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[Towertalk] SWR & Speed of Light?

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Subject: [Towertalk] SWR & Speed of Light?
From: (Jon Ogden)
Date: Wed, 25 Sep 2002 22:47:42 -0500
Oh gosh, it goes back a bit to wave theory, but there's a couple of
different "velocities" when speaking about interfering waveforms.  The
"group velocity" CAN indeed be faster than the speed of light if I remember
correctly (All my EM books are in my office so I can't look this up.).
However, the propagation velocity is always the speed of light in that

Remember as well, that the speed of light varies depending upon the
dielectric constant of the medium through which it is propagated.  So I can
send a signal via a coax with one Dk and the same signal through a coax with
a different Dk and the two signals would arrive at the destination at
different times.

The bottom line is that as of now, no one has still been able to prove
Einstein's Theory of Relatively incorrect.  Being able to travel faster than
the speed of light would do that.



on 9/25/02 7:41 PM, Larry L Lindblom at wrote:

> This is clipped from New Scientist.  Though not mentioned directly in the
> article my wild  guess is this effect is somehow due to SWR or something
> akin to it.  What do the feed line experts on the reflector have to say?
> Speed of light broken with basic lab kit
> Scientists have sent light signals at faster-than-light speeds over the
> distances of a few meters for the last two decades - but only with the
> aid of complicated, expensive equipment. Now physicists at Middle
> Tennessee State University have broken that speed limit over distances of
> nearly 120 meters, using off-the-shelf equipment costing just $500.
> Jeremy Munday and Bill Robertson made a 120-metre-long cable by
> alternating six- to eight-metre-long lengths of two different kinds of
> coaxial cable, each with a different electrical impedance. They hooked
> this hybrid cable up to two signal generators, one of which broadcast a
> fast wave, the other a slow one. The waves interfere with each other to
> produce electric pulses, which can be watched using an oscilloscope.
> Any pulse, whether electrical, light or sound, can be imagined as a group
> of tiny intermingled waves. The energy of this "group pulse" rises and
> falls over space, with a peak in the middle. The different electrical
> resistances in the hybrid cable cause the waves in the pulse's rear to
> reflect off each other, accelerating the pulse's peak forward.

Jon Ogden
NA9D (ex: KE9NA)

Life Member: ARRL, NRA
Member:  AMSAT, DXCC

"A life lived in fear is a life half lived."

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