Technical data

52 Theoretical and general applications www.westermo.com
Loss Budget Calculation
The communication range of a system is dependent on the transmission output, the
sensitivity of the receiver and the loss that arises in terminations and cable splices. In
order to calculate this range a fibre budget is stated, which is the difference between
the transmitter output power and receiver sensitivity, both these values have a typical
value and a minimum level. We have chosen to document both these values for most
products. We do this because there can be large variations in the manufacturers’ spe-
cifications; this applies mainly to singlemode fibre.
Example
We connect two devices together using two MD-62s. Should we use multimode or
singlemode fibre? Multimode cable has an attenuation of 3.2 dB/km at 820 nm whilst
singlemode has an attenuation 0.5 dB/km at 1300 nm. The range in our example is
6 km (3.72 mi) with two splices in the cable, which both give an attenuation of 0.2 dB.
Option 1, Multimode cable
3.2 dB/km x 6 + 2 x 0.2 dB = 19.6 dB
Option 2, Singlemode cable
0.5 dB/km x 6 + 2 x 0.2 dB = 3.4 dB
According to the manual for the MD-62 the minimum fibre budget for:
Multimode cable 62.5/125 with a wave length of 820 nm 14.5 dB
Singlemode cable 9/125 with a wave length of 1300 nm 6.3 dB
In this example singlemode should be chosen.
This is an example of how the fibre budget is used to calculate the transmission
distance, in our example we know the fibre budget from the manual for MD-62
B A C K