The device 2.4G uses sst12lp15b power amplifier, When I set the country code to CN, the maximum txpower should be set to 20dbm, but it will actually be limited to 16dbm, If I set the country code to us, I can use txpower of 20dbm normally, But after doing so, I will not be able to use 12 and 13 channels
The second problem is that if 2.4G and 5G WiFi are set to different country codes, there will be a conflict, and only one of them will be used
OpenWrt version is 21.02.1 r16325-88151b8303
D-Link (in CALDATA) must have reduced the power either because of noise or regulations when this router was released. If using regdb, not sure you would want to hack your own.
Besides, I wouldn't trust too much what the UI says. It could well say 24dbm but in reality the hardware is only doing 16dbm because of hardware limitations. Unless you have sophisticated equipment to measure it, no way to know.
To be compliant with regulations you should set the country code to the country where the router is operating... but nothing stops you in OpenWRT from not doing so.I remember discussions either here or in other forums about region shopping to try find the "best" configuration possible. So... provided you understand the implications... Japan? Austria?
As you mention, both radios need to be on same domain, so check also the 5GHz band regulations. Setting the domain to a country other than where the router is may not be a good idea, but setting it to a domain that causes it to interfere with DFS is a bad one. Not sure what CN regulatory domain specifies for 5GHz.
Because I can only set 2.4GHz to US to use 20dbm txpower, The specification of CN completely includes the channel of US, And almost all routers sold in the Chinese market have 20dbm txpower.
Because the 2.4GHz country setting will affect the 5GHz setting, the 5GHz setting will also become US, The 5GHz channels of CN specifies are different US, Therefore, I must set 2.4GHz and 5GHz to different country codes, But it doesn't work as expected
Well, it's a pretty old draft 11n router (I have a few of them, love 'em, they work well) but can't expect them to be as flexible as something released last year.
What is the TX power that you get if you set the country to Austria or New Zealand?
If you set a country other than CN just make sure you set your 5GHz radio to a valid CN channel (36 to 48 or 149 to 165), as use of channels 52-64 & 100-140 might show as available but their use seem to be prohibited in China.
Japan.
Tested on a DIR-825 C1 so pretty much what you have.
Japan enables channels 12 & 13 (2.4 GHz) and allows 20 dBm (100 mW) on both. Drawback is it does not enable channels 149 - 165 (5 GHz)... but you still get 36 - 64 to play with.
WARNING - Japan enables channel 14 @ 2.4 GHz. Don't use it! Never set the channel to "auto"!
WARNING - Japan enables channels 100 - 140 @ 5 GHz. Don't use them! Don't set the channel to "auto"!
BEWARE - setting your router to anything but the country it is operating in will make it non compliant with regulations. You take full responsibility for that and any trouble that might bring you. I don't think the risks of getting fined or worse for operating non-compliant radio equipment is worth the additional 2.4GHz Tx power. Besides, that may help a remote device hear the router... but will that device be able to scream back to the router? It will probably also be capped at 16 dBm when Tx back.
Some reading that looks like it comes from someone who knows about this business: https://metis.fi/en/2017/10/txpower/ .
Thank you for your reply, I have tried to set the country to AU before, which is the same, with a maximum of 16dbm, In my actual use, I feel that the 20dbm of this router is far less than that of my other routers, I tried the original firmware of D-Link, and the effect is the same, So I suspect there may be a hardware problem
Again... try Japan.
Don't place the channels on Auto.
Do a survey and pick a valid one of 1-13 for 2.4GHz, and 36-44 for 5GHz.
You'll get your 20dBm that way.