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APPENDIX D: Radio Signal Propagation
In conclusion, the received signal power is above the sensitivity threshold, so the
link should work. The problem is that there is only a 2-dB difference between
received signal power and sensitivity. Normally, a higher margin is desirable
because of fluctuation in received power as a result of signal fading.
S
IGNAL
F
ADING
Fading of the RF signal is caused by several factors:
•
Multipath
The transmitted signal arrives at the receiver from different directions, with
different path lengths, attenuation, and delays. The summed signal at the
receiver may result in an attenuated signal.
Figure D-6. Multipath Reception.
•
Bad Line of Sight
An optical line of sight exists if you can see one antenna from the other—there
are no obstructions between them.
Radio-wave clear line of sight exists if a certain area around the optical line of
sight (Fresnel zone—see the next page) is clear of obstacles. A bad line of sight
exists if the first Fresnel zone is obscured.
•
Link Budget Calculations
•
Weather conditions (Rain, wind, etc.)
At high rain intensity (150 mm/hr), the fading of an RF signal at 2.4 GHz may
reach a maximum of 0.02 dB/km.
Wind may cause fading due to antenna motion.
Transmitter
Receiver
Multipath
reception
Summary of Contents for LW0050A
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