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Author Topic: Velocity Factor  (Read 7346 times)
WB6THE
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Posts: 129




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« on: May 28, 2012, 09:12:55 PM »

Is it that electromagnetic energy travels more slowly...
or.... does it require more time to transit the media
due to the effects of distrubited L/R/C.

Now... IF ...  electromagnetic energy propagates
more slowly how do the photons gain energry to resume
Celearus upon exit? Energy stored in the E and H fields?

What's that got to do with my new 40M dipole?
Nothing, just do as the book says.. but a lot, too.

Maybe its something that I don't really want to know!
I might not be able to understand the truth.

Physics and electronics tell little white lies.

Comments?
WB6THE

 
« Last Edit: May 28, 2012, 09:20:43 PM by WB6THE » Logged
K7MH
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Posts: 347




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« Reply #1 on: May 28, 2012, 10:24:41 PM »

1. Make the antenna put it up and get it tuned (just do what the book says).
2. Get on the air with it and start making some contacts.
3. Read a good book on antennas and such as you have the time.

It's a win win situation that way! Smiley
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N4CR
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Posts: 1702




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« Reply #2 on: May 28, 2012, 11:39:43 PM »

I don't think this is the exact answer to your questions, but I always liked this.

http://www.arrl.org/files/file/Technology/tis/Why%2520an%2520Antenna%2520Radiates.pdf
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73 de N4CR, Phil

Never believe an atom. They make up everything.
K2DC
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« Reply #3 on: May 29, 2012, 04:58:44 AM »

Here's a comment...  In 26 years of Antenna/RF/Microwave Engineering I never heard the word Celearus and I can't find a definition for it.  Care to elaborate?

Don, K2DC

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W5DXP
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« Reply #4 on: May 29, 2012, 05:07:51 AM »

Now... IF ...  electromagnetic energy propagates more slowly how do the photons gain energry to resume Celearus upon exit?

Photons do not change energies due to the velocity factor because that would require them to change frequencies. Photons can travel only at the speed of light in the medium, i.e. they cannot travel at any other velocity than the speed of light. That they appear to you to sometimes be traveling at sub-light speeds is simply the effect of relativity. Use Einstein's technique to visualize what is happening. Position yourself on the crest of a wave and ride along with it. You will not observe any effects from changing VF. You will always be traveling at the speed of light and all the photons will have a constant level of energy.
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WB6THE
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« Reply #5 on: May 29, 2012, 06:18:28 AM »

Celarus is an old scientific term for the speed of light.
It is derived from the Latin word   celer   meaning swift.

WB6THE
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WB6THE
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« Reply #6 on: May 29, 2012, 06:26:54 AM »

Thank you everyone for the replies.
Very interesting.

Alan
WB6THE
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N3OX
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« Reply #7 on: May 29, 2012, 06:55:12 AM »

When a photon passes through a lossless medium with a different speed of light inside the energy stays the same but the momentum changes (momentum is conserved by the photon giving a little "kick" to the medium; it will get an equal and opposite "kick" on the way out)

Energy conservation leaves the frequency (energy = Planck's constant times frequency) the same, but momentum conservation (momentum = Planck's constant divided by wavelength) will cause the wavelength in the medium and the speed of light in the medium to change.
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
NK6Q
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Posts: 202




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« Reply #8 on: May 29, 2012, 07:33:45 AM »

I suppose the "c" in Einstein famous equation stands for "Celearus".

Bill in Pasadena, NK6Q
(moving WAY below Celearus these days)
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WA3SKN
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« Reply #9 on: May 29, 2012, 07:45:51 AM »

Photons???
Electromagnetic waves are based on electrons, so you might want to re-read the book!
And since your formulas are based on the "speed of light" in a vacuum, the "velocity factor" is to correct that to the medium you are working with.
73s.

-Mike.
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N3OX
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« Reply #10 on: May 29, 2012, 10:16:58 AM »

Radio waves are "made of" photons ... Electromagnetic waves in coax and dielectrics and waveguides are an interaction between photons and electrons...

The photon nature of EM waves is pretty irrelevant to radio communications because you can't do any "particle-like" stuff with a trillion quadrillion photons per second moving in coherent lockstep like you get out of the output of a 100W rig at 14MHz.  

But all electromagnetic radiation has a photon description.
« Last Edit: May 29, 2012, 10:21:00 AM by N3OX » Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
N4CR
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Posts: 1702




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« Reply #11 on: May 29, 2012, 10:24:28 AM »

Photons???
Electromagnetic waves are based on electrons, so you might want to re-read the book!

