User's Manual

Intelibs, Inc Proprietary and Confidential Page 37
37
4 Human RF Exposure – Maximum Permissible Exposure Evaluation
The recent FCC developed guideline for evaluation of the human exposure to the RF emissions. The
maximum permission Exposure (MPE) for power density of the transmitter operating RF ranges between
300 KHz and 100 GHz. As the Intelibs SRU belongs to the fixed equipment, Analysis has been conducted
to evaluate the MPE from the distance greater than 20 Cm as the fixed equipment required.
Antenna gain is restricted to 1.5W ERP (2.49 W EIRP) in order to satisfy RF exposure compliance
requirements. If higher than 1.5W ERP, routing MPE evaluation is needed. The antenna should be
installed to provide at least 20 cm from all persons to satisfy MPE requirements of FCC Part 2, 2, 1091.
SRU transmits far below that FCC power density restricts. FCC defines power output limits at 20 cm
distance for various frequency ranges:
• Over 300 MHz to 1.5 GHz the limit is determined by frequency /1500
• Above 1.5 GHz the limit is 1 mW/cm^2
The basic equation for determining power density is:
S = PG/4(pie)R^2
Were S is power density, which is mW/Cm^2
PG, the transmitted power from the antenna indentified as EIRP (Equivalent Isotropically Radiated
Power)
R is the distance of interest from the antenna.
Typical Installation Example:
As the typical height of a floor is assumed as 10 foot high, an average person is assumed 6 foot high, the
distance from antenna to body is 4 feet (112 cm).
For PCS 1900 band, the maximum power output per carrier is assumed 23 dBm. With the assumption of
5 dBi antenna is used, PG in the equation is equal to 28 dBm EIRP.
Using S = PG/4pieR^2
S = 0.63/(4*3.14)*112^2 = 4μW
Also worst case with the assumption of minimum distance of 20 cm according to FCC regulation:
S = 0.63/(4*3.14)*20^2 = 0.1mW