User's Manual

Appendix A. Radio Signal Propagation
BreezeNET BU-DS.11/RB-DS.11 A-7 User’s Guide
Example:
Link Parameters:
Frequency: 2.4 Ghz
P
out
= 4 dBm (2.5 mW)
Tx and Rx cable length (Ct and Cr) = 10 m. cable type RG214 (0.6 dB/meter)
Tx and Rx antenna gain (Gt and Gr) = 18 dBi
Distance between sites = 3 Km
Receiver sensitivity (Ps) = -84 dBm
Link Budget Calculation
EIRP = P
out
- Ct + Gt = 16 dBm
Pl = 32.4 + 20xLog(FMhz) + 20xLog(RKm) ≅ 110 dB
Si = EIRP - Pl + Gr - Cr = -82 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.