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Tony359
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hAP ac3 - Unable to select channel 11

Wed Dec 21, 2022 11:07 am

Hi all,

I would need to set channel 11 on my hAP ac3 as someone has set an overlapping wifi on channel 3.

I understand that channel 11 has a centre frequency of 2462 which is not in the drop-down list of my router. I can manually select it and it works but if I check after a few days the router is back to "auto" and it selects channel 6 I think.

Can someone please help me? I am on RouterOS 7.6

Thanks
Tony
 
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Re: hAP ac3 - Unable to select channel 11

Wed Dec 21, 2022 11:12 am

Can you please share:

/interface/wireless/ export hide-sensitive
 
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Re: hAP ac3 - Unable to select channel 11

Wed Dec 21, 2022 11:40 am

of course, thank you! (I've masked some data with xxx)

interesting, I see 2462 as 2Ghz interface frequency but the GUI reports "auto". 5Ghz is intentionally on a separate SSID and hidden.
# dec/21/2022 09:37:17 by RouterOS 7.6
# software id = FB1B-LQD8
#
# model = RBD53iG-5HacD2HnD
# serial number = xxxxxxxxxxxxxxxxx
/interface wireless security-profiles
set [ find default=yes ] supplicant-identity=MikroTik
add authentication-types=wpa2-psk mode=dynamic-keys name=xxxxxxxxxx\
    supplicant-identity=""
/interface wireless
set [ find default-name=wlan1 ] band=2ghz-b/g/n channel-width=20/40mhz-XX \
    country="united kingdom" disabled=no distance=indoors frequency=2462 mode=\
    ap-bridge name=wlan1-2Ghz security-profile=xxxxxxxxxxxxx ssid=xxxxxxxxx \
    wireless-protocol=802.11
set [ find default-name=wlan2 ] band=5ghz-a/n/ac channel-width=\
    20/40/80mhz-XXXX country="united kingdom" disabled=no distance=indoors \
    frequency=auto hide-ssid=yes mode=ap-bridge name=wlan2-5Ghz \
    security-profile=xxxxxxxxxx ssid=xxxxxxxxxx wireless-protocol=802.11
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erlinden
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Re: hAP ac3 - Unable to select channel 11

Wed Dec 21, 2022 11:55 am

UInless you live in a place where there are no nearby Wifi networks, you could better not set a 40MHz bandwidth on the 2.4GHz radio. Instead, turn extension channel off.

Besides (though no problem related), configure extension channels manually (i.e. Ceee), otherwise there is no predictable outcome which control channel is used.
And at last...hidden is like...not hidden. It is just not shown by default in wireless clients.
 
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Re: hAP ac3 - Unable to select channel 11

Wed Dec 21, 2022 12:10 pm

Thank you.

I'm a bit confused as I previously diagnosed a slow wifi and I was told to leave factory defaults here:

viewtopic.php?p=970187

Where can I find the extension channel option?

So by setting 20Mhz on the channel I tell the router NOT to extend the wifi over adjacent channels? I learnt that for best wifi we should use channels 1, 6 and 11 - wouldn't that give 40Mhz of bandwidth to those channels? With 40Mhz I would overlap from channels 9 to 13. I am not questioning your advice, just trying to understand myself.

As long as the 5Ghz is not shown on Windows and Mac I'm ok - we know it's there and available, I just don't want computers to automatically show it. I need the long reach of 2Ghz, not the high speed of 5Ghz.

Thank you so far.
 
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Re: hAP ac3 - Unable to select channel 11

Wed Dec 21, 2022 12:28 pm

Factory defaults work...well, optimization should be done afterwards.

Every channel (1, 2, 3...11) in 2.4GHz is 5MHz wide. By choosing channel 1,6 or 11, you choose 20MHz it total (hence the adjacent channels). If you select to use extension channel (channel width) instead of using 20MHz you use 40MHz. Which is terrible, unless... Choose 20MHz Channel Width on the 2.4GHz radio and check if that solves the problem. You will do yourself and you neighboors a favor :D

[Update]The link describes optimization on the 5GHz radio. There is more bandwidth and it can be usefull to use extnsion channels to get better performance. Still it could cause additional interference.
 
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Re: hAP ac3 - Unable to select channel 11

Wed Dec 21, 2022 12:30 pm

One image should tell more than quite a few words:

Image

Taken from wikipedia article on WiFi channels (it's well worth reading, either this or one of other similar ones).

