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Re: Fiber Optic Information



"Sort of", there are now LED's for launching into SM and always have been 
lasers for launching into MM, however distance and bandwidth are limited 
with LED's for SM, and cost/over powering the MM for Lasers.  I'm using 
much too simplistic terms for the true technology but this will work in 
this description.  An example is with Gigabit ethernet where in order to 
get the proper bandwidth distance factor on MM (to get it out to 100 Meters 
for horizontal usage) many have successfully "cheated" by setting the modes 
on the cable by launching into a SM segment spliced to a MM cable then 
spliced again to a SM segment at the distant end.  (the Segment is 2-5 
meters long, the MM Cable is 90+meters long).  The biggest challenge with 
SM is since the aperture is so small properly terminating it with 
connectors and polishing it is better left up to commercial entities 
especially if any level of power is being used on the fiber requiring use 
of "angle polish or ultra polish connectors".

Generally speaking, analog use of fiber requires SM for Bandwidth above 
150MHz, or distance over 2000 foot (this is that distance bandwidth 
factor!) and for digital SM for datarates over OC-3 (155MBPS).  Again this 
is gross generallizations, short runs of MM will carry large bandwidths and 
very high data rates, SM shines in long distances and ultra high 
bandwidths, (in fact they have not been able to max out the bandwidth and 
they are in the TeraHertz and still feel there is plenty of room over 60 
Kmeters+, and lets not get into the extreme bandwidths offered by DWDM 
(essentially color multiplexing).)

Bob

Oh by the way some of my credentials are Certified Fiber Optic Tech, BICSI 
RCDD, and having been Senior engineer in Corporate technology lab doing 
some DWDM beta testing for a couple of manufacturers.

I have kept this info very simplistic not so as to insult my fellow hams 
many of whom could run circles around me in RF engineering and radio 
systems but to stay in "generic" terms"....  The fun part to fiber is if 
there is a way someone is figuring a way to "cheat the rules" bending them 
to their own requirements - part of great capability of simple sand fused 
into glass...  Now if only we could build an RF amp by simply contaminating 
a short piece of coax and mixing the proper frequency of intermodulation at 
low power (-6 to -10 dBm) to get 20+dB of amplification like they do with 
EDFA's on fiber....


At 09:16 PM 1/11/00 , Joel B. Black wrote:

 >----- Original Message -----
 >From: Bob Brandel <KG4CGP@arrl.net>
 >To: Jon Ogden <jono@enteract.com>; Ryan K. Brooks <ryan@inc.net>; Joel B.
 >Black <jbblack@mindspring.com>
 >Cc: AMSAT BB <amsat-bb@AMSAT.Org>
 >Sent: Tuesday, January 11, 2000 10:51 AM
 >Subject: Re: [amsat-bb] Fiber Optic Information
 >
 >
 > > We do this stuff in CATV all the time at bandwidths up to 800 MHz, it's
 > > called Fiber Nodes,
 > >
 > > Essentially, Baseband TV signal (Composite audio/Video for a given
 >channel)
 > > to a Modulator to put it at the frequency or channel you really want it
 >on,
 > > then combine the signals to a series of channels, then into a Fiber
 > > Transmitter at the "shack" to convert the Channelized RF to Fiber Optic
 > > Signals, Send over Single Mode Fiber cable (usually a single fiber at 1550
 > > nM) to a Fiber Receiver or Node, the node has the amplification within in
 >
 >In our applications with fiber (OC-12 [12 DS-3's down to individual hub
 >connections we use a multitude of SM and MM - MM in-plant, SM for long-haul.
 >This is not my forte, but it is my understanding that we use laser
 >transmitters for SM and LED transmitters for MM.  Is this true throughout
 >the industry?

Bob Brandel
KG4CGP
Emergency Coordinator, Spotsylvania County, Virginia
ARES Officer
Grid FM18
Roanoke Division, Virginia Section
Member ARRL, AMSAT, ARES, Rappahanock Valley Amateur Radio Club (147.015), 
Woodbridge Wireless


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