2 Avoiding Hazards
23
Peak power density in the far field of a radio frequency point source is calculated as follows:
S = power density in W/m
2
P= Maximum Average transmit power capability of the radio, in W
G= total Tx gain as a factor, converted from dB
d = distance from point source, in m
Where
2
4
.
d
GP
S
π
=
Rearranging terms to solve for distance yields:
S
GP
d
.4
.
π
=
2.1.1.1 Calculated Distances and Power Compliance Margins
Table 3 shows calculated minimum separation distances d, recommended distances and
resulting power compliance margins for each frequency band and antenna combination.
Variable Band Antenna Max
Average
Transmit
Power in
Burst
(Watt)
P
(Watt)
G S
(W/m
2
)
d
(m)
Recom-
mended
Distance
(m)
Power
Compliance
Margin
Integrated
0.005
(7dBm)
0.00250
200
(23dBi)
10 0.06
5.4
GHz
External
4ft Dish
0.00035
(-4.6dBm)
0.00017
2884
(34.6dBi)
10 0.06
1 15.9
Integrated
0.020
(13dBm)
0.01
200
(23dBi)
10 0.13 1 7.6
EU
5.8
GHz
External
4ft Dish
0.0014
(-1.4dBm)
0.0007
2884
(34.6dBi)
10 0.13 1 7.6
Integrated
0.32
(25dBm)
0.16
200
(23dBi)
10 0.5 2 4.0
External
2ft Flat
Plate
0.32
(25dBm) 0.16
631
(28dBi) 10 0.9 4 4.5
FCC
5.8
GHz
External
6ft Dish
0.32
(25dBm)
0.16
6310
(38dbi)
10 2.83 10 3.5
Table 3 - Power Compliance Margins
Notes:
• The regulations require that the power used for the calculations is the maximum power in
the transmit burst subject to allowance for source-based time-averaging.
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