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From: blymn@awadi.com.au (Brett Lymn)
Newsgroups: comp.os.linux.development,comp.os.linux.misc,comp.os.386bsd.questions,comp.os.386bsd.misc,sci.electronics
Subject: Re: 16550 detection
Date: 15 Nov 1994 10:07:19 GMT
Organization: AWA Defence Industries
Lines: 38
Message-ID: <BLYMN.94Nov15203720@mallee.awadi.com.au>
References: <jonkCyo2Au.239@netcom.com> <Cyp2ws.MIq@bonkers.taronga.com>
<jonkCypCzF.Jrq@netcom.com> <CywsH9.K05@zoo.toronto.edu>
NNTP-Posting-Host: mallee.awadi.com.au
In-reply-to: henry@zoo.toronto.edu's message of Mon, 7 Nov 1994 17:55:56 GMT
>>>>> "Henry" == Henry Spencer <henry@zoo.toronto.edu> writes:
In article <CywsH9.K05@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes:
Henry> In article <jonkCypCzF.Jrq@netcom.com> jonk@netcom.com
Henry> (Jonathan Dale Kirwan) writes:
>> : Finally, external modems make great external fuses for minor
>> power surges : over the phone line. I'd rather not have that
>> plugged into my bus.
>>
>> In the US, at least, phone lines theoretically have to have
>> adequate arresters before the line enters the house or
>> building...
Henry> Arresters -- to the extent that they protect your side of
Henry> things at all, as opposed to protecting the phone company's
Henry> hardware -- are directed at preventing fires, not damage to
Henry> electronics. That's a whole different order of magnitude,
Henry> offering no useful protection for your modems.
WARNING WARNING: Eye glaze material ahead!
Actually a lot of telecom companies do not like putting suppression
devices on their lines because it *can* make things worse. During
something like a lightning strike your wires sorta cease acting in a
nice predictable manner and start being more like waveguides. If you
put and impedance transition in the wrong place then you can get the
lightning impulse bouncing with a phase reversal which *doubles* the
voltage seen (the impulse is sorta the same as putting a pulse down a
bit of string, the effect at the other end depends on whether the
string end is fixed or free to move). It sounds crazy, it is crazy
but when you are talking lightning with huge volts/amps trusty ole
'tricery all the "normal" rules go out the window.
Brett"An electrical eng in a very strange job"Lymn
--
Brett Lymn