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Re: Doppler and Light Speed



Forget the point about gravity below. Gravity is too complex. By the way,
the speed of gravity could be a lot faster than the speed of light.


----- Original Message -----
From: "Pieter Ibelings" <elpieter@hotmail.com>
To: "James Alderman, KF5WT" <kf5wt@verizon.net>; <amsat-bb@AMSAT.Org>
Sent: Sunday, December 16, 2001 2:17 PM
Subject: Re: [amsat-bb] Doppler and Light Speed


> Hi James,
>
> About Doppler:
> I do not think doppler is created anywhere. A moving receiver toward a
> signal source cannot tell the difference between what it sees and a higher
> frequency source if it was stationary. The receiver just sees a higher
> frequency because it encounters the wavefront at a shorter period. Let's
> leave that one there :)
>
> Now on the propagation of radio waves. You commonly hear in school text
> books that radio waves start at 20 or so KHz and everything below is sound
> waves. In reality, radio waves could be any frequency even 20 KHz. So you
> can have a 20 KHz sound wave that you can hear and also have a 20 KHz
radio
> wave traveling through the air. What makes the differencee between sound
and
> radio waves is how they are propagating.  Sound travels in a longuitudinal
> wave by compressing and rarefying air. The wave travels in the direction
of
> propagation. Radio waves , on the other hand, will propagate in transverse
> waves because the wave moves at right angles to the direction of
> propagation. In other words, the radio waves look like water waves because
> the motion of the water is up and down, or at right angles to direction of
> propagation. An interesting point to make is that sound waves travel
faster
> in denser mediums and slower in low density ones. Sound waves in the gound
> will travel a lot faster than in air and will not travel in a vacuum.
Radio
> waves are the contrary. They will travel at the speed of light
(abbreviated
> "c" which is the speed of light in a vacuum). In order to make a radio
wave
> speed up, you would have to lower the density of the medium by removing
all
> of the molucules and interactions that might slow the light down. A vacuum
> already has nothing in it so that is as fast as you can go. If someone
ever
> figures out how to make light go faster than the speed of light in a
vacuum,
> please let me know. Another very inportant point is that for something to
> travel at the speed of light, it cannot have any mass.
>
> Back to basic radio propagation. When radio waves propagate through a
> medium, they interact electrically and magnetically with the medium. There
> is a measure on how much the medium interacts electrically and
magnetically.
> These are the permittivity and permeability of the medium. Some materials
> have more of one than the other. The important thing is that the speed of
> light will be around 299,792.458 km/s in a vacuum and it can be derived
from
> a simple formula c=square root of (mu0/e0) where mu0 = the permeability of
> free space and e0 if the permittivity of free space. This means that you
can
> measure the permeability and permittivity of lets say glass and you can
> easily calculate how fast light will travel through it. Free space is
> another word for a very good vacuum. Since yiou cannot remove anything
from
> free space, there is your maximum speed. You can get lower, but not
faster.
> Some people will argue that things can travel faster, but I am not holding
> my breath.
>
> You can speed the RF in a coax by removing things that are slowing it
down.
> You not necessarily need more energy. A boat with a 100 HP engine will
move
> faster in water than in tar. A rf signal will travel faster in an air
> dielectric coax than in a teflon dielectric coax. To make it go faster
than
> in an air dielectric coax will involve removing the air. Even after you do
> all these things, you wont get any faster than the speed of light in a
> vacuum.
>
> Some bonus interesting points:
>
> 1. The speed of light seems to be changing with time :). The permeability
> and permittivity of free space appear not to be constant with time
>
> 2. When you travel faster than the speed of sound, you get a sonic boom. A
> bullet can travel faster than the speed of sound.
>
> 3. Travelling faster than the speed of light in a transverse mode is
pretty
> much ruled out. Pretty much nothing can travel any faster in this mode.
> Unless something really weird is out there :)
>
> 4. Gravity travels at the speed of light and does not seem to be affected
by
> permeability and permittivity. If it travels at squareroot of (mu0/e0),
why
> is it not affected by them? By the way, gravity could possibly travel a
> little faster than light.
>
> 5. When you travel faster than the speed of light, you get a light boom.
You
> can make these in the lab :)
>
>
>
> ----- Original Message -----
> From: "James Alderman, KF5WT" <kf5wt@verizon.net>
> To: <amsat-bb@AMSAT.Org>
> Sent: Sunday, December 16, 2001 12:57 PM
> Subject: [amsat-bb] Doppler and Light Speed
>
>
> > Greetings Fellow Satellite Enthusiasts,
> >
> > Thanks to all of you who responded to my question about Doppler shift.
I
> > must say I learned a lot more than I expected.  We truly have a vast
> > reservoir of knowledge out there in the amateur satellite community.
> >
> > The general answer to my inquiry seems to be this:  Doppler is not
really
> a
> > condition that "exists", like voltage drop across a resistor, or AC
phase
> > shift across a capacitor.  Those conditions would be present whether I
> were
> > there measuring them or not.
> >
> > Doppler is more of a phenomena that is "observed."  Doppler is an
observed
> > phenomena similar to the strobing effect we observe in some movies where
a
> > car's wheels may appear to be turning backwards.  Of course, the wheels
> > aren't really turning backwards.  They just appear to be because of the
> > frame rate of the motion picture film.  (We might see this same type of
> > observed phenomena when a fan appears to be turning backwards, or very
> slow,
> > under a fluorescent light.)
> >
> > In a like manner, Doppler shift from a satellite may be observed by one
> guy
> > on the ground, while at the same time a guy flying along in space with
the
> > satellite would observe no Doppler at all.
> >
> > As for my question as to where Doppler occurs, I'm convinced that it
> > "happens" at the point where it is observed.  If I'm standing along side
a
> > train track, the Doppler "occurs" when those compressed sound waves
strike
> > my ear.
> >
> > If I'm monitoring a satellite beacon, Doppler for me "occurs" when the
RF
> > strikes my antenna and is converted to voltage which my receiver picks
up.
> > In other words, if we must say that Doppler occurs somewhere, it happens
> > wherever you receive the signal.
> >
> > Now I have a question about the speed of radio waves.  We read in the
> books
> > that radio waves travel at the speed of light in free space.  We also
read
> > that in the atmosphere, they travel a bit slower than light speed.  If
> > atmosphere can slow a signal down, can lack of atmosphere speed it up?
> >
> > If a satellite is beaming a signal to me, the RF travels at light speed
> > until it enters the atmosphere, then it slows down.  If I beam a signal
to
> > the satellite, my RF travels slower than light speed through the
> atmosphere.
> > What happens when the signal breaks into free space?  Does it speed back
> up
> > to light speed?  If so, where does it get the energy needed to increase
> its
> > speed?
> >
> > I'm convinced that RF must have the ability to increase in speed.  RF
> > travels at about 60% of light speed in a transmission line (assuming the
> > velocity factor or the coax is .6), and at nearly full speed when it
> reaches
> > the antenna and is sprayed out into the air.
> >
> > Here's the question:  Am I right that RF does increase in speed?  If so,
> > where does the energy come from which accelerates the waves?
> >
> > Since I'm not subscribed directly to the reflector, please also reply
> > directly to me so I can conveniently see your response.  Thanks for your
> > technical advise.
> >
> > 73, James Alderman, KF5WT
> > Dallas, TX
> >
> >
> >
> >
> > ----
> > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> >
>
----
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