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Fw: communication concepts ??

 

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Here is a high-level explantion:
?
Sound is nothing more than compressions and decompressions of air.? Look at a speaker and?think of the way if pulsates back and forth.? This is producing these compressions and decompressions.? Since there is nothing to compress in a vacuum, sound cannot travel through it.
?
Electromagnetic waves are different.? These are not compressions and decompressions (of air at least).? In fact, no-one truly knows who the electromagnetic waves really work.? They can travel through a vacuum at the speed of light (3 * 10^ 8 m/s).?
?
Now, to get an idea of how sound is converted to electrical impulses, think of this scenerio.? Think of a big woofer speaker and remember how it works.? In its simplicity, it is a magnet moving back and forth in a magnetic field.? Now reverse this and think of this woofer as a microphone (although this would be a terrible microphone, but it demonstrates the principle nevertheless).? As I talk into this woofer, I am sending compresssions and decompressions of air which will move the woofer back and forth.? This moving of the woofer, will cause the magnet to move back and forth, thus generating alternating current.? This current is a representation of sound.? You can amplify this and then send it back to another speaker where it will produce the same back and forth movement and therefore produce the same compressions and decompressions of air (sound).
?
Radio waves are?electromagnetic waves.? A radio transmitter will simply take this alternating current and mix it up with an electromagnetic wave.? AM is short for amplitude modulation, and FM short for frequency modulation.? These are 2 different ways to combine AC and an electromagnetic wave, there are more however.? The receiver will then have to remove the electromagnetic?wave to recover the original AC signal.?
?
Bandwidth refers to the amount of data that can be transmitted over a medium.? In this case, it would be the frequency range (difference between highest and lowest frequencies transmitted).? I may be wrong, but when someone refers to purchasing bandwidth, I think they are referring to purchasing a licence to broadcast on a specific frequency.
?
Shaun Phelps
?
?
?
?
?

----- Original Message -----
Sent: Sunday, October 28, 2001 2:27 AM
Subject: [Electronics_101] Fw: communication concepts ??


hello, could anyone explain me the following ?? 1. how do the waves actually travel through air ? ( for eg. waves in a radio receiver ) 2. why dont these waves mix up ? how is it that same waves are received after tuning the receiver ?? 3. what does bandwidth actually mean ? what is meant by purchasing bandwidth? please suggest some links if possible ?? i am a student of engineering and have studied all types of modulation techniques in college theoretically ..but i always wonder or rather dont understand how one can actually transmit sound and pictures through air.. i want to clear my basics about all that .. please help me... practical answers are expected 'cos i know evrything in theory but still know nothing. rahul...

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Rahul Mulay
 

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hello, could anyone explain me the following ?? 1. how do the waves actually travel through air ? ( for eg. waves in a radio receiver ) 2. why dont these waves mix up ? how is it that same waves are received after tuning the receiver ?? 3. what does bandwidth actually mean ? what is meant by purchasing bandwidth? please suggest some links if possible ?? i am a student of engineering and have studied all types of modulation techniques in college theoretically ..but i always wonder or rather dont understand how one can actually transmit sound and pictures through air.. i want to clear my basics about all that .. please help me... practical answers are expected 'cos i know evrything in theory but still know nothing. rahul...

angtengchat
 

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Good question!
?

Sent: Sunday, October 28, 2001 4:27 PM
Subject: [Electronics_101] Fw: communication concepts ??
?
hello, could anyone explain me the following ?? 1. how do the waves actually travel through air ? ( for eg. waves in a radio receiver )
?
Sound waves cannot travel thru a vacumn. But I think light waves could, How is this done, could members tell us.
?
?2. why dont these waves mix up ? how is it that same waves are received after tuning the receiver ??
Different waves have different frequencies, thats why they dont mix up. We are able to receive because the receiver is tuned to that particular frequency.
?
Jim Purcell
 

angtengchat,
hello, could anyone explain me the following ?? 1. how do the waves actually travel through air ? ( for eg. waves in a radio receiver )?Sound waves cannot travel thru a vacumn. But I think light waves could, How is this done, could members tell us.

