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

[Sven Eckelmann]

Hi,

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,
	Sven


[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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