HP 200 Series Services And Applications page 245

To calculate the cable loss between two adjoining stations, use the formula
shown below:
Attenuation = (Cable Len (km) x Attenuation/km) +
(Splices x Attenuation per Splice) +
(Connectors x Connector Attenuation) +
(Loss at Transmit MIC)
For example:
2 km fiber x 2.5 dB/km
2 splices x 0.25 dB/splice
1 connector x 0.5 dB/connector 0.5 dB
Loss at transmit MIC
Total link attenuation
Once you know the attenuation, you can calculate the remaining power
available for the network. The maximum allowed loss is 11 dB. The formula
is shown below:
Power Available = Optical Power Budget – Attenuation
For example:
Optical power budget
Attenuation
Total available
After calculating the dB loss of a particular link, it is important to compare
the resulting power with receiver sensitivity. If the receiver is not sensitive
enough, poor link quality will result.
Optical Transmitters and Receivers
Transmitters convert data from electrical signals to light. The receiver
converts the light signals back to electrical signals. Receivers contain photo
detectors that convert incoming optical signals back into electrical signals.
Optical transmitters convert modulated electrical signals into modulated
light signals that are transmitted through the fiber-optic cable. In multimode
fiber cable, transmitters are light-emitting diodes (LEDs) that convert
electrical signals into light signals. In single-mode fiber cable, transmitters
are laser-quality light-emitting diodes or laser diodes (LDs).
Shining a Light on FDDI
5.0 dB
0.5 dB
+0.5 dB
6.5 dB
11 dB
– 6.5 dB
4.5 dB
How FDDI Works
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