Baldur Norddahl baldur.norddahl at gmail.com
Wed Apr 22 20:51:29 UTC 2015

First: buy a power meter. They are really cheap and the only way to know
for sure how much signal you got. It will also tell you how much launch
power you have. The fiberstore modules are listed as 0 to +5 dBm launch
power - if you got lucky it might be +5 and if you got a lower end module
it might be close to 0. Obviously this makes a huge difference for how much
power you get on the other end. Also it is said that the laser will lose
power over time.

Second you need to think in terms of power budget, not distance. So you got
68 km and the module is rated for 80 km - but not all fiber is not born
equal. A power meter allows you to measure the true link loss.

Third you did not tell what DWDM multiplexer you are using. A 44 channel
DWDM multiplexer from Fiberstore can have up to 4.5 dB insertion loss. You
might have two of those on your link for a total of 9 dB loss. Your 80 km
module has a 23 dB link budget, so this leaves you with 23-9 = 14 dB
budget. If your fiber has 0.25 dB loss per km, that is only 56 km.



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