Xref: utzoo comp.sys.ibm.pc:26173 comp.dcom.lans:2556 comp.dcom.modems:3586 Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!bionet!ames!lll-winken!lll-lcc!pyramid!csg From: csg@pyramid.pyramid.com (Carl S. Gutekunst) Newsgroups: comp.sys.ibm.pc,comp.dcom.lans,comp.dcom.modems Subject: Re: RS-232 vs. V.35 Keywords: maximum distance Message-ID: <62766@pyramid.pyramid.com> Date: 16 Mar 89 08:33:37 GMT References: <7369@boulder.Colorado.EDU> <351@stream.UUCP> Distribution: na Organization: Pyramid Technology Corp., Mountain View, CA Lines: 20 In article <7369@boulder.Colorado.EDU>, bobk@boulder.Colorado.EDU (Bob Kinne) writes: >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 ) As long as we're splitting hairs.... The aspect that throws this off is we're talking about square waves, not sine; reactance is higher for the higher har- monics, thus "rounding" the theoretically square digital signal. Which is why both RS-232-C and V.35 specify "cable length" only in terms of C, with an assumed constant F (20kHz and 48kHz, respectively), plus a mess of require- ments regarding limited slew rates and zero crossing times. (Don't tell me about F being half the 20000bps or 48000bps bit rate. The data signals are 10kHz and 24kHz, but the clock signals are 20kHz and 48kHz. And anybody who doesn't think those clocks have to be squeaky clean has never tried building a large SNA or X.25 network. :-)) Whew! Have we sufficiently beaten this subject to death now? :-)