Of course light waves, and all electromagnet waves, i.e. radio, infra-red, ultra violet, gamma, etc. travel in a vacuum, that's how the sun's light and other waves can reach earth since there is no medium that we know of. There is great debate now as to whether light is a wave phenomenon, which requires a medium, or a particle phenomenon, which does not.
I can't tell you how these waves travel, if I could I could be famous.
But as for waves, the idea here is just like water waves. We see the
wave apparently traveling, but only the ripples travel, or appear to.
The water isn't moving much except up and down. Radio waves are
similar, but as I said, as far as we know there is no medium for them
to make waves in. They used to use a term, 'ether', to suggest that
there was some kind of mystical medium for the radio waves to trevel
through. The idea of ether has mostly disappeared, except that the
term is occasionally used, even referring to parts of the internet that
do not use wires, called the ethernet. Many words to say, we don't know.??2. why dont these waves mix up ? how is it that same waves are received after tuning the receiver ??
?Different waves have different frequencies, thats why they dont mix up. We are able to receive because the receiver is tuned to that particular frequency.

That's right and in fact when we WANT frequencies to mix together it takes a circuit that is non linear, i.e. that distorts the waves. When an AM radio receives a signal, the first circuit, the RF stage is tuned to
the signals frequency. Then the signal is converted to frequency that
is common to all signals being received called the 'intermediate frequency' or IF. This is usually 455 kHz. Whether the radio signal
was at 760 kHz,? a clear channel from my original home town of Detroit,
or 1130 kHz, a local talk show station in Milwaukee, they all are converted to 455 kHz. If the RF amplifiers were totally linear this
conversion wouldn't work.
?

Jim

[email protected]
 



I personally think that electro-magnetism is a force, therefore electromagnetic waves = electromagnetic force. and force can travel thru vacumn, thats how our rockets flies to the moon.

Rockets travel though space because for any force there is an equal but opposite force. Thrust from the rocket engine is focused in the opposite direction the rocket needs to go. ?This in turn forces the rocket forward. But the force itself is not propagated though the vacuum.

angtengchat
 

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----- Original Message -----
Sent: Sunday, October 28, 2001 1:25 PM
Subject: Re: [Electronics_101] Fw: communication concepts ??

Here is a high-level explantion:
?
Sound is nothing more than compressions and decompressions of air.? Look at a speaker and?think of the way if pulsates back and forth.? This is producing these compressions and decompressions.? Since there is nothing to compress in a vacuum, sound cannot travel through it.
?
Although I could visualise how sound waves propagate, just like dropping a 10cent coin into a pool of water, it is a serious mistake to use the above "speaker example" to illustrate how sound waves travelled because the above eg. has nothing to do with sound waves, it simply decode the the signal from the microphone (input), then subsequently encode it back to the speaker. This has nothing to do with sound except electro-magnetic waves.
?
Electromagnetic waves are different.? These are not compressions and decompressions (of air at least).? In fact, no-one truly knows who the electromagnetic waves really work.? They can travel through a vacuum at the speed of light (3 * 10^ 8 m/s).?
?
I personally think that electro-magnetism is a force, therefore electromagnetic waves = electromagnetic force. and force can travel thru vacumn, thats how our rockets flies to the moon.
?
Jim Purcell
 

angteng,

Sound is nothing more than compressions and decompressions of air.? Look at a speaker and?
?it is a serious mistake to use the above "speaker example" to illustrate how sound waves travelled because the above eg. has nothing to do with sound waves,

What is that comming from the speaker, prop wash. Of course it's sound. The pebble in the water example is used because it is very
visible. Sometimes speakers emit low frequency sound and that can
be seen AND heard.

it simply decode the the signal from the microphone

It's not so much a? decoding, although if you used that
concept the microphone encodes the sound and the speaker
decodes the signal back into sound. However, microphones
and speakers are transducers, they convert sound, i.e.
acoustics, to electrical voltage so that the input circuit can
amplify it. The speaker then converts the amplified elecrical
signal back into acoustic sound.
?I personally think that electro-magnetism is a force, therefore electromagnetic waves = electromagnetic force. and force can travel thru vacumn, thats how our rockets flies to the moon.

