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Spectral mask
The spectral mask for the 802.11b standard is shown in the following figure:
f
c
Available channels
An important concept regarding channel assignments is that the channel actually represents the centre
frequency that the transceiver within the radio and access point uses (for example 2.412 GHz for channel 1
and 2.417 GHz for channel 2). There is only 5 MHz separation between the centre frequencies, and an 802.11b
signal occupies approximately 30 MHz of the frequency spectrum. The signal falls within about 15 MHz of
each side of the centre frequency. As a result, an 802.11b signal overlaps with several adjacent channel
frequencies. You can tell that, despite there being eleven channels allocated (for the United States), there are
actually only three non-overlapping channels: 1, 6, and 11.
Maximum power output
The maximum power output for the 802.11b standard is 100 mW.
However, keep in mind that an improper combination of power level and antenna gain can result in
Equivalent Isotropic Radiated Power (EIRP) above the amount allowed per regulatory domain. The following
table indicates the maximum power levels and antenna gains allowed for each IEEE 802.11b regulatory
domain.
Regulatory Domain
America
(4 W EIRP maximum)
20
-30
f
-20
f
f
c
c
c
-
-
11
9
Antenna Gain (dBi)
2.2
5.2
6
8.5
12
13.5
0 dBr
-30 dBr
-50 dBr
f
f
f
f
+20
c
c
c
c
+
+
9
11
Maximum Power Level (mW)
100
100
100
100
100
100
Chapter 2
802.11 Standards
f
+30
MHz
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E-DOC-CTC-20060609-0001 v2.0
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