Path: utzoo!utgpu!water!watmath!clyde!rutgers!rochester!bbn!uwmcsd1!ig!agate!saturn!eshop
From: eshop@saturn.ucsc.edu (Jim Warner)
Newsgroups: comp.dcom.lans
Subject: Re: Info. needed on fiber specs for FDDI use
Keywords: FDDI fiber optics
Message-ID: <1831@saturn.ucsc.edu>
Date: 4 Feb 88 21:32:09 GMT
References: <1591@aecom.YU.EDU>
Reply-To: eshop@saturn.ucsc.edu (Jim Warner)
Organization: University of California, Santa Cruz; CIS/CE
Lines: 20

In article <1591@aecom.YU.EDU> glen@aecom.YU.EDU (Glen M. Marianko) writes:
>
>	Fiber Cable: 62.5/125 Multimode Graded Index
>	Capacity:    200-500 MHz per kilometer
>	dB Loss:     1.8dB per kilometer maximum
>	Connectors:  SMA 905/ST/Amphenol Duplex
>
>My greatest concern is this 200-500 MHz rating.  What does it mean,
>exactly?  ....

It isn't "MHz per kilometer".  That would imply that the longer
cable runs have greater bandwidth.  It's "MHz-kilometer".  You
divide this number by the length of your cable to find the bandwidth
of the fiber segment.  You can write the spec as 200 MHz-Km or greater.
The actual signalling rate on a 100 MHz FDDI ring is 125 MHz.  But
a 3000 ft run is less than 1 KM so a 200 MHz-KM cable will have
adequate bandwidth.  

"dB per kilometer" is correct.  The "dB" is a measure of signal
amplitude loss, and the longer the cable, the greater the loss.