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Hi mazbio,

There are three license-free ISM bands. They are the 900 MHz. 2.4 GHz, and 5.8 GHz bands. Of these, the FCC has specified that wireless LANs may use the 900 MHz and 2.4 GHz bands.

Since the question is on 2.4 GHz ISM band, the 2.4 GHz ISM band is bound by 2.4000 GHz and 2.5000 GHz (2.45000 GHz + or - 50 MHz), as defined by the FCC. Of the 100 MHz between 2.4000 GHz and 2.5000 GHz, only the frequencies 2.4000 - 2.4835 GHz are actually used by wireless LAN devices.

Conclusion: FCC has defined 100 MHz (2.4000 GHz - 2.5000 GHz) even though the wireless LAN devices only use 83.5 MHz (2.4000 GHz - 2.4835 GHz).

Regarding the question on Lower UNII band, the lower band is bound by 5.15 GHz and 5.25 GHz and is specified by the FCC to have a maximum output power of 50 mW. When implemeting 802.11a compliant devices, the IEEE has specified 40 mW (80%) as the maximum output power for 802.11a compliant radios reserving the lower band for indoor operation only.

Conclusion: FCC defines 50 mW and IEEE specifies 40 mW.

I hope that helps.