User's Manual

Intelibs, Inc. Proprietary and Confidential Page 43
43
6 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 RHU 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.
RU 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 identified 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 10foot high, an average person is assumed 6foot high, the
distance from antenna to body is 4 feet (112 cm).
For PCS 1900 band, the maximum power output per carrier is assumed 20dBm. With the assumption of
13dBi antenna gain is used, PG in the equation is equal to 33dBm EIRP.
Using S = PG/4pieR^2
S = 2/(4*3.14)*112^2 = 12.7μW/cm^2
Also worst case with the assumption of minimum distance of 20 cm according to FCC regulation:
S = 2/(4*3.14)*20^2 = 0.4mW/cm^2