User's Manual

Appendix
BreezeNET PRO.11 Series 8-18 User’s Guide
Link Budget Calculation
EIRP = P
out
- Ct + Gt = 31.6 dBm
L = 36.5 + 20xLog(F
Mhz
) + 20xLog(D
Mile
) ≅ 118 dB
Pr = EIRP - L + Gr - Cr = -72 dBm
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 9.11: 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.)