Terrain And Signal Strength - CalAmp Guardian-100 User Manual

Table 2.2 – RF Exposure Compliance Minimum Safety Distances
Min Safety Distance
(VHF @ max power)
Min Safety Distance
(UHF @ max power)
Min Safety Distance
(900 MHz @ max power)
Note: It is the responsibility of the user to guarantee compliance with the FCC
MPE regulations when operating this device in a way other than described above.
The Guardian radio uses a low power radio frequency transmitter. The concentrated energy
from an antenna may pose a health hazard. People should not be in front
of the antenna when the transmitter is operating.
RF Exposure
The installer of this equipment must ensure the antenna is located or pointed such that it
does not emit an RF field in excess of Health Canada limits for the general population.
Recommended safety guidelines for the human exposure to radio frequency electromagnetic
energy are contained in the Canadian Safety Code 6 (available from Health Canada) and the
Federal Communications Commission (FCC) Bulletin 65.
Any changes or modifications not expressly approved by the party responsible for
compliance (in the country where used) could void the user's authority to operate the
equipment.
2.6

TERRAIN AND SIGNAL STRENGTH

A line of sight path between stations is highly desirable and provides the most reliable
communications link in all cases. A line of sight path can often be achieved by mounting
each station antenna on a tower or other elevated structure that raises it high enough to
clear surrounding terrain and other obstructions.
The requirement for a clear transmission path depends on the distance to be covered by the
system. If the system is to cover a limited distance, say 3-5 miles, then some obstructions
in the transmission path may be tolerable. For longer-range systems, any obstruction could
compromise the performance of the system, or block transmission entirely.
The signal strength (RSSI) at the receiver must exceed the receiver sensitivity by an
amount known as the fade margin to provide reliable operation under various conditions.
Fade margin (expressed in dB) is the maximum tolerable reduction in received signal
strength, which still provides an acceptable signal quality. This compensates for reduced
signal strength due to multi-path, slight antenna movement or changing atmospheric
losses. CalAmp recommends a 30 dB fade margin for most projects. Table 2.3 shows the
RSSI versus Reliability.
001-5006-000_FCC.docx
Antenna Gain
5 dBi 10 dBi
123cm 218.8cm
105.7cm 188cm
63.8cm 115 cm
15 dBi
389cm
334.4cm
201.7 cm
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