User's Manual

PMP 400/430 and PTP 200 Series Canopy User Guide
Supplement
Issue 4 0 – DRAFT 6 November 2009 Page 61 of 64
Guidelines for Limiting Exposure to Time-Varying Electric, Magnetic, and
Electromagnetic Fields.
The applicable power density exposure limits from the documents referenced above are
• 10 W/m
2
for RF energy in the 5.4-GHz frequency bands.
Peak power density in the far field of a radio frequency point source is calculated as follows:
S =
P⋅ G
4
π d
2
where
S = power density in W/m
2
P = RMS 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
Rearranging terms to solve for distance yields
d =
P⋅ G
4
π S
Table 16 shows calculated minimum separation distances d, recommended distances and
resulting power compliance margins for each frequency band and antenna combination.
Table 16: Calculated Exposure Distances and Power Compliance Margins
Frequency
Band
Antenna
Variable
d
(calcu-
lated)
Recom-
mended
Separation
Distance
Power
Compliance
Margin
P
G
S
5.4 / 5.8
GHz OFDM
Integrated,
17 dBi
0.05 W
(10 dBm)
50
(17 dB)
10
W/m
2
6 cm 20 cm
(8 in)
10
Connectori
zed, 17 dBi
0.05 W
(10 dBm)
50
(17 dB)
10
W/m
2
6 cm 20 cm
(8 in)
10
4.9 GHz
OFDM
Integrated,
17 dBi
0.063 W
(18 dBm)
40
(16 dB)
10
W/m
2
14 cm 20 cm
(8 in)
2
Connectori
zed, 17 dBi
0.063 W
(18 dBm)
40
(16 dB)
10
W/m
2
14 cm 20 cm
(8 in)
2
The “Recommended Distances” are chosen to give significant compliance margin in all cases.
They are also chosen so that an OFDM module has the same exposure distance as a Canopy
module, to simplify communicating and heeding exposure distances in the field.
These are conservative distances:
• They are along the beam direction (the direction of greatest energy). Exposure to the
sides and back of the module will be significantly less.
• They meet sustained exposure limits for the general population (not just short term
occupational exposure limits), with considerable margin.