Radiance CWDM System 19
Calculating the Maximum Link Distance
After you have determined the power budget for a fiber link, you can use that
value to calculate the maximum distance the link will support.
Power Budget - Buffer
Distance =
_________________________________
[EQ. 3]
Fiber Attenuation
Typically, a buffer of 2 dBm is subtracted from the power budget to account for
other factors that may affect the loss of transmission power. These factors
include fiber aging, temperature, humidity, poor splices, etc.
Fiber attenuation is the loss of signal strength as it travels through the fiber. The
attenuation varies with the wavelength. Refer to the specifications of the fiber
cable you are using, to obtain the fiber attenuation value. Typical values are 0.2
to 0.35 dBm/km.
Example 4: Calculate the maximum link distance for Link A from Example 2.
Using a worst case value of 0.35 for the fiber attenuation, the distance is:
18 dBm - 2 dBm
Distance =
_____________________________
= 46 km
0.35 dBm/km
Example 5: Calculate the maximum link distance for Link B from Example 3.
Using a worst case value of 0.35 for the fiber attenuation, the distance is:
22 dBm - 2 dBm
Distance =
_____________________________
= 57 km
0.35 dBm/km
