| Topic: |
Science > Physics |
| User: |
"krishna" |
| Date: |
08 Nov 2005 03:56:06 AM |
| Object: |
electromagnetism |
Hi list,
Iam quite new to this list and happened to discover this while
browsing for vxworks(rtos)groups.I always had a strong liking towards
physics and reasoning.Coming to my question,it is about transmission of
data in wireless fashion.
Any signal is modulated and then transmitted while at the recieving end
it is demodulated and used.Iam unable to understand the concept of
modulation from the quantum physics point of view.Firstly what happens
to the energy/wave when it gets modulated?
All the time I get the response theoretically in terms of change in
waves' shape.
But how is it going to help?Can't a simple trans./recv. ckt not
suffice?
Can some one please explain.
thank you.
cheers-
kaushal.
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| User: "Greg Neill" |
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| Title: Re: electromagnetism |
08 Nov 2005 06:33:31 AM |
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"krishna" <kaushal.r@gmail.com> wrote in message
news:1131443766.289059.213000@o13g2000cwo.googlegroups.com...
Hi list,
Iam quite new to this list and happened to discover this while
browsing for vxworks(rtos)groups.I always had a strong liking towards
physics and reasoning.Coming to my question,it is about transmission of
data in wireless fashion.
Any signal is modulated and then transmitted while at the recieving end
it is demodulated and used.Iam unable to understand the concept of
modulation from the quantum physics point of view.Firstly what happens
to the energy/wave when it gets modulated?
All the time I get the response theoretically in terms of change in
waves' shape.
But how is it going to help?Can't a simple trans./recv. ckt not
suffice?
Can some one please explain.
thank you.
Amplitude, frequency, or phase modulation?
.
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| User: "FrediFizzx" |
|
| Title: Re: electromagnetism |
09 Nov 2005 01:29:03 AM |
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"krishna" <kaushal.r@gmail.com> wrote in message
news:1131443766.289059.213000@o13g2000cwo.googlegroups.com...
| Hi list,
| Iam quite new to this list and happened to discover this
while
| browsing for vxworks(rtos)groups.I always had a strong liking towards
| physics and reasoning.Coming to my question,it is about transmission
of
| data in wireless fashion.
|
| Any signal is modulated and then transmitted while at the recieving
end
| it is demodulated and used.Iam unable to understand the concept of
| modulation from the quantum physics point of view.Firstly what happens
| to the energy/wave when it gets modulated?
| All the time I get the response theoretically in terms of change in
| waves' shape.
| But how is it going to help?Can't a simple trans./recv. ckt not
| suffice?
| Can some one please explain.
| thank you.
Amplitude modulation should be just more or less photons of about the
same frequency. If you know what the value of the electric wave
amplitude is at the peak of the modulation and what it is at the trough
of modulation, you can get an estimate of the average number of photons
that is varying. For free space the following expression should give
you a good estimate.
|E_0|^2 = hbar*w^4*n/(4pi^2*c^3)
Where n is the number of photons with angular frequency, w = omega on
average. So solve that for n and plug in the electric field value and
angular frequency in gaussian cgs units. So if you have an electric
field of 1 volt/meter and an angular frequency of 1 megahertz, this
gives an average photon number of about 1.1x10^27. Lots of photons!
Don't try to count them. ;-)
FrediFizzx
http://www.vacuum-physics.com/QVC/quantum_vacuum_charge.pdf
or postscript
http://www.vacuum-physics.com/QVC/quantum_vacuum_charge.ps
http://www.vacuum-physics.com
.
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| User: "Old Man" |
|
| Title: Re: electromagnetism |
08 Nov 2005 06:21:35 PM |
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"krishna" <kaushal.r@gmail.com> wrote in message
news:1131443766.289059.213000@o13g2000cwo.googlegroups.com...
Any signal is modulated and then transmitted while at the recieving end
it is demodulated and used.Iam unable to understand the concept of
modulation from the quantum physics point of view.Firstly what happens
to the energy/wave when it gets modulated?
The energy density, u, of an electromagnetic field with
instantaneous electric field strength, E, and magnetic field
strength, B, is
u = ( 1 / 8*pi ) [ E^2 + B^2 ]
for a modulated plane wave,
E(x, t) = B(x, t) = E0(t) * exp[ i ( k*x - w*t ) ]
The photon number density is n = u / hbar*w. Thus,
the photon number density for a modulated plane wave is
n( x, t ) = ( 1 / 4*pi*hbar*w ) {E0(t)*exp[ i ( k*x - w*t )]}^2
kaushal.
