[sdiy] Re: Speed of electrons? (was mass extinction of the dinosaurs)

[John L Marshall]

Stripline and other transmission line techniques are frequently used to
build computer buses and backplanes so that the signals stay clean and to
minimize standing waves. I will assume a worst case velocity factor of about
0.66 or about 8.6 inches per nanosecond.

Wire antennas are assumed to have a velocity factor close to one minus 5%
for end effect (capacitance).

Open wire transmission lines have a velocity factor of about 0.97.
Television twin lead has a velocity factor of about 0.82.
That lossy stuff, RG-174 has a velocity factor of about 0.66.

Years ago, Dawn VME products had a technical article describing how computer
buses should designed and modeled as transmission lines.

PC computer front side buses are now running at 400 MHz. That is blazing
saddles, man.

----- Original Message -----
From: KA4HJH <ka4hjh at gte.net>
To: John L Marshall <john.l.marshall at gte.net>
Cc: <synth-diy at dropmix.xs4all.nl>
Sent: Monday, July 23, 2001 2:52 PM
Subject: Speed of electrons? (was mass extinction of the dinosaurs)


> >The Digital Heads think in only terms of 0 and 1. The transition from 0
to 1
> >IS analog. That is where significant engineering skill is required.
> >
> >I point out in class that a nanosecond is about a light-foot.
>
> That's for massless particles in a vacuum (~.98'/s). Electrons in copper
> wire are much slower. Years ago in Byte there was an article about DRAM
> where they through out a figure like .25" per nanosecond at 5V in copper
> traces (they used the reciprocal of 4 seconds per inch--I think). But I've
> wondered about this ever since. Does anyone have accurate figures on this?
>
> --
>
> Terry Bowman, KA4HJH
> "The Mac Doctor"
>