Routing radio signals around objects
 

jawod wrote:

You know, I've always been puzzled by negative refraction. The basis of
positive refraction is that the speed of EMR (say light) decreases
within a given material. In negative refraction, the speed of light
INCREASES?

I guess as long as it is less than the speed of light in a vacuum, no
laws have been broken?

I know very little about optics, but the velocity factor of EM waves in
hollow waveguide is always greater than one, that is, the phase velocity
is always greater than the speed of light. In fact, it increases as the
frequency lowers, approaching infinity at the cutoff frequency.

What prevents it from breaking any laws is that the group velocity,
which is the speed at which any change or information can be sent, is
always less than the speed of light.

I suspect that negative refraction is related to this, but will leave it
to the optics experts to say for sure.

Roy Lewallen, W7EL

Routing radio signals around objects
 

Roy,
I haven't reviewed the physics of relativity lately, but I 'believe'
that value of C is specified as the velocity of energy propagation in a
vacuum... SInce that limit is not violated when the wave front is
propagating in a medium with a refractive index greater than vacuum,
i.e. C is slower than in a vacuum, then by O'Connor's Law of
Reciprocity the limit will not be broken if the the wave front is
propagating a medium with a refractive index less than a vacuum, i.e. C
is greater than in a vacuum...

denny / k8do

Routing radio signals around objects
 

Denny wrote:
Roy,
I haven't reviewed the physics of relativity lately, but I 'believe'
that value of C is specified as the velocity of energy propagation in a
vacuum... SInce that limit is not violated when the wave front is
propagating in a medium with a refractive index greater than vacuum,
i.e. C is slower than in a vacuum, then by O'Connor's Law of
Reciprocity the limit will not be broken if the the wave front is
propagating a medium with a refractive index less than a vacuum, i.e. C
is greater than in a vacuum...

denny / k8do

Denny

I'm afraid I don't understand your post at all. Perhaps you are kidding
and I am fished in. So be it.

I do not understand how EMR can travel in any medium "faster" than in a
vacuum. Regarding Ray's post, I don't have a precise definition of
velocity factor but I suspect it is not describing wave propagation
directly. (And I am speaking as a total mathematical pedestrian :)

Negative refraction is damned puzzling ... and fascinating. Richard
seems to have the best links on the subject.

John
AB8O

Routing radio signals around objects
 

jawod wrote:
. . .
I do not understand how EMR can travel in any medium "faster" than in a
vacuum. Regarding Ray's post, I don't have a precise definition of
velocity factor but I suspect it is not describing wave propagation
directly. (And I am speaking as a total mathematical pedestrian :)
. . .

Suppose you put a 1 GHz signal into a waveguide and stopped time so you
could look at it. Measure the distance taken up by one complete cycle,
and you'll find that it's greater than c/f. (In a vacuum, the distance
is c/f, and in a medium with velocity factor less than 1 it's less.) Now
start time up again, and look at just one spot along the waveguide. Sure
enough, a whole cycle goes by every ns. Sure looks like it's going
faster than c. This is the phase velocity.

But if you turn the signal off at one end of the waveguide and measure
how long it takes for it to disappear at the other, dang. The change
travels at the group velocity, which is never faster than the speed of
light.

Roy Lewallen, W7EL

Routing radio signals around objects
 

John, it's all relative...

You need to do some basic reading...
First for antenna knowledge:
Walter Maxwell's book, Reflections II - most highly recommended by me -
and will clear up why you can't just 'fold' half of the dipole EM
around the arc of a circle to get more gain...

The ARRL antenna Handbook - pay particular attention to the Smith Chart
instructional..
John Krause, W8JK's, college text on antennas called, 'Antennas'

For basic physics of EM waves
'Dummy' series on physics
Start with Richard Feynman's public lecture series of popular books,
especially his QED...
Any college level text on physics and optics..

For that special moment with a loved one:
Any popular level book on the Special Theory of Relativity...

Unfortunately for non speakers, like the language of Spanish is
spanish, the language of all science is mathematics... Get the 'Dummy"
series book on algebra and do enough of the problems so that basic
equations don't panic you... This alone will make most of the
university level science books accessible...

I'll leave the Calculus to your discretion

I use the 'Dummy' series of books for skimming any topic that I lack
the basics in... Well done for the most part - or maybe I just don't
'get' the ones I thought weren't well done, eh?..

cheers ... denny / k8do


Roy Lewallen wrote:
jawod wrote:
. . .
I do not understand how EMR can travel in any medium "faster" than in a
vacuum.

Routing radio signals around objects
 

Denny wrote:
John Krause, W8JK's, college text on antennas called, 'Antennas'

A "Best Buy" at $15.49 (1/3 the price of the ARRL Antenna Book)

http://www.abebooks.com/servlet/Sear...072321032&x=73

--
73, Cecil http://www.w5dxp.com

Routing radio signals around objects
 

Ipaid almost $100 fot the 1955 edition of "Antennas" by John Kraus.

Something sounds fishy here.

/s/DD

Cecil Moore wrote:

Denny wrote:

John Krause, W8JK's, college text on antennas called, 'Antennas'


A "Best Buy" at $15.49 (1/3 the price of the ARRL Antenna Book)

http://www.abebooks.com/servlet/Sear...072321032&x=73

Routing radio signals around objects
 

Dave wrote:
Ipaid almost $100 fot the 1955 edition of "Antennas" by John Kraus.
Something sounds fishy here.

It's the international paperback edition in black and
white on non-glossy paper but contains all the information
in the domestic version. (The "fishy" part is that it's
a gray market book and not supposed to be available to US
citizens.)

Cecil Moore wrote:

Denny wrote:
John Krause, W8JK's, college text on antennas called, 'Antennas'

A "Best Buy" at $15.49 (1/3 the price of the ARRL Antenna Book)
http://www.abebooks.com/servlet/Sear...072321032&x=73
--
73, Cecil http://www.w5dxp.com