What is a force. There are lots of them, electrical force, electromotive
force, gravity, magnetic force.? Waves do not consist of particles traveling through space, but of changes in the medium which in such a
way that it seems like particles are traveling. Of course that seem to
break down when we get to a vacuum because em waves will travel in a
vacuum. There is a great dialog among physists about waves vs. particle
motion. I don't pretend to understand it at their level, I just know it
because of an interesting PBS special a few years ago.

Jim
angtengchat
 

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?
----- Original Message -----
Sent: Monday, October 29, 2001 8:48 AM
Subject: Re: [Electronics_101] Fw: communication concepts ??
I personally think that electro-magnetism is a force, therefore electromagnetic waves = electromagnetic force. and force can travel thru vacumn, thats how our rockets flies to the moon.
Rockets travel though space because for any force there is an equal but opposite force. Thrust from the rocket engine is focused in the opposite direction the rocket needs to go. ?This in turn forces the rocket forward. But the force itself is not propagated though the vacuum.
Talking about force, I?wonder if a rocket could fly across a vacumn, which does not have anything at all. I just wonder how could force produce motion if there's no friction for it to force a motion.
?
Is outer space a vacumn?
Jim Purcell
 

angtengchat,
Talking about force, I wonder if a rocket could fly across a vacumn, which does not have anything at all.

They already have, to the moon, mars and beyond. And yes, as far as we know space is a vacuum.

I just wonder how could force produce motion if there's no friction for it to force a motion.

Unlike propellers or jet planes, rockets provide their own 'force', when the propellent is pushed out of the tail the equal and opposite force propells the rocket in the opposite direction, at least as long as the
fuel lasts.? As an aside, popular si fi shows like Star Trek do a disservice to peoples understanding of science vis a vis motion
through space. First off, most of the time the rockets are turned
off. And if you continue to expell the rocket gases the speed of
the object, i.e. ship, would continue to increase. AND the fuel
would be expended very soon. Second, they often talk about a
ship being 'dead in the water' after the engines stop. Unless
they fire engines in the opposite direction the ship will merely
continue in the last direction it was traveling. There are more
but one of the worst, is when we see external shots of the
ships and hear their sound. Since space is a vacuum the sound
could not be heard, even if the viewer were out there unprotected
by a ship. Of course I know that drama often dictates that
science take a back seat. Those cannons in Star Wars are far
more dramatic when they recoil like WW II cannon.

Jim

d nixon
 

Outer space is not a total vacuum, but it's pretty dang close. As far as rockets go...

There doesn't have to be anything for the rocket to push against. Remember..."For every action there is an equal an opposite reaction." So as long as the rocket pushes *something* out the back it will move forward.

Rockets are different that propellered airplanes. Props must have something to push, rockets generate thrust through chemical reactions.

-Mike



From: "angtengchat" <angtengchat@...>
Reply-To: Electronics_101@...
To: <Electronics_101@...>
Subject: Re: [Electronics_101] Fw: communication concepts ??
Date: Mon, 29 Oct 2001 12:10:52 +0800


----- Original Message -----
From: aseesf4@...
To: Electronics_101@...
Sent: Monday, October 29, 2001 8:48 AM
Subject: Re: [Electronics_101] Fw: communication concepts ??
I personally think that electro-magnetism is a force, therefore electromagnetic waves = electromagnetic force. and force can travel thru vacumn, thats how our rockets flies to the moon.
Rockets travel though space because for any force there is an equal but opposite force. Thrust from the rocket engine is focused in the opposite direction the rocket needs to go. This in turn forces the rocket forward. But the force itself is not propagated though the vacuum.
Talking about force, I wonder if a rocket could fly across a vacumn, which does not have anything at all. I just wonder how could force produce motion if there's no friction for it to force a motion.

Is outer space a vacumn?



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[email protected]
 

Hi,
About the question "why waves don't mix up?"

Why this is putting it rather crudely but ... WAVES DO MIX UP!! What
happens is that after modulation of sound or picture, we generate what
is called as frequency band. The band is centered at the modulation
carrier frequency chosen, that is the tuning frequency of your radio
set.

Now suppose this band of frequencies is located from say 1.5MHz to
2.5MHz then there is no reason why the NOISE frequencies lying in this
band won't mix up.

