoming version of RouterOS.".
Requested an update a couple of months later, never received a reply. I don't understand their reasoning either.

Ok thanks for that additional info! I got back to trying my LHG 5 ac after I read a remark "it should work in newer software" and that is why successively tried current v6 and v7 betas unfortunately without success.
In this case running v7beta would be an option (those devices are only running as a bridge on a WiFi link, no advanced features like routing). But unfortunately it does not help.

Apologies for my previous conclusion, I tinkered around with some additional equipment of mine, it seems that the limitation is tied to ARM RouterOS architecture which has 802.11ac

Apologies for my previous conclusion, I tinkered around with some additional equipment of mine, it seems that the limitation is tied to ARM RouterOS architecture which has 802.11ac

Yes, but I never understood why "ARM architecture" would have any influence on this kind of things as in RouterOS likely all of the code involved in this will be written in C and just compiled for another processor. So it should be a limitation of functionality of the driver.
But when they know that limitation, why does the UI still show options that are not supported by the driver? My LHG 5HPnD-XL does not show the 80 MHz bandwidth that it cannot support, then why would the ac show a (low) bandwidth it cannot support?

This makes me think/hope that it is "just something I am doing wrong" or maybe a bug. And can still be solved for this model.

Apologies for my previous conclusion, I tinkered around with some additional equipment of mine, it seems that the limitation is tied to ARM RouterOS architecture which has 802.11ac

As the OmniTIK 5 PoE ac is a mipsbe device which shows the same limitation, I'm not sure it is architecture-related at all.

Maybe AC mode would not be useful or not defined in 5 or 10 MHz bandwidth, I don't know. However, a UBNT Powerbeam 5AC does support 10 MHz (not 5 MHz)...
Anyway, even if that is true, the ac models still support N mode as a mode setting, so I would expect that I still can select N mode with 10 MHz channel width and link to an AP in N mode (we use the 912UAG-5HPnD access point at the moment).
That is why I think I am somehow making a mistake: it makes no sense to offer 5 and 10 MHz as bandwidth selection when it would never work, but it could make sense to have certain mode/bandwith combinations that work and others that do not. And the GUI does not change the bandwidth dropdown based on the selected mode.
However, I have not yet been able to find any 10 MHz mode that is accepted on the LHG 5 ac.

Due to lack of response from MikroTik employees I have now created a support ticket for this issue. Let's see what the reply on that will be!

Did you you ever get a Reply to your Support Ticket ? Battling with the exact same Issue.

Yes, I got the reply that it is not possible:

The 5MHz and 10MHz custom channels are supported by the following devices, please see the list below with all devices which support custom channels:
SXT 5 ac (only in 802.11an standard)
SXT 5HnD
SXT G-5HnD
SXT Lite5 ac (only in 802.11an standard)
Metal 5 (not 802.11ac unit)
RB912UAG-5HPnD
RB911-5Hn
RB953GS-5HnT-RP
Groove 52 (not 802.11ac unit)
QRT 5 (not 802.11ac unit)
DynaDishG-5HacD (only in 802.11 an standard)
921GS-5HPacD-15S (only in 802.11 an standard)
921GS-5HPacD-19S (only in 802.11 an standard)

So not the reason why this would not work (when the chip used in the LHG5ac does support it).

Thanks, they should at least say that in their Documentation. As you say, there is actually no apparent Reason. Seems none of the LHG 5 support it.

To Close this Topic, there is actually Reference to Channel Width in the Wiki here https://wiki.mikrotik.com/wiki/Manual:I ... ware_table . Although this Table is not correct, this lists the Disc Lite (Disc-5nD) as 20 and 40 only, but I am running 10Mhz on it. Same with the R52Hn. So it would be interesting to get a complete List, which Routers do actually support 5-10Mhz Bandwidth. IMHO there is little Sense in running ac Routers on 10MHZ, because their Performance will not be better than running on N only, they only get larger throughput on large Bandwidth in ac, If you get more than 100Mbps wireless throughput on N though, ac makes sense as all N Routers I know only have a 100Mbps Ethernet Port and the ac Routers all have 1Gbps Port.

IMHO there is little Sense in running ac Routers on 10MHZ, because their Performance will not be better than running on N only, they only get larger throughput on large Bandwidth in ac, If you get more than 100Mbps wireless throughput on N though, ac makes sense as all N Routers I know only have a 100Mbps Ethernet Port and the ac Routers all have 1Gbps Port.

The reason why I want to use e.g. LHG5 ac in 10 MHz mode is that our current AP operates in 10 MHz N mode and when new users want to join we need to tell them they should buy N devices to be able to use 10 MHz.
That will cause is to be in N mode forever. When AC devices would be able to use 10 MHz mode we could gradually migrate to AC and maybe larger bandwidth in the future.