User's Guide

Appendix A. Radio Signal Propagation
BreezeNET BU-DS.11/RB-DS.11 A-7 User’s Guide
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 due to fluctuation in received power as a result of signal
fading.
Signal Fading
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 A-6. Multipath Reception
Bad Line of Sight
An optical line of sight exists if an imaginary straight line can connect the antennas on either side of
the link.
Radio wave clear line of sight exists if a certain area around the optical line of sight (Fresnel zone)
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.
• Interference
Interference may be caused by another system on the same frequency range, external noise, or some
other co-located system.
The Line of Sight Concept
An optical line of sight exists if an imaginary straight line can be drawn connecting the antennas on
either side of the link.