Secondly, if somebody in some other station also moduates the band
with the same carrier frequency your station will get blocked if his
station is quite strong. THIS IS THE EXAMPLE OF WAVES GETTING MIXED
UP.

Practically it doesn't happen becoz every station has a dedicated band
of its own and cannot go beyond it.

regds,
Aditya
Jim Purcell
 

adity,

About the question "why waves don't mix up?"

Why this is putting it rather crudely but ... WAVES DO MIX UP!!
The original issue was whether various natural e.m. waves, i.e
light, etc. don't mix. And they generally don't I think. What
you are talking about is modulation, as with an AM transmitter.
And even then the carrier wave is preserved. You have the
carrier wave, the frequency that the station advertises, plus
multiple side bands that are at frequencies equal to carrier
+/- the audio frequency. I recall my office mate at the
college where I taught, the same one who told me that
a capacitors charge resides in the dielectric rather than
the plates, by the way, was surprised when I told him
that an AM radio station could modulate up to +/-
15 kHz from the carrier. He thought that the ten kHz
spacing of radio station's meant that they were limited
to +/- 5 kHz. So e.m. waves can get mixed or they can
stay separate, depending on the conditions. It is my
understanding that the mixing requires non linearity
of the medium or device through which they pass, i.e.
a vacuum tube, a transistor, even a diode.

Jim
Doug Hale
 

Mixers are just analog multipliers, that is about as linear as it gets.

The Radio ether is just one big summing junction (with distance related attenuation). It is not exactly like there is a 50Mhz signal, and a 50.5 Mhz signal, and a 51Mhz signal, ...There is only one signal - that is the sum of all the signals being transmitted. That signal has a 50Mhz component, a 50.5Mhz component, a 51Mhz component, ...

Let me show you an example of this:
A square wave is a single signal - or waveform. Yet it consist of many frequency componts.
The equation for the voltage of the square wave at any given time is actually a summation of all the frequencies of the square wave. The equation is:
sin(wt) - sin(3wt)/3 + sin(5wt)/5 - sin(7wt)/7 + sin(9wt)/9 - sin(11wt)/11 ...

w = 2 Pi f
Pi is 3.141576...
f is the base frequency of the square wave
t is time

The ... at the end of the equation indicates that this is an infinate series - it goes on for ever.

Now, if I were to build a filter that only allows sin(7wt) to pass, I would get a sine wave that is 7 times the frequency of the square wave.

This is call fourier analysis - which is frequency domain in stead of time domain.
In time domain, we concern our selves with what a voltage or current is at a given time.
In frequency domain, we concern ourselves with the current or voltage at a given frequency.

So when we talk of the radio ether having different frequencys - a 50Mhz, a 50.5Mhx, a 51Mz, ...
we aren't actually that far off - we are just talking in frequency domain terms instead of time domain terms.
Why do we use frequency domain insead of time domain? I bet most of you have not yet got your head around the square wave example but you all have a working knowledge of radios - you can tune them to a station of your choice. We use frequency domain because it is much easier.

If you want to prove the above square wave example to yourself, search the web for a program called GNUPLOT. Install it and play with it.

Doug Hale




Jim Purcell wrote:

adity,

About the question "why waves don't mix up?"

Why this is putting it rather crudely but ... WAVES DO MIX UP!!
The original issue was whether various natural e.m. waves, i.e
light, etc. don't mix. And they generally don't I think. What
you are talking about is modulation, as with an AM transmitter.
And even then the carrier wave is preserved. You have the
carrier wave, the frequency that the station advertises, plus
multiple side bands that are at frequencies equal to carrier
+/- the audio frequency. I recall my office mate at the
college where I taught, the same one who told me that
a capacitors charge resides in the dielectric rather than
the plates, by the way, was surprised when I told him
that an AM radio station could modulate up to +/-
15 kHz from the carrier. He thought that the ten kHz
spacing of radio station's meant that they were limited
to +/- 5 kHz. So e.m. waves can get mixed or they can
stay separate, depending on the conditions. It is my
understanding that the mixing requires non linearity
of the medium or device through which they pass, i.e.
a vacuum tube, a transistor, even a diode.

Jim



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Electronics_101-unsubscribe@...


