Link Budget is the calculation of all gains and lossess from the transmitter through the medium (free space, cable, waveguide etc.) to a receiver in microwave telecommunication for line of sight radio system. It calculates the attenuation of transmitted signal due to propagation, antenna gains and other loses. Randomly, varying gains channel such as fading are taken into calculation by adding some margin depending on the anticipated severity effects. The margin required can be reduce by using mitigation techniques such as antenna diversity.
The Link Budget simple calculation looks like this :
Received Level (dBm) = Transmitted Power (dBm) + Lossess + Antenna Gains
Logarithmically Expressed by this equation :
Rx Level = Tx Parameter + Free Space Loss + Rx Parameter
Or ;
RxL = [TxP + GTx + TxLs] + FsLs + [GRx + RxLs]
Where :
RxL = Received Level (dBm)
TxP = Transmitter Power (dBm)
GTx = Transmitter antenna gain (dBi)
TxLs = Transmitter Loss (dB)
FsLs = Free Space Loss (dB)
GRx = Receiver antenna gain (dBi)
RxLs = Receiver Loss (dB)
Where Free Space Loss is a constant calculate by :
Free Space Loss (dBm) = - [92.4+20Log(f)+20Log(D)]
f = frequency used by transmitter (MHz)
D = distance between antenna station (m)
Example of a simple system :
The Path Calculation or Link Budget between Station AA and Station BB with frequency 13 GHz for middle distance radio microwave link, using 1+0 ODU configuration that eliminates wave guide loss at the both station.