wjm@lcuxc.UUCP (B. Mitchell) (01/22/85)
<munch,munch,munch>
Yes, the bandwidth of a telephone channel is limited to 2700 Hz (300 Hz to
3 KHz), therefore 4800 and 9600 baud modems must use more than a straight
binary coding scheme in order to fit this bit rate into the channel.
What they do is use multiple level schemes and forms of phase modulation to
place more than one bit of information into one hertz of bandwidth.
The amount of information that can be transferred through any communications
channel is given by Shannon's theorem and is a function of the channel bandwidth
and its signal-to-noise ratio. Of course, one should remember that Shannon's
theorem is the theoretical limit, and that most practical systems do not do
as well. However, it is impossible to do better than the theoretical value.
186,000 miles per second .... Its not just a good idea - its the LAW !!
Bill Mitchell ({ihnp4!}lcuxc!wjm)