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Date:   Mon, 9 Nov 2020 19:42:28 -0600
From:   Seth Forshee <seth.forshee@canonical.com>
To:     bkil <b.K.il.h.u+tigbuh@gmail.com>
Cc:     wireless-regdb@lists.infradead.org, linux-wireless@vger.kernel.org
Subject: Re: [PATCH] wireless-regdb: restore channel 12 & 13 limitation in
 the US
Message-ID: <20201110014228.GJ6125@ubuntu-x1>
References: <840438bf70c72d2ab933aee9ae5aa6985b6c1531.1601902881.git.b.K.il.h.u+tigbuh@gmail.com>
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On Mon, Oct 05, 2020 at 03:01:22PM +0200, bkil wrote:
> The precisely allowed transmission power on channel 12 & 13 is not clear.
> 
> I did some fact checking and document reviews in the past, but still
> failed to come up with an exact reference or calculation regarding what TX
> power should be allowed in general to reduce interference in the
> neighboring restricted band 2483.5-2500 MHz and whether indoor vs. outdoor
> and b/g/n modulation would make a difference (probably yes).
> 
> Existing documents that discuss this are vague and pretty much out of date:
> https://en.wikipedia.org/wiki/List_of_WLAN_channels#endnote_B
> 
> Following these guidelines, I failed to come up with an approximate
> formula that would prohibit usage of channel 12 & 13, but still allow
> usage of channel 11 with full power, hence at least part of the argument
> for prohibiting channel 12 & 13 needs to be refined.
> 
> Until further research, just to stay safe, I propose that we restore the
> previous limitation of disabling channel 12 & 13 as before. We should
> work towards finding a safe transmission power to use on both and specify
> that (like 50mW on channel 13 and 100mW on channel 12?).
> 
> I've also started a discussion for investigation on Wikipedia:
> https://en.wikipedia.org/wiki/Talk:List_of_WLAN_channels#Should_the_2.4GHz_channel_12_and_13_in_the_USA_need_updating?
> 
> Signed-off-by: bkil <b.K.il.h.u+tigbuh@gmail.com>

I tried doing a little research, and it does appear that use of channels
12 and 13 is more complicated than it might seem on the surface. I
cannot find any clear guidance on power limits and lack the background
to determine appropriate limits from the information I did find, so it
does seem prudent to restore the previous limitation.

Applied, thanks!

> ---
>  db.txt | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/db.txt b/db.txt
> index ac32483..68613cf 100644
> --- a/db.txt
> +++ b/db.txt
> @@ -1568,8 +1568,12 @@ country UG: DFS-FCC
>  
>  # https://www.ecfr.gov/cgi-bin/text-idx?SID=eed706a2c49fd9271106c3228b0615f3&mc=true&node=pt47.1.15&rgn=div5
>  # Title 47 Part 15 - Radio Frequency Devices, April 2, 2020
> +# Channels 12 and 13 are not forbidden, but are not normally used with full
> +# power in order to avoid any potential interference in the adjacent restricted
> +# frequency band, 2,483.5–2,500 MHz which is subject to strict emission limits
> +# set out in 47 CFR § 15.205. TODO: reenable and specify a safe TX power here.
>  country US: DFS-FCC
> -	(2400 - 2483.5 @ 40), (30)
> +	(2400 - 2472 @ 40), (30)
>  	# 5.15 ~ 5.25 GHz: 30 dBm for master mode, 23 dBm for clients
>  	(5150 - 5250 @ 80), (23), AUTO-BW
>  	(5250 - 5350 @ 80), (23), DFS, AUTO-BW