On 16/04/14 18:20, Simon Wise wrote:
> 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.
and there are stories around of ridiculously expensive delay units for very
short delays (paid for by US military budgets) and australians replacing them
with a much more reliable, and almost free, solution using some switches and a
circuit board with loops of 1, 2, 4, 8, ... etc centimetres each, but it's the
usual way to do that sort of delay.
Simon
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Received on Wed Apr 16 12:15:04 2014
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