Wi Lan Inc EB03 Manuale Utente

Link Budget Example

JUL 2001 Rev 03

119

The values for cable and connector losses in this example are only for illustration. You will need to work these 
out for your specific installations.

System Gain + Antenna Gain 

≥ Propagation Loss + Desired Fade Margin + 

Cable Losses + Connector Losses

or

Actual Fade Margin 

≥ System Gain + Antenna Gain – Propagation Loss 

– Cable Losses – Connector Losses
and
Actual Fade Margin 

≥ Desired Fade Margin

where:

System Gain = Tx Power – Rx Sensitivity
Antenna Gains = Tx Antenna Gain + Rx Antenna Gain
Cable Losses = Base Cable Losses + Remote Cable Losses
Connector Losses = Base System Connector Losses + Remote System 
Connector Losses

Desired Fade Margin = 15 dB
Tx Power = 20 dBm
Rx Sensitivity = –81 dBm
Tx Antenna Gain = 21 dBi
Rx Antenna Gain = 21 dBi
Propagation Loss for desired range of 10km = 100 + 20 x log(10) = 120 dB
Tx Cable Losses (5m LMR400) = 5 * 0.22 = 1.1 dB
Rx Cable Losses (5m LMR 400)= 5 * 0.22 = 1.1 dB
Tx Connector Losses = 1 dB
Rx Connector Losses = 1 dB

System Gain = 20 - (-81) = 101 dB
Antenna Gains = 21 + 21 = 42 dBi
Cable Losses = 1.1 + 1.1 = 2.2 dB
Connector Losses = 1 + 1 = 2 dB

Actual Fade Margin = 101 + 42 – 120 – 2.2 – 2 = 18.8 dB

A goal of Actual Fade Margin 

≥ 15 dB is achieved.