16 Apr
2014
16 Apr
'14
1:20 p.m.
On Wednesday 16 April 2014 09:09:06 Simon Wise did opine:
On 16/04/14 17:19, david wrote:
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. :)
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 _______________________________________________
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Cheers, Gene
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