Motorola VSWR, Service Manual Supplement

Page: 16 / 44

Human exposure to radio frequency energy (PCS1900 only)
5th Feb 99
8
Service Manual Supplement: VSWR Monitor for M-Cell 6
68P02900W86-O
Example
calculation
For a base station with the following characteristics, what is the minimum distance from
the antenna necessary to meet the requirements of an uncontrolled environment?
Transmit frequency 1930MHz
Base station cabinet output power, P +39.0 dBm (8 watts)
Antenna feeder cable loss, CL 2.0 dB
Antenna input power P in P–CL = +39.0–2.0 = +37.0 dB (5 watts)
Antenna gain, G 16.4 dBi (43.65)
Using the following relationship:
G +
4 p r
2
W
Pin
Where
W is the maximum permissible power density in W/m
2
and
r is the safe distance
from the antenna in metres, the desired distance can be calculated as follows:
r +
GPin
4 p W
Ǹ
+
43.65 5
4 p 12.87
Ǹ
+ 1.16 m
where W = 12.87 W/m
2
was obtained from table listed above and converting from
mW/cm
2
to W/m
2
.
The above result applies only in the direction of maximum radiation of the
antenna. Actual installations may employ antennas that have defined radiation
patterns and gains that differ from the example set forth above. The distances
calculated can vary depending on the actual antenna pattern and gain.
NOTE
Power density
measurements
While installation calculations such as the above are useful and essential in planning and
design, validation that the operating facility using this equipment actually complies will
require making power density measurements. For information on measuring RF fields for
determining compliance with ANSI IEEE C95.1-1991, see
IEEE Recommended Practice
for the Measure of Potentially Hazardous Electromagnetic Fields - RF and Microwave,
IEEE Std C95.3-1991. Copies of IEEE C95.1-1991 and IEEE C95.3-1991 may be
purchased from the Institute of Electrical and Electronics Engineers, Inc., Attn:
Publication Sales, 445 Hoes Lane, P.O. Box 1331, Piscattaway, NJ 08855-1331,
(800) 678-IEEE or from ANSI, (212) 642-4900. Persons responsible for installation of this
equipment are urged to consult these standards in determining whether a given
installation complies with the applicable limits.
Other equipment
Whether a given installation meets ANSI standards for human exposure to radio
frequency radiation may depend not only on this equipment but also on whether the
environments being assessed are being affected by radio frequency fields from other
equipment, the effects of which may add to the level of exposure. Accordingly, the overall
exposure may be affected by radio frequency generating facilities that exist at the time
the licensee’s equipment is being installed or even by equipment installed later.
Therefore, the effects of any such facilities must be considered in site selection and in
determining whether a particular installation meets the FCC requirements.