channel 36 transmits at frequency 5180 MHz channel 40 transmits at frequency 5200 MHz channel 44 transmits at frequency 5220 MHz channel 48 transmits at frequency 5240 MHz channel 52 transmits at frequency 5260 MHz channel 56 transmits at frequency 5280 MHz channel 60 transmits at frequency 5300 MHz channel 64 transmits at frequency 5320 MHz channel 100 transmits at frequency 5500 MHz channel 104 transmits at frequency 5520 MHz channel 108 transmits at frequency 5540 MHz channel 112 transmits at frequency 5560 MHz channel 116 transmits at frequency 5580 MHz channel 120 transmits at frequency 5600 MHz channel 124 transmits at frequency 5620 MHz channel 128 transmits at frequency 5640 MHz channel 132 transmits at frequency 5660 MHz channel 136 transmits at frequency 5680 MHz channel 140 transmits at frequency 5700 MHz
But never the channels in between:
5 GHz channels 40MHz
channel 38 transmits at frequency 5190 MHz channel 46 transmits at frequency 5230 MHz channel 54 transmits at frequency 5270 MHz channel 62 transmits at frequency 5310 MHz channel 102 transmits at frequency 5510 MHz channel 110 transmits at frequency 5550 MHz channel 118 transmits at frequency 5590 MHz channel 126 transmits at frequency 5630 MHz channel 134 transmits at frequency 5670 MHz
5 GHz channels 80MHz
channel 42 transmits at frequency 5210 MHz channel 58 transmits at frequency 5290 MHz channel 106 transmits at frequency 5530 MHz channel 122 transmits at frequency 5610 MHz
5 GHz channels 160Mhz
channel 50 transmits at frequency 5250 MHz channel 114 transmits at frequency 5570 MHz
The 20 MHz list is always used. It becomes redundant if the width is wider than 20, and the standard wider band that includes the specified channel will be used. For example if you choose any of 36, 40, 44, or 48 with an 80 MHz bandwidth, the on-air result is exactly the same-- 80 MHz centered over channel 42. Actually setting "42" is not valid.
If you look at the list @psherman linked to, you'll see the 20 MHz channels you list (38, 42, 46, ...) are not available by design. This is to prevent overlap which is a real issue with 2,4 GHz channels.
The wikipedia 5 GHz table is really unclear in how it's structured. The channels are actually structured in the same way as the 6 GHz channels - see the 6 GHz table.
A 40 MHz channel is almost never specified as its center frequency, but as a 20 MHz channel plus a specification of "adjacent" channels. Either 36+adjacent-up or 40+adjacent-down - I forget what the official convention is. At least it seems that wifianalyzer appears to use adjacent-up when displaying things. wifianalyzer will show the center channel in results, but in parentheses show the actual beacon channel. Other systems will only show the beacon channel
Part of this is that for compatibility reasons, beacons are broadcast at 20 MHz bandwidth on known 20 MHz channels. This allows a 20 MHz-only client to join a 40 MHz capable network
For another way of writing it - https://support.huawei.com/enterprise/en/knowledge/EKB1000079063 - specifically this part - "Two neighboring 20 MHz channels are bundled to form a 40 MHz channel. One channel functions as the main channel, and the other as the auxiliary channel. The main channel sends Beacon packets and data packets, and the auxiliary channel sends other packets."
OpenWRT specifies HT40/VHT80/VHT160 by their main channel, not by center frequency, because that's where the beacons get transmitted
Page 7: snip
A few examples (from [9]) will help to illustrate how these parameters work to provide
the center frequency and bandwidth: (Since a VHT STA operates in 5GHz band, the
examples will assume a regulatory class that has a channel starting frequency = 5
GHz.)
Example 1:
A channel specified by
CurrentChannelBandwidth = 80 MHz
CurrentChannelCenterFrequencyIndex1 = 42
CurrentPrimary20MHzChannel = 36
is an 80 MHz channel with
Channel center frequency
= 5 GHz + 5 * 42
= 5210 MHz
I don't thoroughly understand the wording of your inquiry - I'll try though...
If your AP or client is transmitting at 20 or 40 MHz, then yes it will use the appropriate channel:
for 20 MHz that's termed 36, 40, 44, or 48
for 40 MHz that's termed 38 and 46
and yes at 80 MHz - termed 42
Perhaps it'll help if you stop thinking of them as individual channels; but rather as a frequency range used for channels 36-48. As you can see, the larger channel bandwidths are divisible by half of the next size.
(The graphic shows that.)
Maybe it will also help to remember that you have to pick a 20 MHz channel - as the AP will decrease its TX bandwidth if there's congestion, etc. on the band.
Yes. OpenWrt follows the standard for the 80 MHz blocks, such as "channel 42" covering the four 20 MHz channels centered over 36,40,44,48. It will not transmit an 80 MHz signal that is not one of the standard blocks.
The reason I ask is that ONLY 36 works for me and I am not sure why.
Also would it make sense to have the UI update so that when the band width is selected the correct channels are displayed with the standard format (center channel)
If you haven't set a country, or you are in a country where only the low part of the band is allowed, then 80 MHz will only work on that first block 36-48 or "42".
One thing to also keep in mind is that there is a 90 second "listening for radar interference" clock that must run and expire when you switch to, or power up on a DFS channel in a DFS regulated country such as the US. This applies to 60, 100, 116, and 132, etc.
After changing the location to US i was able to select a less crowded band (116) and all is working. Thanks again for the assistance @mk24 and @Almondo
So the standard way of assigning channels is this. Notice when selecting a 40 or 80 Mhz channel the center channel is chosen. So if i set the dropdown in the UI to 80 only channels 42, 58, 108, 122, 138, 155 should be available for selection.
OR (and this is even more correct) if we use center frequency there will be 0 overlap in channel numbers which is how the bandplan was designed. There is no need to even allow selection of band width. Each channel will correspond to its correct bandwidth.
So:
36 (20Mhz)
38 (40Mhz)
40 (20Mhz)
42 (80Mhz)
44 (20Mhz)
46 (40Mhz)
48 (20Mhz)
50 (160Mhz)
and so on
This is the point of using center channel in the bandplan. Each channel number corresponds to its bandwidth and bandwidth never needs to be selected.
Maybe it will also help to remember that 