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[email protected]
 

Hi,

You said,
was surprised when I told him
that an AM radio station could modulate up to +/-
15 kHz from the carrier. He thought that the ten kHz
spacing of radio station's meant that they were limited
to +/- 5 kHz.
I also cannot wonder less. How is that possible?? Please explain.

Thanx,
Aditya
Jim Purcell
 

adityan,

was surprised when I told him
that an AM radio station could modulate up to +/-
15 kHz from the carrier. He thought that the ten kHz
spacing of radio station's meant that they were limited
to +/- 5 kHz.
I also cannot wonder less. How is that possible??
Well, there are two factors, what the modulation
frequencies the transmitter is capable of and what
bandwidth the FCC allows. Both are +/- 15 kHz in
most cases. How can this be, simple, stations are
never assigned frequencies close enough to interfere.
You won't have one station at 1000 kHz and a near
by one at 1010 kHz or 990 kHz, and probably none
at 1020 or 980.

Jim
angtengchat
 

Seeing how you could do calculations and your detailed explanation, I
regretted that I did not have a formal electrical-electronic education.

Sigh!

----- Original Message -----
From: "Doug Hale" <doughale@...>
To: <Electronics_101@...>
Sent: Thursday, November 01, 2001 12:07 AM
Subject: Re: [Electronics_101] Re: Fw: communication concepts ??


Mixers are just analog multipliers, that is about as linear as it gets.

The Radio ether is just one big summing junction (with distance related
attenuation). It is not exactly like there is a 50Mhz signal, and a 50.5
Mhz signal, and a 51Mhz signal, ...There is only one signal - that is
the sum of all the signals being transmitted. That signal has a 50Mhz
component, a 50.5Mhz component, a 51Mhz component, ...

Let me show you an example of this:
A square wave is a single signal - or waveform. Yet it consist of
many frequency componts.
The equation for the voltage of the square wave at any given time
is actually a summation of all the frequencies of the square wave. The
equation is:
sin(wt) - sin(3wt)/3 + sin(5wt)/5 - sin(7wt)/7 + sin(9wt)/9 -
sin(11wt)/11 ...

w = 2 Pi f
Pi is 3.141576...
f is the base frequency of the square wave
t is time

The ... at the end of the equation indicates that this is an infinate
series - it goes on for ever.

Now, if I were to build a filter that only allows sin(7wt) to pass,
I would get a sine wave that is 7 times the frequency of the square wave.

This is call fourier analysis - which is frequency domain in stead of
time domain.
In time domain, we concern our selves with what a voltage or
current is at a given time.
In frequency domain, we concern ourselves with the current or
voltage at a given frequency.

So when we talk of the radio ether having different frequencys - a
50Mhz, a 50.5Mhx, a 51Mz, ...
we aren't actually that far off - we are just talking in frequency
domain terms instead of time domain terms.
Why do we use frequency domain insead of time domain? I bet most of you
have not yet got your head around the square wave example but you all
have a working knowledge of radios - you can tune them to a station of
your choice. We use frequency domain because it is much easier.

If you want to prove the above square wave example to yourself, search
the web for a program called GNUPLOT. Install it and play with it.

Doug Hale




Jim Purcell wrote:

adity,

About the question "why waves don't mix up?"

Why this is putting it rather crudely but ... WAVES DO MIX UP!!
The original issue was whether various natural e.m. waves, i.e
light, etc. don't mix. And they generally don't I think. What
you are talking about is modulation, as with an AM transmitter.
And even then the carrier wave is preserved. You have the
carrier wave, the frequency that the station advertises, plus
multiple side bands that are at frequencies equal to carrier
+/- the audio frequency. I recall my office mate at the
college where I taught, the same one who told me that
a capacitors charge resides in the dielectric rather than
the plates, by the way, was surprised when I told him
that an AM radio station could modulate up to +/-
15 kHz from the carrier. He thought that the ten kHz
spacing of radio station's meant that they were limited
to +/- 5 kHz. So e.m. waves can get mixed or they can
stay separate, depending on the conditions. It is my
understanding that the mixing requires non linearity
of the medium or device through which they pass, i.e.
a vacuum tube, a transistor, even a diode.

Jim



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Doug Hale
 

I wouldn't let that stop me, I have the degree but I don't work in that field. I am completely self taught in the field I currently work in, and the one before that, and the one before that, ...

