Path: utzoo!utgpu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!ists!sparrms!sparatd!mb
From: mb@sparrms.ists.ca (Mike Bell)
Newsgroups: comp.dcom.modems
Subject: Re: Capacity of a Channel (Was: Inexpensive 9600 baud modems)
Message-ID: <1990Dec12.154139.20496@sparrms.ists.ca>
Date: 12 Dec 90 15:41:39 GMT
References: <1990Dec10.162413.13959@sparrms.ists.ca> <4986@optilink.UUCP>
Organization: Spar Aerospace Ltd, Toronto, Canada
Lines: 19

In <4986@optilink.UUCP> witkowsk@optilink.UUCP (Dave Witkowski) writes:

>> My book on information theory gives Shannon's result as:
>> 
>>     Channel Capacity = Bandwidth * log2( 1 + SignalPower/NoisePower )
>> 
>> Anybody know what Signal/Noise ratios are likely to be found on
>> normal phone lines? This would give an indication of the practical
>> limit to modem speeds.
>>

>Idle channel noise per BellCore TRY-0064 is:

>20dBrnC for C-message weighting
>39dBrn for 3-KHz flat response

For those without calculators to hand, these suggest:
	20db with 3k4Hz bandwidth -> 22640 bps (not sure what C-message means!)
	39db with 3khz  bandwidth -> 38870 bps