User Manual

iSTRATA TX Operator’s Guide/Tech Ref Manual
Note To User - RF Exposure
MPE Calculation
RF Exposure
Microwave Radio Communications (MRC) provides this warning
for safety purposes with the intent to inform the user of the
potential hazard to RF exposure. The following guidelines for
safe operation were derived from OET bulletin 65, August 1997,
as recommended by the Federal Communications Commission
(FCC).
The 6.4 - 7.125 GHz STRATA transmitter is a mobile transmitter
designed to provide services to broadcast ENG users under
CFR 74 subpart F and 74.601 TV pickup stations. This unit,
operated without an antenna, will not create RF energy
exceeding 1.0 mW/cm
2
, the FCC limit for exposure. Once
connected to an antenna, the potential for harmful exposure will
be greatly enhanced.
In this situation, a certain distance from the radiator is to be
maintained. Calculations need to be performed to understand
what that safe margin for exposure is. This is known as the
Maximum Permissible Exposure (MPE) limit.
Calculations provided are for common antennas often utilized in
the ENG environment. The following formula used is that
suggested by OET 65.
Calculating MPE
EIRP = P * (10 ^ (G / 10)) = (antilog of G/10) * P
P = RF power delivered to the antenna in mW
G = Power gain of the antenna in the direction of interest relative
to an isotropic radiator
R = distance to the center of radiation of the antenna in
centimeters
S = MPE in mW/cm² (milliwatts per square centimeters)
Conversions
dBi to numeric gain = Antilog (dBi/10)
Feet to centimeters = Feet * 30.48
Centimeters to Feet = cm * .0328
4 π = 12.57
User Input
RF power delivered to the antenna = Watts
Antenna gain (referenced to isotropic antenna) = dBi
Distance from the center of radiation = Feet
Calculation steps:
1. [P] RF power input. Convert watts to milliwatts = Watts *
1000
2. [G] Antenna gain dBi. Convert to numeric gain = Antilog
(dBi/10)
3. [EIRP] Multiply P * G
4. [R] Convert centimeters to feet = Centimeters * .0328
5. Square R
PG (or EIRP)
S=
4πR
2