What Loss Should You Get When Testing Cables?

Before testing, preferable during the design phase, you should calculate a loss budget for the cable plant to be tested to understand the expected measurement results. Besides proviiding reference loss values to test against, it will confirm that the network transmission equipment will work properly on this cable. While it is difficult to generalize, here are some guidelines:

-For each connector, figure 0.3-0.5 dB loss for adhsive/polish connectors, 0.75 for prepolished/splice connectors (0.75 max from TIA-568)
-For each splice, figure 0.2 dB
-For multimode fiber, the loss is about 3 dB per km for 850 nm sources, 1 dB per km for 1300 nm. This roughly translates into a loss of 0.1 dB per 100 feet for 850 nm, 0.1 dB per 300 feet for 1300 nm.
-For singlemode fiber, the loss is about 0.5 dB per km for 1300 nm sources, 0.4 dB per km for 1550 nm. This roughly translates into a loss of 0.1 dB per 600 feet for 1300 nm, 0.1 dB per 750 feet for 1300 nm.
So for the loss of a cable plant, calculate the approximate loss as:
(0.5 dB X # connectors) + (0.2 dB x # splices) + fiber loss on the total length of cable

December 21, 2011

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