[Old Man]
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| User: "" |
|
| Title: Re: electromagnetism |
09 Nov 2005 02:29:51 AM |
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Dear Cheers Krishna
I too have this doubt while going through qunatum physics. Can someone
help out us in this case.
Chaitanya.
krishna wrote:
Hi list,
Iam quite new to this list and happened to discover this while
browsing for vxworks(rtos)groups.I always had a strong liking towards
physics and reasoning.Coming to my question,it is about transmission of
data in wireless fashion.
Any signal is modulated and then transmitted while at the recieving end
it is demodulated and used.Iam unable to understand the concept of
modulation from the quantum physics point of view.Firstly what happens
to the energy/wave when it gets modulated?
All the time I get the response theoretically in terms of change in
waves' shape.
But how is it going to help?Can't a simple trans./recv. ckt not
suffice?
Can some one please explain.
thank you.
cheers-
kaushal.
.
|
|
|
|
| User: "Dr Photon" |
|
| Title: Re: electromagnetism |
08 Nov 2005 07:06:20 AM |
|
|
krishna wrote:
Any signal is modulated and then transmitted while at the recieving end
it is demodulated and used.Iam unable to understand the concept of
modulation from the quantum physics point of view.Firstly what happens
to the energy/wave when it gets modulated?
amplitude modulation is easy, especially if you use digital on/off
levels of amplitude. Fire a continuous beam of light from transmitter
to receiver, then impose signal by waving a piece of cardboard in the
light beam according to your data ("100110010111" whatever). From QM
point of view, each "1" may contain a billion photons, each "0" may
contain ten. The energy is obviously going up and down with time due to
the modulation, and the receiver can tell the difference and
reconstruct the signal.
All the time I get the response theoretically in terms of change in
waves' shape.
I hope you're not trying to modulate a single particle wavefunction.
But how is it going to help?Can't a simple trans./recv. ckt not
suffice?
be a bit more specific here - a simple trans/recv circuit does suffice,
intermediated by the em waves which actually do the travelling from T
to R.
br
.
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| User: "krishna" |
|
| Title: Re: electromagnetism |
09 Nov 2005 02:17:55 AM |
|
|
hi list,
Thank you all for your explanation.This has triggered some more
ideas in me.The analogy of light beam and cardboard was great.Can I get
similar analogies for frequency and phase modulation techniques?
Thank you.
cheers-
kaushal.
.
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| User: "Dr Photon" |
|
| Title: Re: electromagnetism |
09 Nov 2005 06:43:32 AM |
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krishna wrote:
Can I get
similar analogies for frequency and phase modulation techniques?
Frequency modulation can also be described easily, again especially if
you go to the extreme and just modulate in 1s and 0s:
In this case send Blue for "1" and Red for "0".
Now each 1 or 0 can have the same power, maybe 1 mW each, but the
frequency is different.
Phase modulation is trickier - here maybe you need to visualise the
actual waviness of the wave, I'll try as follows:
You know that when two waves of the same frequency interfere, they can
interfere constructively or destructively. This depends on the relative
"phase" of the two waves, whether they are in phase or out of phase. So
to transmit a "1" or "0", have two waves - one wave is the usual
continuous sine wave, but the other wave has certain sections phase
shifted in-phase or out-of-phase according to whether it is encoding a
1 or 0. So when the two waves interfere, sometimes there will be
constructive interference, sometimes there will be destructive
interference along their length. Now only transmit the one wave which
has the phase shifts in it. At the receiver, this will be compared to a
continuous sine wave which the receiver has generated on his/her own,
and the constructive/destructive interference is easy to measure.
All the above explanations were digital 1s and 0s because they are
easiest to visualise, but the analogue case just involves intermediate
values. So for analogue amplitude modulation, just stick the cardboard
into the beam a little bit, so that reduces the amplitude a little bit,
etc.
regards,
br
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| User: "krishna" |
|
| Title: Re: electromagnetism |
10 Nov 2005 12:41:38 AM |
|
|
Hi Dr.Photon,
Thank you for the response.Kindly find the reply embedded:
Dr Photon wrote:
krishna wrote:
Can I get
similar analogies for frequency and phase modulation techniques?
Frequency modulation can also be described easily, again especially if
you go to the extreme and just modulate in 1s and 0s:
In this case send Blue for "1" and Red for "0".
This means whatever is my data it is converted interms of blues and
reds.
if the data is digital then it is one-one mapping.That is 1 for blue
and 0 for red.If the data is analog,is it still many to 'two'
mapping?ie,any level of voltage/current to either red/blue?I mean its a
bit confusing.Can you please elaborate this.
Now each 1 or 0 can have the same power, maybe 1 mW each, but the
frequency is different.
