User's Manual

Link Budget Example
JUL 2001 Rev 03
119
Link Budget Example
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.
Formulas: 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
Variables: 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
Variable
Calculations:
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
Calculation:
Actual Fade Margin = 101 + 42 – 120 – 2.2 – 2 = 18.8 dB
Analysis: A goal of Actual Fade Margin ≥ 15 dB is achieved.