Note that picture above doesn't apply in Northern America where channels 12 and 13 are off limits for use with anything newer than 802.11b. There the slimmed version applies:

Image

The channel number shown on (lone) 40 MHz channel is not correct, it's actually channel 1+5 (same as on top picture).
 
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Re: hAP ac3 - Unable to select channel 11

Wed Dec 21, 2022 1:57 pm

I understand, thanks for explaining that in details.

I agree that in a crowded environment, 20Mhz at 2.4Ghz is definitely recommended. I did not realise I was flooding the frequency spectrum! :)

So to switch to 20Mhz width I just select "20Mhz" under "Channel width" and then select channel 11 (2462), is that correct? Any other tweaks you'd recommend? Looking at your previous post, do I "turn extension channel off" when I tell the AP to use 20Mhz width?

Cheers!
 
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Re: hAP ac3 - Unable to select channel 11

Wed Dec 21, 2022 2:10 pm

Yes, that's just fine.

My recommendations
  • You can turn off WPS Mode (from a security perspective).
  • Don't use 802.11a/b unless absolutely necessary
  • Set WWM on (advanced settings)
  • Optimize Rx Power (advanced settings)
 
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Re: hAP ac3 - Unable to select channel 11

Wed Dec 21, 2022 3:30 pm

Thank you, I appreciate your advice.

Can I check what you mean with "optimise RX power" please? I cannot find an option for that in Advanced mode and google does not help either.

Thanks!
 
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Re: hAP ac3 - Unable to select channel 11

Wed Dec 21, 2022 3:46 pm

I think it was a typo Tx power.
2022-12-21_17-14-37.jpg
https://wiki.mikrotik.com/wiki/Manual:Wireless_FAQ
2022-12-21_17-12-00.jpg
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Re: hAP ac3 - Unable to select channel 11

Wed Dec 21, 2022 3:52 pm

Thanks @own3r1138, I indeed made a tpo.
Can you let us know how things go after making the adjustments, @Tony359?
 
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Re: hAP ac3 - Unable to select channel 11

Wed Dec 21, 2022 4:14 pm

Thank you both! is 17dBm the maximum? I assume this way we prevent the AP from changing things around.

I shall do of course but I would like to change those options when I am on site - so it'll take a few weeks.

But thanks for your help so far :)
 
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Re: hAP ac3 - Unable to select channel 11

Sun Jan 29, 2023 12:49 pm

I'm back on site and changed the channel width, thanks!

I was reviewing the thread and I would like to double check the "optimise TX power" subject. I see Mikrotik does NOT recommend to set "all rates fixed" but the above screenshot is set that way.

Can I please check with you what is the best setting for a reliable signal?

Thanks so far!
 
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Re: hAP ac3 - Unable to select channel 11

Sun Jan 29, 2023 1:12 pm

the above screenshot is set that way.
For the screenshot, I put it to all rates fixed so it could enable the value.
 
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Re: hAP ac3 - Unable to select channel 11

Sun Jan 29, 2023 1:38 pm

Thanks. I understand that you need to enable "all rates fixed" to enable the value field but I am referring to this:


datarate.PNG


It looks like Mikrotik is explicitly not recommending that setting. What is your thought on that?

Thank you!
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Re: hAP ac3 - Unable to select channel 11

Sun Jan 29, 2023 2:14 pm

Well, I don't have enough knowledge to comment on this.
 
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Re: hAP ac3 - Unable to select channel 11

Sun Jan 29, 2023 2:55 pm

When you want to set "all rates fixed" you should set a lower Tx power than the maximum.
Look what powers it sets when you use "default" (automatic power selection depending on country, antenna, and rate) and set a Tx power lower or equal than the lowest power you find there (in the first column).
E.g. when the max power is 17dBm that would be 14dBm or lower.
 
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Re: hAP ac3 - Unable to select channel 11

Sun Jan 29, 2023 2:56 pm

Thanks, I appreciate your help anyways.

I guess my question is for @erlinden then. Can I know more about "optimising TX power"?
 
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Re: hAP ac3 - Unable to select channel 11

Sun Jan 29, 2023 3:01 pm

Well, under hypothetical ideal circumstances, e.g. when you are living out in the desert in a building with 10 access points, it could be that you can optimize the installation by not running everything on full power. Each AP only needs to cover an area, and the Tx power can be set to cover only that area, and not the whole building.
Then you can reduce the noise from the other APs when you re-use the channel at another place.

