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From: species8350 on 19 Jan 2010 06:30
On Jan 18, 3:25 am, Rich Johnson <ri...(a)remove.this.tairedd.com>
wrote:
> On 1/8/2010 4:04 AM, species8350 wrote:
>
>
>
>
>
> > On Jan 7, 5:19 pm, Jeff Liebermann<je...(a)cruzio.com>  wrote:
> >> On Thu, 7 Jan 2010 03:58:50 -0800 (PST), species8350
>
> >> <not_here.5.species8...(a)xoxy.net>  wrote:
> >>> I know that the wifi signal is modulated.
>
> >> Yep.
>
> >>> Firstly, why does the signal need to be modulated.
>
> >> Because it's the modulation that carries the information (data).  No
> >> modulation, no data.
>
> >>> Secondly regarding g: why are ther so many coding systems used.
>
> >> The modulation method varies with the speed of transmission.  Slow
> >> speeds have greater range because they have a higher signal to noise
> >> ratio for a given signal level.  Higher speeds have progressively
> >> lower signal to noise ratios for the same signal level.  802.11g will
> >> try to negotiate and establish a modulation method that produces the
> >> highest data rate, without having the signal to noise ratio become so
> >> low that all that is being received are errors and garbage.  More
> >> simply, the different modulation methods trade transmission speed for
> >> error rate.  If the errors increase for some reason, the access point
> >> will slow things down until the error rate returns to a reasonable
> >> value.
>
> >> I guess you haven't looked at 802.11n, which as 77 modulation coding
> >> schemes.
> >> <http://www.airmagnet.com/assets/whitepaper/WP-802.11nPrimer.pdf>
> >> The faster you go, the more complexicated the mess.
>
> >> --
> >> Jeff Liebermann     je...(a)cruzio.com
> >> 150 Felker St #D    http://www.LearnByDestroying.com
> >> Santa Cruz CA 95060http://802.11junk.com
> >> Skype: JeffLiebermann     AE6KS    831-336-2558
>
> > Thanks for the response.
>
> > Is this a way of looking at modulation.
>
> > The data has to be transmitted, so it is converted into a wave. That
> > wave is the modulation.
>
> > So, at transmission point, the wave is created. At receiver point, it
> > is demodulated, that is, converted back into data.
>
> > The problem with this model is that it doesn't explain how the coding
> > schemes will vary, depending upon data rate and errors.
>
> > Thanks.
>
> Modulation:
>
> Baseband information is converted into electrical information.  That
> electrical information is then used to change a "carrier" in some way to
> convey the information.
>
> So, if you were using morse code, with it's dits and dahs.  You could
> simply turn the carrier on and off following the duration of the dit or
> the dah.
>
> This is the first way we conveyed information.  In essence, we varied
> the amplitude of the carrier.  Once we wanted to carry sound, we
> converted it into an electrical signals and used it to directly affect
> the amplitude of a carrier wave signal.  This was called Amplitude
> Modulation.  (AM)
>
> Another component of a carrier wave is frequency.  We could also vary it
> in accordance with an electrically converted audio information.  This is
> called Frequency Modulation.  (FM)
>
> Video signals, (in the USA) were impressed on to a carrier using AM.
> (Vestigal side band AM, but still AM).  Later schemes allowed the color
> information to be modulated onto a 3.58 MHz subcarrier, using the
> combination of phase (something a carrier also has) and AM.
>
> This is also how we have moved in data carriers.  Using a phase of a
> carrier and the amplitude of the carrier we can set up a scheme that
> allows multiple bits to be conveyed with a single phase/amplitude change.
>
> This is modulation.  Pure and simple.  Once we can convey
> information/data, we have other opportunities to set protocols for the
> transmission of data.  Here is where error correction and validation
> come into play.  In essence here we can control what a "packet" of data
> looks like and can use math to be sure the data is valid.  Also, we can
> sequence the data with it.
>
> Each thing is simple, put together very powerful.- Hide quoted text -
>
> - Show quoted text -

Thanks for responding.

I have no background in the subject and am a bit confused.

'Baseband information is converted into electrical information. That
electrical information is then used to change a "carrier" in some way
to
convey the information.'

What is 'Baseband information'.

How is it converted into electrical information?

How does the electrical information change a carrier. I assume that a
carrier is just another signal. Since the electrical information is a
signal in itself, why not just send that?

Excuse my ignorance, but if I don't ask, I 'll never learn.

