The above diagram shows the FCC maximum transmit power limit for Standard Power Access Points and client devices. As mentioned in the Regulatory Information section, the Standard Power Access Points get the allowed power limit and the channels available at their specific geographic location from the AFC system. It is possible for the maximum power limit at that location to be less than the 36 dBm for AP and implicitly 30 dBm for client. Also, the SP client device must always set its maximum transmit power 6 dB below the maximum transmit power of the SP AP.
For example, if we assume that the AFC database indicates the maximum power limit for the Standard Power AP is 29 dBm, then the client maximum transmit power is 23 dBm.
Another point to consider is that mobile devices would limit the maximum power to values lower than regulatory limit to be more effective due to various physical and design constraints.
AFC Standard Power TX Power Limit
For Standard Power the SNR (Signal to Noise Ratio) decreases with channel width increase because the noise floor doubles (adds 3 dB) with each doubling of the channel width. This is illustrated in the next diagram
