Xref: utzoo comp.sys.ibm.pc:26166 comp.dcom.lans:2555 comp.dcom.modems:3585
Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!amdahl!pacbell!stream!jim
From: jim@stream.UUCP (Mr. Jim's Own Logon)
Newsgroups: comp.sys.ibm.pc,comp.dcom.lans,comp.dcom.modems
Subject: Re: RS-232 vs. V.35
Summary: Distance and baud rate are interdependant
Keywords: maximum distance
Message-ID: <351@stream.UUCP>
Date: 15 Mar 89 23:15:14 GMT
References: <1766@umbc3.UMBC.EDU> <4287@ingr.com> <7369@boulder.Colorado.EDU>
Distribution: na
Organization: Bell Technologies, Fremont, CA
Lines: 24

In article <7369@boulder.Colorado.EDU>, bobk@boulder.Colorado.EDU (Bob Kinne) writes:
> The max distance and the baud rate are interdependent.  In McNamara's book
> "Technical Aspects of Data Communications" on page 240 there is an analysis
> with graphs.   Briefly, at 1200, 3000ft shielded or un, at 4800, 1000ft
> shielded, 250ft unshielded, at 9000, 250ft either way.

   While I hold the McNamara bible in high esteem, some of the graphs are
misleading and incorrect. This is such a case.  For almost any transmission
medium, there is a speed distance product. The simplest way to prove this
is the Capacitive Reactance of the cable:  X(c) = 1/(2 (Pi) F C ) 

   This is the AC resistance to ground. As the capacitance goes up (longer
cable length) the resistance to ground goes down (less signal). The frequency
(F) plays the same role, as F increases, the resistance to ground decreases.

   Depending on the cable that you have, X(c) may or may not be a dominant
factor at the speed and distance you are considering. RS232, V35, fiber
optics, the same principals apply. 

   McNamara is just showing what 90% of the people are satisfied with 90%
of the time. Just hope that you have 90% of their environment....

							-Jim Wall
							 Bell Technologies