Of course in the real world you have to deal with APs outside of your control, which the owner has set to max legal power and beyond.
It is kind of an arms race. Reducing your own power will not improve things for you, but only for your neighbor. And it can be difficult to convince them to do the same and make it better for both of you.
 
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Re: hAP ac3 - Unable to select channel 11

Sun Jan 29, 2023 3:33 pm

A couple of years ago one of MT staffers explained the way Tx power worked at that moment. It was in heat of discussion about why Mikrotik removed possibility to set antenna gain (via GUI) and why there was hard-coded minimum antenna gain set on most devices[*]. I can't find that forum thread right now ....

Anyway, here's how Tx power is limited:
  1. country regulations of maximum EIRP. This figure includes all Tx chains (so in case of massive MIMO, power per chain and thus beacon gies down considerably) and crucially it includes antenna gain.
    Thus value is set with selection of country, can be channel-specific and is legaly binding for both equipmnent nanufacturer and device owner/administrator. While local radio spectrum inspectors might not visit every homeowner (unless somebody important complains because of interference, such as local ATC or meteorological service), regulatory agencies (such as FCC) will push on manufacturers to make things as correct as possible.
  2. Tx power amplifier (often integrated in SoC) power limit.
    This limit is often rate-dependent due to low quality of low-cost power amplifiers. This low quality means imprecission of power output (smearing of QAM symbols) which means self-made interference. Excerpt from the list is published on product pages of all MT wifi devices - the table(s) under "Wireless specifications".
  3. user set maximum Tx power
    This can be set per rate.

And the way Tx power control works is to frequently evaluate all 3 limits and then adjust actual Tx power to the lowest value. Which means it should be safe to set Tx power to "all rates fixed" with value exceeding some of figures from the table mentioned in bullet #3 above.

There was some discussion about why it's not fine to have Tx power for all rates set to the same value. The effect of setting Tx power for higher rates at lower values is that when a device approaches cell border, throughput will reduce. If power for high rates is set to same value as for low rates (and is lower than chipset limit), then client will enjoy higher data rate right to the point of loosing cell coverage.
In reality it's not like that. Receiver sensitivity plays equally important role and for most devices (client devices as well as APs) it drops at higher rates much more than Tx power.


[*] People traditionally used antenna gain setting as means of reducing Tx power ... as explained in bullet #1 antenna gain is part of equation of EIRP which is limited. With higher setting of antenna gain Tx power has to be reduced not to exceed legal limits. It also seems that when using Tx power table, ROS actually dismissed other bullets in the list above. Meaning that indeed it was possible to push Tx powef amplifier over its limits (as @pe1chl warns in post preceeding his last one). However if Tx power logic was indeed changed as was expkained by MT, then this consideration is not valid any more.
 
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Re: hAP ac3 - Unable to select channel 11

Sun Jan 29, 2023 3:45 pm

When considering low power installations one has to consider also SINR figure. If there are no interferers (other APs operating on same or adjacent channels, bluetooth, wireless UDB mice, microwave owens, ...), then there's still thermal noise floor of environment and Rx sensitivity, which both lower SINR value. And for faster transfer rates it's important to keep SINR above certain value (again depends on datarate requirements).

Which means that lowering Tx power indeed reduces interference to adjacent APs, but if overdone it also reduces performance. And reduction of Tx power only really helps in adjacent APs if they use overlapping frequency channels. This is a big problem in 2.4GHz spectrum (only 3 non-overlapping channels in US or 4 non-overlapping channels in Europe, depends if channels 12 and 13 are available or not) and smaller problem in 5GHz spectrum. If one is operating in the middle of nowhere and needs to run gazzilion of APs, then it would probably be better to use 20MHz channels also on 5GHz (which is something almost nobody does) because there will be 4x the number of non-overlapping channels performing much better than 80MHz channels with fair share of interference.
 
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Re: hAP ac3 - Unable to select channel 11

Mon Jan 30, 2023 4:33 pm

Thank you

I think I understand. I thought it was some quick setting to change but - as you clearly explained - it depends on many factors, many of which might not be under my control and might change over time.
I think I'll bear in mind this option if I ever ran into issues but for now I believe the default setting will do: I am not often on site and there are a gazillion other APs sharing the same channel so I doubt that setting a specific TX power would work permanently - but my knowledge on the subject is limited.

For now, thanks all for your support, I'm glad I managed to switch the channel to 20Mhz.

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