dB Loss Calc

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Equation / Last modified by KurtHeckman on 2017/08/01 14:38
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The dB Loss calculator computes the dB loss over a distance (L) including nominal rate of loss per kilometer (LL) and losses associated with any number of step downs in two types of loss sources (e.g. relays, connectors or splices).

INSTRUCTIONS:  Choose your preferred units and enter the following:

  • (L) This is the transmission length.
  • (LL) This is the dB loss per kilometer in the natural medium of transmission (e.g. fiber optic cable, atmosphere)
  • (LS1) This is the dB loss introduced by every occurrence of this type of object in the transmission line.
  • (nLS1) This is the number of type one objects in the transmission line.
  • (LS2) This is the dB loss introduced by every occurrence of this type of object in the transmission line.
  • (nLS2) This is the number of type two objects in the transmission line.

dB Loss: The calculator returns the transmission loss in dB.  

The Math / Science

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To test a fiber optic cable plant, you need to perform a loss test.   The loss across a fiber-optic line is a function of the loss in the fiber optic cable itself and the loss introduced by multiple loss sources including connectors and splices. 

The typical mated connector pair loses 0.75 dB for each connector.    A splice typically introduces 0.3 dB loss. 

The loss for different types of fiber cable is as follows:

  • 1550 nm singlemode fiber loses 0.4 dB every kilometer.
  • 1310 nm singlemode fiber loses 0.5 dB every kilometer.
  • 1300 nm multimode fiber loses 1.0 dB every kilometer.
  • 850 nm multimode fiber loses 3.0 dB every kilometer.

The above attenuation profile is available in a simplified dB Loss calculator, the Cable Loss Budget calculator.  The Cable Loss Budget calculator lets you enter the length of the cable run, number of connectors, the loss per connector, the number of splices and the loss per splice.  It returns the Cable Loss Budget in dBs.