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I'm learning about the 802.11 regs. In a book I'm using, "CCNA Wireless 200-355 Official Cert Guide (Certification Guide) 1st Edition by, David Hucaby (Author). Page 53", it has the following clause about 802.11g.

Be aware that 802.11g has the following limitations:

  • It is used in the 2.4GHz band,...
  • OFDM devices are limited to a maximum transmit power of 15 dBm, rather than the 20 dBm limit for DSSS. This is due the way the RF energy is spread across the channel width.

I can't verify this any anywhere else, and it contradicts what I read earlier in the book that the FCC limits the 2.4 GHz ISM band to 30 dBm transmit power and 36 dBm EIRP.

Can anyone verify this or clear this up?

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  • \$\begingroup\$ All applicable FCC documents are here: fcc.gov/wireless/bureau-divisions/… \$\endgroup\$ – Aaron Feb 12 at 19:35
  • \$\begingroup\$ wlan1nde.wordpress.com/2014/11/26/… seems to indicate that 802.11g OFDM transmissions are limited to 20 dBm, at least in Europe. \$\endgroup\$ – auspicious99 Jun 6 at 8:38
  • \$\begingroup\$ Regarding FCC regulations, I've seen before that they specify dBm/Hz, so DSSS transmissions, being spread over a wider bandwidth, can afford to transmit with higher total dBm. \$\endgroup\$ – auspicious99 Jun 6 at 8:39
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Standards and regulations with different scope do not necessary have to enforce identical limitations.

IEEE is an international body which proposes standards. FCC is issuing national regulations. IEEE standards are adopted across industries and sometimes are promoted via a consortium. This way compliance with standards can be enforced by trademarks and patent licensing.

National regulations do not discern between different techniques or trademarks but guard emissions in certain bands.

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