On 17/04/14 12:11, Gene Heskett wrote:
On Wednesday 16 April 2014 21:57:21 Simon Wise did opine:
On 16/04/14 23:20, Gene Heskett wrote:
On Wednesday 16 April 2014 09:09:06 Simon Wise did opine:
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.
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. :)
not at all convinced that a fast oscilloscope, a good calculator and the
wet-ware connecting them are simpler than a bit of machined metal with
gold plating, but certainly re-using existing gadgets beats making new
ones.
Either method requires that the operator have intimate knowledge of the
characteristics of the transmission line being measured. That is
considerably more important then the cost of the tool, particularly when
the results are adequate for the job at hand.
indeed, it is often so
Simon
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