Do a google search on "satellite_seminar.pdf." There will be two
sites that come up. Click on the princeton site which will download
the pdf document. Look on page 16 of that pdf document for an AM
demodulation algorithm. Look on page 17 for a JAVA implementation.
This algorithm works fine, because I have used it; however, you must
consider 1) the input audio signal format to be demodulated and 2) the
sample rate that you demodulate. Otherwise, your picture will look
like random garbage.
To briefly explain ...
1) I used an 8 bit WAV file to record the weather satellite audio
signal, so I had to subtract 127 from the WAV data before I applied
the AM demodulation algorithm.
2) each line has a visible image and an IR image. You must consider
your sample rate because you will want to toss some data; otherwise,
your image will be slanted.
After you get this working, you will probably want to use wxsat.
By the way, you really should try to understand the math!
Ken
Reply by Tom●October 13, 20032003-10-13
Ren� wrote:
> Steve wrote:
> > Having looked through countless websites and books, I've learnt loads,
> > but not what i'm looking for: An algorithm for AM demodulation... Can
> > anyone help?
>
> demodulation
>
> output = lowpass filter ( abs (input) )
>
> Ren�
A better way is to recover the original carrier and multiply it back into
the AM and then lowpas filter.
This is so-called synchronous demodulation.To recover the carrier you could
use a PLL or more crudely a hard limiter but the hard limiter is not a great
idea at low SNRs.
Tom
Reply by Jerry Avins●October 13, 20032003-10-13
Rune Allnor wrote:
> Jerry Avins <jya@ieee.org> wrote in message news:<bmbq5f$fs9$1@bob.news.rcn.net>...
>
>
>>Once I walked into a room filled with strangers, and was immediately
>>accosted: "You're an electrical engineer. Please fix the television." I
>>did. I replaces the battery in the remote with the cells in my pocket
>>flashlight. If course I carry a flashlight; don't you?
>
>
> In winter, yes. The pockets in my winter coats are large enough to hold
> the flashlight as well as the drawing pad and my pencils. My summer jackets
> only have room for the drawing kit. And where I am there's the midnight
> sun during summer, so I don't need the flashlight...
>
> Rune
I use my penlight mostly for looking into and under things, although it
was handy down in the depths of Mammoth Cave when a storm knocked out
the electricity powering the lights*.
Jerry
_________________________________________
* Before anyone asks, the guides all had flashlights, but we were strung
out in a narrow serpentine passage, and no light from either end of the
line came to us near the middle. The little light saved a claustrophobic
mother from freaking out in front of her pre-teen son.
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Rune Allnor●October 12, 20032003-10-12
Jerry Avins <jya@ieee.org> wrote in message news:<bmbq5f$fs9$1@bob.news.rcn.net>...
> Once I walked into a room filled with strangers, and was immediately
> accosted: "You're an electrical engineer. Please fix the television." I
> did. I replaces the battery in the remote with the cells in my pocket
> flashlight. If course I carry a flashlight; don't you?
In winter, yes. The pockets in my winter coats are large enough to hold
the flashlight as well as the drawing pad and my pencils. My summer jackets
only have room for the drawing kit. And where I am there's the midnight
sun during summer, so I don't need the flashlight...
Rune
Reply by Rune Allnor●October 12, 20032003-10-12
Jerry Avins <jya@ieee.org> wrote in message news:<bmbq5f$fs9$1@bob.news.rcn.net>...
> Once I walked into a room filled with strangers, and was immediately
> accosted: "You're an electrical engineer. Please fix the television." I
> did. I replaces the battery in the remote with the cells in my pocket
> flashlight. If course I carry a flashlight; don't you?
In winter, yes. The pockets in my winter coats are large enough to hold
the flashlight as well as the drawing pad and my pencils. My summer jackets
only have room for the drawing kit. And where I am there's the midnight
sun during summer, so I don't need the flashlight...
Rune
Reply by Jerry Avins●October 12, 20032003-10-12
Rune Allnor wrote:
> Jerry Avins <jya@ieee.org> wrote in message news:<bmamiu$e2d$3@bob.news.rcn.net>...
>
>>Rune Allnor wrote:
>>
>>
>>> ... It's not fun when I have to tell
>>>people that I'm only an engineer who uses the rules of maths and physics,
>>>and not some sort of sorcerer.
>>>
>>>Rune
>>
>>But aren't those the same thing? Many think so!