Phase modulation is trickier - here maybe you need to visualise the
actual waviness of the wave, I'll try as follows:
You know that when two waves of the same frequency interfere, they can
interfere constructively or destructively. This depends on the relative
"phase" of the two waves, whether they are in phase or out of phase. So
to transmit a "1" or "0", have two waves - one wave is the usual
continuous sine wave, but the other wave has certain sections phase
shifted in-phase or out-of-phase according to whether it is encoding a
1 or 0. So when the two waves interfere, sometimes there will be
constructive interference, sometimes there will be destructive
interference along their length. Now only transmit the one wave which
has the phase shifts in it. At the receiver, this will be compared to a
continuous sine wave which the receiver has generated on his/her own,
and the constructive/destructive interference is easy to measure.
*****>>>>
The above explanation ,I cud get it to large extent.I repeat it in my
words,pl correct me if it is wrong:The core idea is change a standard
sine wave(Accepted at both sender and receiver) based on the concept of
constructive and destructive interference patterns and release it to
the receiver.The reciver will observe the wave w.r.t the standard wave
that she has and understand the difference as data/the constructive
interfefence occurance as 1 and destructive interference occurance as
0,and hence extract the data.
In terms of energy:
Eneregy in the form of compressions and rarefractions would try to
reach the reciver,if we :
change the strength of this energy transmitted,it is amplitutde
modulation
change the rate at which energy is transmitted,it is frequency
modulation
change when the crests/troughs occur, it is phase modulation.
Just because both sender and reciver have a common/standard wave for
reference
we are opting for these kinds of modulation.
kindly coorect the above statements.
*****>>>>
All the above explanations were digital 1s and 0s because they are
easiest to visualise, but the analogue case just involves intermediate
values. So for analogue amplitude modulation, just stick the cardboard
into the beam a little bit, so that reduces the amplitude a little bit,
etc.
regards,
br
cheers-
kaushal.
.
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| User: "Dr Photon" |
|
| Title: Re: electromagnetism |
10 Nov 2005 04:09:27 AM |
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|
Krishna wrote:
Dr Photon wrote:
krishna wrote:
Can I get
similar analogies for frequency and phase modulation techniques?
Frequency modulation can also be described easily, again especially if
you go to the extreme and just modulate in 1s and 0s:
In this case send Blue for "1" and Red for "0".
This means whatever is my data it is converted interms of blues and
reds.
if the data is digital then it is one-one mapping.That is 1 for blue
and 0 for red.If the data is analog,is it still many to 'two'
mapping?ie,any level of voltage/current to either red/blue?I mean its a
bit confusing.Can you please elaborate this.
for analog transmission, use the colours in between red and blue
continuously, so for example you may have
red-yellow-red-orange-blue-green-... etc, with smooth variation from
one to the other, according to the signal to be sent.
Now each 1 or 0 can have the same power, maybe 1 mW each, but the
frequency is different.
Phase modulation is trickier - here maybe you need to visualise the
actual waviness of the wave, I'll try as follows:
[snip]
*****>>>>
The above explanation ,I cud get it to large extent.I repeat it in my
words,pl correct me if it is wrong:The core idea is change a standard
sine wave(Accepted at both sender and receiver) based on the concept of
constructive and destructive interference patterns and release it to
the receiver.The reciver will observe the wave w.r.t the standard wave
that she has and understand the difference as data/the constructive
interfefence occurance as 1 and destructive interference occurance as
0,and hence extract the data.
that's it
In terms of energy:
Eneregy in the form of compressions and rarefractions
not for EM waves. Compression/rarefaction is for longitudinal waves
such as sound waves. EM waves have amplitude (=>photon number),
frequency, phase and polarisation (you can also use polarisation
modulation).
would try to
reach the reciver,if we :
change the strength of this energy transmitted,it is amplitutde
modulation
"strength" of energy is not a good expression - actually it is rate at
which energy is sent, ie power
change the rate at which energy is transmitted,
it is frequency
modulation
no, rate of energy is power, which is used in AM. FM uses rate of
peaks/troughs transmitted, the power can be the same.
change when the crests/troughs occur,
it is phase modulation.
pretty much, if you interpret your sentence correctly. But remember
that frequency modulation also changes when the crests/troughs occur.
So in this sense FM and PhM are quite similar. However, they are
different in that if you send "111111" with FM, you have more
crests/troughs than if you send "000000", while in PhM you have the
same number of crests/troughs, but at a different time position.
Just because both sender and reciver have a common/standard wave for
reference
we are opting for these kinds of modulation.
yes, they need to agree beforehand what the communication channel
parameters are going to be.
kindly coorect the above statements.
cheers-
kaushal.
no problem.
