[OpenWrt-Devel] [OpenWrt] 2.4Ghz limited to 50mW in DFS-ETSI

David Lang david at lang.hm
Thu Jul 30 15:14:50 EDT 2015


What's more, The regulation is on the signal strength of the radiated 
signal, not the transmitter power. so if you go to max transmitter power and add 
a better antenna, you actually exceed the limits.

There is apparently an exception to this for point-to-point use. But you still 
can't use full power + high gain antenna

David Lang

On Thu, 30 Jul 2015, Ben West wrote:

> You can look up your respective country's spectrum regulations.  It is
> possible prior versions OpenWRT didn't fully conform to each regulatory
> domain and were fixed in more recent versions (just as the converse is
> possible).
>
> For example, for the USA, here is a table of power limits for the 2.4GHz
> and 5GHz bands.  Channels 36-48 are limited to 16dBm transmitter power.
> http://www.air802.com/fcc-rules-and-regulations.html
>
> On Thu, Jul 30, 2015 at 3:32 AM, Nicola von Thadden <nico at vthadden.de>
> wrote:
>
>> Hi,
>>
>> I also thought to have used 20dBm or 23dBm in earlier releases (AA).
>> Is there a way to find out to which txpower levels the 5Ghz transceiver
>> is limited? I think the driver reads them out, maybe there is a way to
>> print them on the cmd?
>>
>> But my main problem is the 17dBm on 2.4Ghz when setting DFS-ETSI
>> countries. I don't think that it is a problem of the hardware but of the
>> software parsing the regdom. Maybe there is a fixed limit of 17dBm on
>> non-DFS channels, even when DFS is not required, which is not very
>> useful. Does anyone have an idea where that could be set? My search in
>> the source code had no results until now, where it could be.
>>
>> Thanks
>> Nico
>>
>> On 07/29/2015 06:21 PM, Atanas Vladimirov wrote:
>>> https://dev.openwrt.org/ticket/20201
>>>
>>> On BB I used 20dBm for both 2.4 and 5GHz on the same router.
>>>
>>> Sent with AquaMail for Android
>>> http://www.aqua-mail.com
>>>
>>> On 29 юли 2015 г. 18:40:10 Ben West <ben at gowasabi.net> wrote:
>>>
>>>> This is what I observe running Barrier Breaker on UBNT M5 products,
>>>> too.  I believe the 17dBm limit is intentional, i.e. per regulation.
>>>> The 30dBm tx power limit applies to channels 149 and above, I believe.
>>>>
>>>>>  Also (kind of off-topic): Do you know why 5Ghz channels 36-48 are
>>>> forced
>>>>>  to be 17dBm only on the WNDR3800? I found two possible explanations:
>>>>>  either because of the factory calibration
>>>>
>>>>
>>>> On Wed, Jul 29, 2015 at 10:25 AM, Gerald Matzka <mgerald21 at yahoo.de
>>>> <mailto:mgerald21 at yahoo.de>> wrote:
>>>>
>>>>     Well, it looks like the txpower of your wdnr3800 is limited to
>>>>     17dBm because of the hardware reg-domain settings.
>>>>
>>>>     Kind regards,
>>>>
>>>>     ... sent from my iPhone
>>>>
>>>>    > Am 29.07.2015 um 10:43 schrieb Nicola von Thadden
>>>>     <nico at vthadden.de <mailto:nico at vthadden.de>>:
>>>>    >
>>>>    > Hi,
>>>>    >
>>>>    > I have this strange behaviour down below, for which I also opened
>> a
>>>>    > ticket because I think this should not be like that ;)
>>>>    >
>>>>    > Does anyone have an idea where the problem could originate from
>>>>     and how
>>>>    > to fix it?
>>>>    >
>>>>    > Thanks
>>>>    > Nico
>>>>    >
>>>>    >> On 07/29/2015 12:37 AM, OpenWrt wrote:
>>>>    >> #20222: 2.4Ghz limited to 50mW in DFS-ETSI
>>>>    >> ----------------------+----------------------------------
>>>>    >> Reporter:  nicoduck  |      Owner:  developers
>>>>    >>     Type:  defect    |     Status:  new
>>>>    >> Priority:  normal    |  Milestone:  Chaos Calmer (trunk)
>>>>    >> Component:  kernel    |    Version:  Trunk
>>>>    >> Keywords:  wndr3800  |
>>>>    >> ----------------------+----------------------------------
>>>>    >> I have got a Netgear WNDR 3800 running with openwrt since quite
>>>>     a while.
>>>>    >> I now upgraded to the latest version (trunk) and wanted to use
>>>>     WLAN within
>>>>    >> the regulations here in Germany but also wanted to max out the
>>>>     output
>>>>    >> power (within the regulations).
>>>>    >> Switching the country to Germany limits the maximum output
>>>>     power to 17dBm,
>>>>    >> although it does show as being limited on 20dBm:
>>>>    >> root at OpenWrt:/# iwinfo wlan0 txpower
>>>>    >>    0 dBm (   1 mW)
>>>>    >>    1 dBm (   1 mW)
>>>>    >>    2 dBm (   1 mW)
>>>>    >>    3 dBm (   1 mW)
>>>>    >>    4 dBm (   2 mW)
>>>>    >>    5 dBm (   3 mW)
>>>>    >>    6 dBm (   3 mW)
>>>>    >>    7 dBm (   5 mW)
>>>>    >>    8 dBm (   6 mW)
>>>>    >>    9 dBm (   7 mW)
>>>>    >>   10 dBm (  10 mW)
>>>>    >>   11 dBm (  12 mW)
>>>>    >>   12 dBm (  15 mW)
>>>>    >>   13 dBm (  19 mW)
>>>>    >>   14 dBm (  25 mW)
>>>>    >>   15 dBm (  31 mW)
>>>>    >>   16 dBm (  39 mW)
>>>>    >> * 17 dBm (  50 mW)
>>>>    >>   18 dBm (  63 mW)
>>>>    >>   19 dBm (  79 mW)
>>>>    >>   20 dBm ( 100 mW)
>>>>    >>
>>>>    >> What I did: reset the device, flash it with various builts from
>>>>     trunk and
>>>>    >> try to figure out what was going on.
>>>>    >> I now modified my regdb and was able to isolate the source of
>>>>     the problem:
>>>>    >> country DE: DFS-ETSI
>>>>    >>         # entries 279004 and 280006
>>>>    >>         (2400 - 2483.5 @ 40), (100 mW)
>>>>    >>         # entry 303005
>>>>    >>         (5150 - 5250 @ 80), (200 mW), NO-OUTDOOR, AUTO-BW
>>>>    >>         # entries 304002 and 305002
>>>>    >>         (5250 - 5350 @ 80), (100 mW), NO-OUTDOOR, DFS, AUTO-BW
>>>>    >>         # entries 308002, 309001 and 310003
>>>>    >>         (5470 - 5725 @ 160), (500 mW), DFS
>>>>    >>         # 60 gHz band channels 1-4, ref: Etsi En 302 567
>>>>    >>         (57000 - 66000 @ 2160), (40)
>>>>    >> Thas does not work and has the mentioned behaviour, 2.4Ghz is
>>>>     limited at
>>>>    >> 17dBm. It also does not depend on which values are set in the
>>>>     regulatory
>>>>    >> database for the 2.4Ghz channels, anything over 17dBm will be
>>>>     limited to
>>>>    >> 17dBm.
>>>>    >> running "iw phy phy0 set txpower fixed 2000" gives no error but
>>>>     does not
>>>>    >> change it to 20dBm. Changing the value to anything below 17dBm
>>>>     works
>>>>    >> though.
>>>>    >>
>>>>    >> country DE: DFS-FCC
>>>>    >>         # entries 279004 and 280006
>>>>    >>         (2400 - 2483.5 @ 40), (100 mW)
>>>>    >>         # entry 303005
>>>>    >>         (5150 - 5250 @ 80), (200 mW), NO-OUTDOOR, AUTO-BW
>>>>    >>         # entries 304002 and 305002
>>>>    >>         (5250 - 5350 @ 80), (100 mW), NO-OUTDOOR, DFS, AUTO-BW
>>>>    >>         # entries 308002, 309001 and 310003
