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)
Keywords: Shannon, 9600, V.32, V.42, bis
Message-ID: <1990Dec12.153041.20357@sparrms.ists.ca>
Date: 12 Dec 90 15:30:41 GMT
References: <136548@pyramid.pyramid.com> <16309@cbmvax.commodore.com> <1990Dec10.162413.13959@sparrms.ists.ca> <1990Dec11.185205.13752@wsrcc.com>
Organization: Spar Aerospace Ltd, Toronto, Canada
Lines: 20

In <1990Dec11.185205.13752@wsrcc.com> wolfgang@wsrcc.com (Wolfgang S. Rupprecht) writes:

>>And so on to a discussion based on dubious assumptions...
>>My book on information theory gives Shannon's result as:
>>    Channel Capacity = Bandwidth * log2( 1 + SignalPower/NoisePower )
>>Bandwidth for telephony ~= 3.4KHz
>>Telebit, in their literature for the T2500 Modem, claim "up to" 18000bps
>>in PEP mode without compression. To achieve this, the S/N power ratio would 
>>have to be >15.8dB.

>I wouldn't be surprised to hear that the 18k tb+ spec assumed that you
>connected the two modems with a 3ft section of phone patch cord.

Telebit Trailblazer Plus brochure states:

"Dial-up asynchronous connections at speeds of up to 19,200 bps with
 data compression, 18,000 bps without data compression". 

(I think the 19,200 limit is due to the Trailblazer supporting a maximum
DTE speed of 19,200).