I note in your OP you ask "I am unable to understand the concept of
modulation from the quantum physics point of view". Basically it
doesn't change much. The amplitude corresponds to photon number, but
the wavelength may actually need reinterpreting. Feynman seemed to want
to get away from the whole wave story. Check out
http://www.vega.org.uk/video/subseries/8
where he describes QM in terms of particles which interfere according
to little clocks they carry with them (though that is not the right
language, watch the videos to get a better understanding). This
recreates all the wave behaviour, but without the waves (!).
br
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| User: "krishna" |
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| Title: Re: electromagnetism |
14 Nov 2005 01:26:24 AM |
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Hi Dr.Photon,
Thanks a lot for your explanation.I think these
points have to be read between lines.The link sent is not a video
link.Can you suggest me a link/book that gives the kind of treatment
Iam looking for.Should I read more of electromagnetic nature of the
light to understand this better?Pl suggest me.Once again thank you list
for the help.
-kaushal.
.
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| User: "Dr Photon" |
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| Title: Re: electromagnetism |
14 Nov 2005 10:28:49 AM |
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krishna wrote:
Hi Dr.Photon,
Thanks a lot for your explanation.I think these
points have to be read between lines.The link sent is not a video
link.
click on the pictures at the left, or the text beside the pictures in
the middle of the page. They link to the following streaming video -
http://www.vega.org.uk/video/programme/45
http://www.vega.org.uk/video/programme/46
http://www.vega.org.uk/video/programme/47
http://www.vega.org.uk/video/programme/48
Can you suggest me a link/book that gives the kind of treatment
Iam looking for.
click around on
http://en.wikipedia.org/wiki/Modulation
for the classical modulation techniques. I'm not sure where to point
you for a QM description, engineers tend to think classically (up to
Maxwell's equations), and physicists consider modulation an engineering
problem :)
Should I read more of electromagnetic nature of the
light to understand this better?Pl suggest me.
The basic modulations only involve sine waves, one doesn't even need
for them to be "electromagnetic" waves. Depends on how far you want to
go. Sounds like you need a course in electrical/electronic engineering,
followed by a course in QM. But I appreciate that probably doesn't help
much right now :(
Apart from Wikipedia as a learning resource, Hyperphysics is v. good
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
and has sub-pages such as
http://hyperphysics.phy-astr.gsu.edu/hbase/audio/bcast.html
Once again thank you list
for the help.
-kaushal.
br
.
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| User: "Black Knight" |
|
| Title: Re: electromagnetism |
14 Nov 2005 12:10:16 PM |
|
|
"Dr Photon" <brendan.roycroft@nmrc.ie> wrote in message
news:1131985729.139705.279360@g47g2000cwa.googlegroups.com...
krishna wrote:
Hi Dr.Photon,
Thanks a lot for your explanation.I think these
points have to be read between lines.The link sent is not a video
link.
click on the pictures at the left, or the text beside the pictures in
the middle of the page. They link to the following streaming video -
http://www.vega.org.uk/video/programme/45
http://www.vega.org.uk/video/programme/46
http://www.vega.org.uk/video/programme/47
http://www.vega.org.uk/video/programme/48
Can you suggest me a link/book that gives the kind of treatment
Iam looking for.
click around on
http://en.wikipedia.org/wiki/Modulation
for the classical modulation techniques. I'm not sure where to point
you for a QM description, engineers tend to think classically (up to
Maxwell's equations), and physicists consider modulation an engineering
problem :)
Should I read more of electromagnetic nature of the
light to understand this better?Pl suggest me.
The basic modulations only involve sine waves, one doesn't even need
for them to be "electromagnetic" waves. Depends on how far you want to
go. Sounds like you need a course in electrical/electronic engineering,
followed by a course in QM. But I appreciate that probably doesn't help
much right now :(
Apart from Wikipedia as a learning resource,
Wackypedia can be written by ANY moron.
It statements concerning the postulates of SR are hopelessly wrong.
Androcles.
.
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| User: "Orion" |
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| Title: Re: electromagnetism |
15 Nov 2005 07:25:40 AM |
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The Bohr model of the atom is flawed. It doesn't explain why most of
the hydrogen spectrum is black:
http://upload.wikimedia.org/wikipedia/en/4/4c/Emission_spectrum-H.png
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| User: "krishna" |
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| Title: Re: electromagnetism |
15 Nov 2005 07:20:21 AM |
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Hi list,
Thanks a lot for all your suggestions and directions.The
interaction was enlightening.Special thanks to Dr.Photon and Black
knight.
cheers-
kaushal.
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