>
>
> Unfortunately, you're right. The scary thing is *where* I find these
> kinds of thoughts:
>
> - The 40+ years (of experience) senior scientist who wanted to specify
> "60 degrees phase lag between the 20 Hz component and the 80 Hz component"
> in a steady-state multiple-lines narrow-band source. I managed to wave
> that one off.
>
[more scary stories]
>
> I can only guess, but what I think I may be doing differently that these
> people (that may explain my ridicilous "wizard" reputation), is paying
> attention to detail. To not take anything for granted, not accept something
> as "easy" or "irrelevant" until I've cheked things out. To try to think the
> problem through. To try to find out what others have tried and how those
> attempts went.
>
> But that's what basic engineering training is all about, isn't it?
>
> Rune
Maybe we need to be wizards to get it right, but I think all it takes is
recognizing how east it is to be wrong, and finding error embarrassing
if not shameful (depending on circumstances). I visited friends last
night who anxiously awaited my arrival because the CD player wouldn't
work. The drawer wouldn't stay closed. Why me? I had never seen the
thing. Of course, I fixed it easily. The TV remote was lying next to the
player and stuck on. Moving it out of the way so I had more room to peek
was all the fix needed. Do they believe I fixed it by accident? Of
course not. I went to high school with these people, and they know me to
have been doing that sort if thing for a long time.
Once I walked into a room filled with strangers, and was immediately
accosted: "You're an electrical engineer. Please fix the television." I
did. I replaces the battery in the remote with the cells in my pocket
flashlight. If course I carry a flashlight; don't you?
Get used to it. By the standards of most of the boobs out there, doctors
(of all fields), lawyers, CEOs, you ARE a wizard. Grin and bear it.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Rune Allnor●October 12, 20032003-10-12
Jerry Avins <jya@ieee.org> wrote in message news:<bmamiu$e2d$3@bob.news.rcn.net>...
> Rune Allnor wrote:
>
> > ... It's not fun when I have to tell
> > people that I'm only an engineer who uses the rules of maths and physics,
> > and not some sort of sorcerer.
> >
> > Rune
>
> But aren't those the same thing? Many think so!
Unfortunately, you're right. The scary thing is *where* I find these
kinds of thoughts:
- The 40+ years (of experience) senior scientist who wanted to specify
"60 degrees phase lag between the 20 Hz component and the 80 Hz component"
in a steady-state multiple-lines narrow-band source. I managed to wave
that one off.
- The 10+ years (of experience) seismic processor who found the sound
velocity in the bedrock *immediately below* a high-velocity geologic
layer by means of refraction seismics. A trivial property of such analysis
is that the sound speed must be strictly *increasing* with depth. I found
a possible explanation for this measurement which, if correct, could be
the key to understand the acoustics of that whole geographical region.
- The head of the Sig Proc department at an international research facility
who asked me why I bothered with all that high-res analysis when a
simple zero-padding + FFT of my data would resolve the features I was
looking for. I was very glad *not* to be offered a job on that facility
after that meeting.
- The internationally renowned scientist who did not understand why I was
so conserned about symmetry properties in the 2D DFT since "it's only
the positive frequencies that go into the inverse transform". I was
very cautious in how I read his journal articles after that.
- The scientist who was overly concerned about not being able to make
computational models that were able to generate as strong Rayleigh waves
(ground roll) as measured in real life, when analyzing the muzzle blast
of heavy artillery. I knew the Rayleigh waves well enough to see other
possible excitation mechanisms in that experimental setup. No basic text
on Rayleigh waves fail to mention these excitation mechanisms.
- The 40+ years (of experience) scientist who asked for my array processing
codes for analyzing arrays with logarithmic element spacing. "If you can't
give it out, I'll just pick equidistant elements in the array and use
standard FFTs". Anyone are free to try to pick an equidistant subsequence
of three or more elements out of a series that goes as
D_n = D_0*K^(n-1) n=1,2, 3,...
where K =/= 1.
All these are different people at different facilities, but make mistakes
I find utterly trivial. "Why bother?" you may ask, "Everybody make mistakes.
It's not unheard of that even a certain Rune comes with corrections to his
own posts on comp.dsp". Well, it's a consistent pattern: People who really
should know better make the most trivial mistakes. The real problem, though,
is that they evidently are not open to neither accept the mistakes or
correct them.
