User Manual

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Understanding Industrial WLAN – IEEE 802.11
UNII Band
The 5 GHz UNII band consists of 3 parts, each 100 MHz wide. The 802.11a standard uses this band. Each
part of the UNII band includes 4 non-overlapping channels with 5 MHz of guard band between them. The
FCC states that the lower band (UNII-1) can only be used indoors, the middle band (UNII-2) can be used
indoors or outdoors, and the higher band (UNII-3) should only be used outdoors. Since UNII-1 and UNII-2
can be used indoors, the maximum number of non-overlapping channels in an indoor environment is 8. See
below for channels supported in the 5 GHz UNII band for different countries.
Channel ID Frequency (MHz) USA EU, M. East, Asia Japan
36 5180 V V V
40 5200 V V V
44 5220 V V V
48 5240 V V V
52 5260 V V V
56 5280 V V V
60 5300 V V V
64 5320 V V V
100 5500 V V V
104 5520 V V V
108 5540 V V V
112 5560 V V V
116 5580 V V V
120 5600 V V V
124 5620 V V V
128 5640 V V V
132 5660 V V V
136 5680 V V V
140 5700 V V V
149 5745 V
153 5765 V
157 5785 V
161 5805 V
165 5825 V
Signal Power
Radio signals are transmitted with a certain power level. Power is measured in watts. However, a watt is a
rather large amount of power in WLAN. Therefore, power is usually measured in milliwatts (mW), which is one-
thousandth of a watt. A typical wireless AP transmits between 30 to 100 mW of power, and about 50 mW for
wireless adaptors (clients). Certain applications will require higher transmit (Tx) power and may attempt to use
power boosters or customized high power modules to amplify the transmit power. However, such attempts
may cause the system to exceed the radio emission regulations (i.e., FCC regulations) of one’s country so take
caution during high power operation.
dB, dBm, dBi
Power measured in mW is hard on the math when we are dealing with extremely small power levels at the
receiver end. Therefore, instead of using absolute values (milliwatts) we often convert them into dBm. The
unit of dBm is a logarithmic representation of mW. The conversions are as follows: