[OpenWrt-Devel] ath9k: Max 3 dBi gain for FCC (365-ath9k-adjust-tx-power-reduction-for-US-regulatory-do.patch)

Sven Eckelmann sven.eckelmann at openmesh.com
Tue Jul 31 04:57:03 EDT 2018


I've just checked the FCC "antenna reduction workaround" patch [1] in ath9k. 
The code uses twicepower (.5 dB unit used by QCA) and uses 6 (3dBi) as allowed 
gain for FCC. The comment also states "FCC allows maximum antenna gain of 
3 dBi".

Where does the 3dBi come from? 15.247(b)(4) talks about 6 dBi [2]:

> (4) The conducted output power limit
> specified in paragraph (b) of this section
> is based on the use of antennas
> with directional gains that do not exceed
> 6 dBi. Except as shown in paragraph
> (c) of this section, if transmitting
> antennas of directional gain greater
> than 6 dBi are used, the conducted
> output power from the intentional radiator
> shall be reduced below the stated
> values in paragraphs (b)(1), (b)(2),
> and (b)(3) of this section, as appropriate,
> by the amount in dB that the
> directional gain of the antenna exceeds
> 6 dBi.

Btw. I am not sure whether all countries which use the FCC DFS rules also use 
the same antenna gain limits. But let us assume for now that this is ok.

Kind regards,

[1] https://github.com/openwrt/openwrt/blob/81542331cb1827650f3abd69375d964d0ce2d050/package/kernel/mac80211/patches/365-ath9k-adjust-tx-power-reduction-for-US-regulatory-do.patch
[2] https://www.gpo.gov/fdsys/pkg/CFR-2013-title47-vol1/pdf/CFR-2013-title47-vol1-sec15-247.pdf
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