>>>>    >>         (5470 - 5725 @ 160), (500 mW), DFS
>>>>    >>         # 60 gHz band channels 1-4, ref: Etsi En 302 567
>>>>    >>         (57000 - 66000 @ 2160), (40)
>>>>    >>
>>>>    >> Thad does work. The only change to the entry above is "DFS-FCC"
>>>>     instead of
>>>>    >> "DFS-ETSI". I can now select any powerlevel between 1 and 20dBm
>>>>     and it is
>>>>    >> also reported as being used:
>>>>    >> root at OpenWrt:/# iwinfo wlan0 txpower
>>>>    >>    0 dBm (   1 mW)
>>>>    >>    1 dBm (   1 mW)
>>>>    >>    2 dBm (   1 mW)
>>>>    >>    3 dBm (   1 mW)
>>>>    >>    4 dBm (   2 mW)
>>>>    >>    5 dBm (   3 mW)
>>>>    >>    6 dBm (   3 mW)
>>>>    >>    7 dBm (   5 mW)
>>>>    >>    8 dBm (   6 mW)
>>>>    >>    9 dBm (   7 mW)
>>>>    >>   10 dBm (  10 mW)
>>>>    >>   11 dBm (  12 mW)
>>>>    >>   12 dBm (  15 mW)
>>>>    >>   13 dBm (  19 mW)
>>>>    >>   14 dBm (  25 mW)
>>>>    >>   15 dBm (  31 mW)
>>>>    >>   16 dBm (  39 mW)
>>>>    >>   17 dBm (  50 mW)
>>>>    >>   18 dBm (  63 mW)
>>>>    >>   19 dBm (  79 mW)
>>>>    >> * 20 dBm ( 100 mW)
>>>>    >>
>>>>    >>
>>>>    >> I have no idea why but there seems to be a bug in the code
>>>>     parsing the DFS
>>>>    >> regulations, limiting 2.4Ghz to lot lower values than allowed.
>>>>     Changing it
>>>>    >> to DFS-FCC works for using the applicaple output power but does
>>>>     not seem
>>>>    >> to be in compliance which German law.
>>>>    >>
>>>>    >> Do you have an idea where the problem could be? I'm happy to
>>>>     try out more
>>>>    >> builds and future versions.
>>>>    >>
>>>>    >> Also (kind of off-topic): Do you know why 5Ghz channels 36-48
>>>>     are forced
>>>>    >> to be 17dBm only on the WNDR3800? I found two possible
>>>>     explanations:
>>>>    >> either because of the factory calibration (is it possible to
>>>>     get them in a
>>>>    >> human readable form somehow? The hexdump is not really readable
>>>>     and I have
>>>>    >> not been able to find the code which pases them) or because
>>>>     these channels
>>>>    >> are considered as "edge-channels" and someone thought it would
>>>>     be safe to
>>>>    >> limit the power, to not disturb any other systems running on
>>>>     even lower
>>>>    >> channels. The latter explanation is kind of weird because it
>>>>     would make no
>>>>    >> sense to limit these 4 channels but no other ones. I find it
>>>>     especially
>>>>    >> strange because that is typically the job of regulatory
>>>>     authorities, to
>>>>    >> define those power levels.
>>>>    >>
>>>>    >> --
>>>>    >> Ticket URL: <https://dev.openwrt.org/ticket/20222>
>>>>    >> OpenWrt <http://openwrt.org>
>>>>    >> Opensource Wireless Router Technology
>>>>    > _______________________________________________
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>>>>     <mailto:openwrt-devel at lists.openwrt.org>
>>>>    > https://lists.openwrt.org/cgi-bin/mailman/listinfo/openwrt-devel
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>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Ben West
>>>> http://gowasabi.net
>>>> ben at gowasabi.net <mailto:ben at gowasabi.net>
>>>> 314-246-9434
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>>>
>>>
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