You can do ANYTHING, you just have to decide to pay the price. (study)

The key to electronics is math. Math is nothing more than a modeling language. It provides us with a way to model/describe natural behavior in an unambiguous may.

My formal training is mainly in Control Theory. My first job out of school was in computers. I learned digital electronics from Manufacture's data sheets and application notes - primarily Signetics because they gave them away instead of charging for them.

I got my BS in 1975 but I have never stopped learning. Learn from whatever source you can find. The web is full of stuff, course materials, data sheets, application notes, white papers, ... There are some good beginning books at the ubiquitous Radio Shack. I f there is a college or university near you, you can find some real good used text books - and actually the older the better. My favorite sources are still my OLD college texts (yep, I've still got them all).

But most of all, have fun and enjoy what you are doing, it makes overcoming the difficult thing that much more rewarding.


Doug Hale

angtengchat wrote:

Seeing how you could do calculations and your detailed explanation, I
regretted that I did not have a formal electrical-electronic education.

Sigh!
Jim Purcell
 

angtengchat,

Seeing how you could do calculations and your detailed explanation, I
regretted that I did not have a formal electrical-electronic education.
Self education is an alternative. That's how I got my initial training,
two home study courses. The second got me my FCC license and a job
in broadcasting. That was a good learning opportunity. A broadcaster
had to be jack of all trades and was seldom master of any of them.

Jim
angtengchat
 

You are a great man Doug! May I take this opportunity to wish you all the
best.

Although I've learnt many things myself, unfortunately I did not seek to
master them, I'm therefore a "Jack of many trades but master of none". DNA,
is a real thing, I doubt my characteristic will change.

The turn of the previous century ( 1899 to 1900's) saw a
tremendous-remarkable change, one that wipes out progress since the
existance of life, in the way mankind lived because of the discovery and
aggressive-scientific progress on the understanding of electricity.

Will there be another similar progress this century, depends on how
successful scientist persue and "tear apart" DNA, the study of life-science.
It's an un-imaginable thing to think of the integration of
electricity-electronic-artificial intelligence-DNA.

----- Original Message -----
From: "Doug Hale" <doughale@...>
To: <Electronics_101@...>
Sent: Thursday, November 01, 2001 11:38 PM
Subject: Re: [Electronics_101] Re: Fw: communication concepts ??


I wouldn't let that stop me, I have the degree but I don't work in that
field. I am completely self taught in the field I currently work in, and
the one before that, and the one before that, ...

You can do ANYTHING, you just have to decide to pay the price. (study)

The key to electronics is math. Math is nothing more than a modeling
language. It provides us with a way to model/describe natural behavior
in an unambiguous may.

My formal training is mainly in Control Theory. My first job out of
school was in computers. I learned digital electronics from
Manufacture's data sheets and application notes - primarily Signetics
because they gave them away instead of charging for them.

I got my BS in 1975 but I have never stopped learning. Learn from
whatever source you can find. The web is full of stuff, course
materials, data sheets, application notes, white papers, ... There are
some good beginning books at the ubiquitous Radio Shack. I f there is a
college or university near you, you can find some real good used text
books - and actually the older the better. My favorite sources are still
my OLD college texts (yep, I've still got them all).

But most of all, have fun and enjoy what you are doing, it makes
overcoming the difficult thing that much more rewarding.


Doug Hale

angtengchat wrote:

Seeing how you could do calculations and your detailed explanation, I
regretted that I did not have a formal electrical-electronic education.

Sigh!



To unsubscribe from this group, send an email to:
Electronics_101-unsubscribe@...



Your use of Yahoo! Groups is subject to

_________________________________________________________
Do You Yahoo!?
Get your free @yahoo.com address at

Jim Purcell
 

angtengchat,

Will there be another similar progress this century, depends on how
successful scientist persue and "tear apart" DNA, the study of life-science.
It's an un-imaginable thing to think of the integration of
electricity-electronic-artificial intelligence-DNA.
Too bad we can't do something about the terrible things humans do to each other.

That and the fact that some people seem far less able to deal with the evil they

encounter, without inflicting even more evil on other innocents.

Jim

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