MPE calculations

FCC ID: MTF09000

RF Exposure Info

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FCCID_136582

RF Exposure Requirements

The EUT is considered as a mobile device. Therefore the Electromagnetic Field Strength
(E) was calculated and compared with FCC Maximum Permissive Exposure (MPE) limit.
The Power Density (S) can be calculated using the formula

S = (30 × EIRP) / (120 × π) / D2 (W/m2)

The maximum EIRP in dBm equal P + G −cl= 35.6 + 5 −2=38.6 dBm or 7.24 W.

Therefore, S = 0.576/ D2 (W/m2)

The Duty Cycle can be taking into account.

S = 0.576 × DC/ D
2

According Microburst protocol, the worst case of Duty Cycle (DC) is 16.7%, (e.g. the
transmitter in ON for 3 s, and OFF for 15 s). However, in practice in back-up mode, once
an hour the resulting transmitter DC would be approximately 0.08%.

In the Table below is shown the MPE calculated data for different distances, for
DC=0.167, DC=0.0008, and the FCC Limit, which for uncontrolled environment equal
2 2
F/1500 (mW/cm ) or F/150 (W/m ) where F is a frequency in MHz.

F=836.5 MHz
Distance. m Calculated S, W/ m2 Calculated S, W/ m2 MPE Limit W/ m2
DC=0.167 DC=0.0008
0.1 9.62 0.046 5.58
0.2 2.40 0.012 5.58
0.3 1.07 0.005 5.58
0.4 0.60 0.003 5.58
0.5 0.38 0.002 5.58

For a 16.7% Duty Cycle the power density at a distance of 0.2 meters is 3.6 dB below the
MPE limit. Therefore, to comply with MPE requirements, the maximum permissible
antenna gain shall not exceed 8.6 dBi.

In actual usage environment in backup mode as justified by customer the duty cycle
would be approximately 0.08%. The calculated Power density is 0.012 W/ m2. This is
2
26.7 dB below the MPE limit of 5.58 W/ m . The maximum permissible antenna gain
shall be 31.7 dBi.

Document Created: 2001-02-15 14:31:26
Document Modified: 2001-02-15 14:31:26

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