Re: [LAU] hardware - Intel CPUs

On Wednesday 16 April 2014 09:09:06 Simon Wise did opine:

> On 16/04/14 17:19, david wrote:
> > Interesting. What is the difference between speed of sound in air and
> > the speed of electricity through a cable?
>
> sound is about 3ms per metre (330 m/s) in air
>
> ... in a room, talking about sound, there is no significant delay for
> the signal in the cable ... from Sydney to Hawaii via copper or fibre
> yes, considering phase differences for RGB video signals in a building
> yes, talking about timing on a circuit board or a bus while syncing
> gigahertz clocks yes, but for sound within a building the speed over
> copper may as well be infinite.
>
>
> I was shown a rather nice artwork that used high resolution radar
> (resolutions around 1 centimetre I think) to get positions (it was made
> in a university robotics department that had such things!). The way
> those work is very interesting ... the frequencies are way to high to
> digitise, so the electronics has to be all analogue ... the 'circuitry'
> is basically plumbing ... gold lined tubes and chambers using
> resonances and such to measure delays and phase differences. At those
> frequencies the speed of light becomes a dominant consideration.
>
>
> Simon

We have a gismo thats basically much simpler than all that plumbing, to use
when checking a cable for damage, called a Time Domain Reflectometer. The
pro versions using a tunnel diode switch as a pulse generator, can tell you
theres a bullethole in the line 883.6' out from where you are hooked up.
I've made homemade versions using a pulse generator and a fast oscilloscope
to measure the echo delay, punched some buttons on a good calculator and
then told the tower crew where to open it up and replace a burned up
connector bullet and/or the teflon disk holding it centered in the line.
It got the job done so I figured it was good enough for the girls I go
with. :)

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Cheers, Gene

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