Fiber Optic Loss Calculations

[tom baker]

I am new to fiber optic and have a short length of single mode to light using N-Tron 300 series media convertors.
Fiber length is .5 km, with attenuation of .35 dB/Km
6 splices at .3 dB loss
2 connections at 1 dB loss
Total Loss is 4dB
At 1310 nm, N Tron specs are:
TX Power Min/Max -19/-14 dBm
RX sensitivity Max -32 dB
Max power (-14) – Rx sensitivity max (-32) is 18 dB.
18 dB – loss (4 db) = 14 dB
So do I need to use a 14 dB pad?

 

[GrayHair]

Since there are no other replies, I'll jump in. I dug out my stuff from training and found a note saying to shoot for the midrange of a receiver's sensitivity (trainer was a factory rep so that could be brand specific). Seems to make sense.

According to the manual I found online, the power and sensitivity figures you listed are for multi mode, but your post stated single mode. Maybe I misread something.

Hope this is of some help. Wasn't that long after we started using single mode that I decided to retire and didn't get to work with single mode much.

 

[low-wattage]

Here's how I am reading that, minimum power = -19; receive sensitivity = -32; maximum link loss = -32 - (-19) = -13dB

So you'd be well under at a budgeted 4db, if the link performs as expected - you'd have to test it with a light source of the same wavelength and meter to really know the loss of the link.

I think with the calculation you're doing, a 14dB pad would take it right to the limit of the receive sensitivity, you don't wan't that.

With media adapters that use a standard protocol for ethernet over fiber - 100BaseFX, 1000BaseLX, 1000baseSX, etc. - you'll have a maximum distance and a maxiumum loss specified in the standard, as well as the wavelength, and the type of fiber you can use.

http://www.hca.hitachi-cable.com/pdfs/fiber-distances-by-application.pdf

I think all of the standard ones have no minimum loss, so you'd never need to use a pad - you could connect them with a 3' patch cord. (Done so many times to test the equipment.) In fact most of the non-standard ones I have used don't have a minimum either, but I wouldn't be surprised if some of the extremely long distance hardware telcos and ISPs had a minimum.

If you're using a media adapter made for multimode, it probably won't work with singlemode. What's the model number on yours?