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From: js2j@mhuxt.UUCP (sonntag)
Newsgroups: net.physics
Subject: Re: purplexing multiplexing question....
Message-ID: <624@mhuxt.UUCP>
Date: Tue, 26-Feb-85 16:40:36 EST
Article-I.D.: mhuxt.624
Posted: Tue Feb 26 16:40:36 1985
Date-Received: Thu, 28-Feb-85 12:48:31 EST
References: <2117@drutx.UUCP>
Organization: AT&T Bell Laboratories, Murray Hill
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> can anyone explain the difference between "time-division" and
> "frequency-division" multiplexing in laymans' terms?
> either mail or net posting is OK...
> mail: ihnp4!drutx!grm

     Its really a pretty simple concept.  Suppose you want to send several
signals through one channel.  One way is to use time-division multiplexing,
in which signal A uses the channel for a certain amount of time, signal B
uses it next, etc.  An example of this is television, where a given channel
passes signals from commercial A, then commercial B, ... , commercial G,..,
then some mindless program gets ten minutes, and it more or less repeats.
    Another way to share a single channel is frequency division multiplexing.
In this scheme, each signal is mixed from the baseband to a seperate
carrier frequency, and they are all added together to go through the
channel.  At the other end of the channel, bandpass filters centered at
the correct carrier frequencies seperate the signals, and they are mixed
back down to the baseband.  Television is an example of this as well, though
in a different way.  Think of 'channel' above as the path through the air
from the transmitter to your antenna.  Changing the channel on your television
changes the center frequency of the bandpass on the input and the frequency
which is used to mix the bandpass output back down to the baseband.
-- 
Jeff Sonntag
ihnp4!mhuxt!js2j
    "Would you like to swing on a star?
     Carry moonbeams home in a jar?
     And be better off than you are?
     Or would you rather be a fish?"