Electrons don't move anywhere near the speed of light. So what does?
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73 de N4CR, Phil

Never believe an atom. They make up everything.
W5FYI
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Posts: 1046




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« Reply #12 on: May 29, 2012, 10:35:25 AM »

Light exists either as photons or electromagnetic waves. In ancient times (late 19th and early 20th Century), scientists wondered how photons could penetrate transparent substances and, at the same time, dislodge electrons from the surfaces of many elements. The real conundrum was; how can light, as photons, pass through a lamp's solid glass envelope, and strike a elemental target to knock electrons free? And, if light is a wave how could it pass from the Sun and stars, through the emptiness of space, to illuminate the Earth? To answer the second question, they invented "ether" as the invisible substance that exists everywhere to convey the "waves" of light. The current belief is that electromagnetic energy can manifest itself as "solid" photons that can travel through the emptiness of space and 'bump" into atoms to release electrons, but those same photons can revert back into electromagnetic energy when they need to travel through transparent materials.

Velocity factor is based on the electromagnetic definition. Just as sound waves can speed up or slow down, or even stop, in various substances, electromagnetic waves can, too. That ""Donald Duck" voice that helium induces is because sound travels nearly three times faster in helium than in air. Water speeds up sound velocity more than 4 1/2 times faster than in air, and solid aluminum can give sound waves a velocity more than 15 times greater than in air!

Electromagnetic waves, likewise, exhibit various velocities in various materials. Water slows the velocity of light to about 75 percent of its velocity in air; glass may slow it to around 60 percent; and diamond to as slow as 41 percent! But, when it exits these materials, it isn't slowed by their density anymore, so it reverts back to its original speed.

Let's say you are a jogger, and your normal jogging speed is 20 m.p.h. You encounter a river or pond along your route, but when you try to run through it, it resists your efforts and you might find yourself going only two or three m.p.h. while exerting the same effort that you used on dry land. However, once you're out of the water hazard, and without increasing your effort, you easily pick up your 20 m.p.h. pace.

In physics, velocity is defined as distance divided by time, so it has nothing to do with energy. A sound or light wave that changes velocity when going into one substance from another, changes back to the original velocity when reentering the original substance.

Likewise, electromagnetic waves are slowed by whatever they have to travel through or along, from the conductor itself to the insulation that might surround it. Consequently, everything the wave has to traverse is analogous to the pond the jogger has to wade through. Once out of the pond (off the wire, out of the insulation), the normal (air, vacuum) velocity will be reestablished without the expenditure of new energy.
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W5DXP
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« Reply #13 on: May 29, 2012, 11:24:04 AM »

Photons??? Electromagnetic waves are based on electrons ...

http://en.wikipedia.org/wiki/Drift_velocity

The velocity of the electrons in the above 3 amp example is 0.00028 meters/second and they change directions every 1/2 cycle of RF, e.g. every 0.05 microsecond at 10 MHz.

The speed of light of EM waves (in free space) is 299,792,458 meters/second, the same as the speed of photons in free space.

There are not enough free electrons in free space to support electromagnetic waves, i.e. free space is an insulator, not a conductor.

... the momentum changes (momentum is conserved by the photon giving a little "kick" to the medium; it will get an equal and opposite "kick" on the way out)

I wonder if Einstein, while riding the crest of the EM wave, could detect a change in momentum?
« Last Edit: May 29, 2012, 11:27:45 AM by W5DXP » Logged
STAYVERTICAL
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Posts: 875




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« Reply #14 on: May 29, 2012, 12:41:34 PM »

I have to tip my hat to you guys who know far more than I could ever imagine.
Not being a physicist or engineer, I too, as a layman, thought that photons were bits of light, so my education has been extended.

I have probably been watching too many PBS programs, but I wonder if in a century (or less) scientists will have a different view of
reality than we currently hold.
From my limited understanding of Quantum effects and other such esoteric concepts which seem to be rock solid in both theory and experimentation,
it seems to me, that something is not quite right in our view of the universe.

Perhaps we are all in Plato's cave allegory, where we are forming our view of the universe based on shadows thrown on a cave wall.
Quantum entanglement, spooky action at distance, shroedingers cat - I can't shake the feeling that there is truth in the statement made by hamlet:
"There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy".

There is nothing scientific in my observation, and I am in agreement that science and technology work perfectly well with our current theories.
But like the prevailing attitude when Newton published his tome "Principia Mathematica", that the laws of the universe were finally explained,
time has a way of humbling our hubris.
Although Newtons laws are still valid on the macro level, the old idea of mechanism by Laplace, has long been displaced by the
probabilistic universe of Bohr and Heisenberg.

It will be interesting to see what ideas in the future will do to advance our view of reality, but of one thing I am certain -
we will probably think we are close to the understanding the whole universe.
Then, like Tantalus grasping for the fruit just out of his reach, we will wonder why we cannot find that last little piece of the puzzle.

But then, this is what makes humans advance - our endless curiosity to find out what makes things tick.

73 - Rob

 
« Last Edit: May 29, 2012, 12:54:19 PM by STAYVERTICAL » Logged
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