I can only guess, but what I think I may be doing differently that these
people (that may explain my ridicilous "wizard" reputation), is paying
attention to detail. To not take anything for granted, not accept something
as "easy" or "irrelevant" until I've cheked things out. To try to think the
problem through. To try to find out what others have tried and how those
attempts went.
But that's what basic engineering training is all about, isn't it?
Rune
Reply by Rune Allnor●October 12, 20032003-10-12
Jerry Avins <jya@ieee.org> wrote in message news:<bmamiu$e2d$3@bob.news.rcn.net>...
> Rune Allnor wrote:
>
> > ... It's not fun when I have to tell
> > people that I'm only an engineer who uses the rules of maths and physics,
> > and not some sort of sorcerer.
> >
> > Rune
>
> But aren't those the same thing? Many think so!
Unfortunately, you're right. The scary thing is *where* I find these
kinds of thoughts:
- The 40+ years (of experience) senior scientist who wanted to specify
"60 degrees phase lag between the 20 Hz component and the 80 Hz component"
in a steady-state multiple-lines narrow-band source. I managed to wave
that one off.
- The 10+ years (of experience) seismic processor who found the sound
velocity in the bedrock *immediately below* a high-velocity geologic
layer by means of refraction seismics. A trivial property of such analysis
is that the sound speed must be strictly *increasing* with depth. I found
a possible explanation for this measurement which, if correct, could be
the key to understand the acoustics of that whole geographical region.
- The head of the Sig Proc department at an international research facility
who asked me why I bothered with all that high-res analysis when a
simple zero-padding + FFT of my data would resolve the features I was
looking for. I was very glad *not* to be offered a job on that facility
after that meeting.
- The internationally renowned scientist who did not understand why I was
so conserned about symmetry properties in the 2D DFT since "it's only
the positive frequencies that go into the inverse transform". I was
very cautious in how I read his journal articles after that.
- The scientist who was overly concerned about not being able to make
computational models that were able to generate as strong Rayleigh waves
(ground roll) as measured in real life, when analyzing the muzzle blast
of heavy artillery. I knew the Rayleigh waves well enough to see other
possible excitation mechanisms in that experimental setup. No basic text
on Rayleigh waves fail to mention these excitation mechanisms.
- The 40+ years (of experience) scientist who asked for my array processing
codes for analyzing arrays with logarithmic element spacing. "If you can't
give it out, I'll just pick equidistant elements in the array and use
standard FFTs". Anyone are free to try to pick an equidistant subsequence
of three or more elements out of a series that goes as
D_n = D_0*K^(n-1) n=1,2, 3,...
where K =/= 1.
All these are different people at different facilities, but make mistakes
I find utterly trivial. "Why bother?" you may ask, "Everybody make mistakes.
It's not unheard of that even a certain Rune comes with corrections to his
own posts on comp.dsp". Well, it's a consistent pattern: People who really
should know better make the most trivial mistakes. The real problem, though,
is that they evidently are not open to neither accept the mistakes or
correct them.
I can only guess, but what I think I may be doing differently that these
people (that may explain my ridicilous "wizard" reputation), is paying
attention to detail. To not take anything for granted, not accept something
as "easy" or "irrelevant" until I've cheked things out. To try to think the
problem through. To try to find out what others have tried and how those
attempts went.
But that's what basic engineering training is all about, isn't it?
Rune
Reply by Jerry Avins●October 12, 20032003-10-12
Rune Allnor wrote:
> ... It's not fun when I have to tell
> people that I'm only an engineer who uses the rules of maths and physics,
> and not some sort of sorcerer.
>
> Rune
But aren't those the same thing? Many think so!
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Rune Allnor●October 11, 20032003-10-11
Jerry Avins <jya@ieee.org> wrote in message news:<bm748b$c59$1@bob.news.rcn.net>...
> Actually, succeeding can hurt.
It sure can. For reasons unclear to me, I apparently had gained a
reputation as some sort of "signal processing wizard" amongst the
people around me when I wrote that PhD thesis of mine. As I have
commented upon before, I never did anything I don't expect any
other DSP engineer to be able to if given similar time and resources.
Anyway, after my dissertation I have not been able to find a decent,
workable project. All those more or less weird things, based more on
wishful thinking than anything else, seem to come my way. "If anyone
can do it, Rune can." I am not sure if I ever heard it spoken out, but
it seems to be the general attitude. It's not fun when I have to tell
people that I'm only an engineer who uses the rules of maths and physics,
and not some sort of sorcerer.
Rune