Best wishes

S


From: Richard Johnson on 22 Jan 2010 15:53

"species8350" <not_here.5.species8350(a)xoxy.net> wrote in message
news:a7e096ef-4c98-4b1c-b091-2c3b23d6df8e(a)p8g2000yqb.googlegroups.com...
On Jan 18, 3:25 am, Rich Johnson <ri...(a)remove.this.tairedd.com>
wrote:
> On 1/8/2010 4:04 AM, species8350 wrote:
>
>
>
>
>
> > On Jan 7, 5:19 pm, Jeff Liebermann<je...(a)cruzio.com> wrote:
> >> On Thu, 7 Jan 2010 03:58:50 -0800 (PST), species8350
>
> >> <not_here.5.species8...(a)xoxy.net> wrote:
> >>> I know that the wifi signal is modulated.
>
> >> Yep.
>
> >>> Firstly, why does the signal need to be modulated.
>
> >> Because it's the modulation that carries the information (data). No
> >> modulation, no data.
>
> >>> Secondly regarding g: why are ther so many coding systems used.
>
> >> The modulation method varies with the speed of transmission. Slow
> >> speeds have greater range because they have a higher signal to noise
> >> ratio for a given signal level. Higher speeds have progressively
> >> lower signal to noise ratios for the same signal level. 802.11g will
> >> try to negotiate and establish a modulation method that produces the
> >> highest data rate, without having the signal to noise ratio become so
> >> low that all that is being received are errors and garbage. More
> >> simply, the different modulation methods trade transmission speed for
> >> error rate. If the errors increase for some reason, the access point
> >> will slow things down until the error rate returns to a reasonable
> >> value.
>
> >> I guess you haven't looked at 802.11n, which as 77 modulation coding
> >> schemes.
> >> <http://www.airmagnet.com/assets/whitepaper/WP-802.11nPrimer.pdf>
> >> The faster you go, the more complexicated the mess.
>
> >> --
> >> Jeff Liebermann je...(a)cruzio.com
> >> 150 Felker St #D http://www.LearnByDestroying.com
> >> Santa Cruz CA 95060http://802.11junk.com
> >> Skype: JeffLiebermann AE6KS 831-336-2558
>
> > Thanks for the response.
>
> > Is this a way of looking at modulation.
>
> > The data has to be transmitted, so it is converted into a wave. That
> > wave is the modulation.
>
> > So, at transmission point, the wave is created. At receiver point, it
> > is demodulated, that is, converted back into data.
>
> > The problem with this model is that it doesn't explain how the coding
> > schemes will vary, depending upon data rate and errors.
>
> > Thanks.
>
> Modulation:
>
> Baseband information is converted into electrical information. That
> electrical information is then used to change a "carrier" in some way to
> convey the information.
>
> So, if you were using morse code, with it's dits and dahs. You could
> simply turn the carrier on and off following the duration of the dit or
> the dah.
>
> This is the first way we conveyed information. In essence, we varied
> the amplitude of the carrier. Once we wanted to carry sound, we
> converted it into an electrical signals and used it to directly affect
> the amplitude of a carrier wave signal. This was called Amplitude
> Modulation. (AM)
>
> Another component of a carrier wave is frequency. We could also vary it
> in accordance with an electrically converted audio information. This is
> called Frequency Modulation. (FM)
>
> Video signals, (in the USA) were impressed on to a carrier using AM.
> (Vestigal side band AM, but still AM). Later schemes allowed the color
> information to be modulated onto a 3.58 MHz subcarrier, using the
> combination of phase (something a carrier also has) and AM.
>
> This is also how we have moved in data carriers. Using a phase of a
> carrier and the amplitude of the carrier we can set up a scheme that
> allows multiple bits to be conveyed with a single phase/amplitude change.
>
> This is modulation. Pure and simple. Once we can convey
> information/data, we have other opportunities to set protocols for the
> transmission of data. Here is where error correction and validation
> come into play. In essence here we can control what a "packet" of data
> looks like and can use math to be sure the data is valid. Also, we can
> sequence the data with it.
>
> Each thing is simple, put together very powerful.- Hide quoted text -
>
> - Show quoted text -

Thanks for responding.

I have no background in the subject and am a bit confused.

'Baseband information is converted into electrical information. That
electrical information is then used to change a "carrier" in some way
to
convey the information.'

What is 'Baseband information'.

How is it converted into electrical information?

How does the electrical information change a carrier. I assume that a
carrier is just another signal. Since the electrical information is a
signal in itself, why not just send that?

Excuse my ignorance, but if I don't ask, I 'll never learn.

Best wishes

S

Baseband information is the electrical representation of the information you
wish to send (convey).

Let's take audio. When you speak you vibrate air molecules (generate an
acoustic wave). Those vibrations transmit out across the air (medium) and
cause another persons ear drum to vibrate in response to the acoustic wave.
The ear then converts the wave into electrical impulses in nerve cells,
again from the wave.

A man made device that does the same thing with an acoustic wave is a
microphone. (Via several different methods.) One way it does the
conversion is a conductive ribon suspended at two points vibrates with the
acoustic wave. It is surrounded by magnets and thus in a magnetic field.
When a conductor is moved in a magnetic field, a voltage is generated.
Since the movement is caused by the acoustic wave, the resultant voltage is
an electrical representation of the acoustic wave. This is baseband
information (audio) that can be used to alter a RF carrier to convey
information over a long distance.

At the receiving end, a demodulator is used to detect the information on the
radio carrier. (With AM, the device that does this is called a detector,
with FM it is called a discriminator.)







From: Richard Johnson on 22 Jan 2010 16:25

"Richard Johnson" <richj(a)bounce.this.com> wrote in message
news:hjd37s0a1s(a)news1.newsguy.com...
>
> "species8350" <not_here.5.species8350(a)xoxy.net> wrote in message
> news:a7e096ef-4c98-4b1c-b091-2c3b23d6df8e(a)p8g2000yqb.googlegroups.com...
> On Jan 18, 3:25 am, Rich Johnson <ri...(a)remove.this.tairedd.com>
> wrote:
>> On 1/8/2010 4:04 AM, species8350 wrote:
>>
>>
>>
>>
>>
>> > On Jan 7, 5:19 pm, Jeff Liebermann<je...(a)cruzio.com> wrote:
>> >> On Thu, 7 Jan 2010 03:58:50 -0800 (PST), species8350
>>
>> >> <not_here.5.species8...(a)xoxy.net> wrote:
>> >>> I know that the wifi signal is modulated.
>>
>> >> Yep.
>>
>> >>> Firstly, why does the signal need to be modulated.
>>
>> >> Because it's the modulation that carries the information (data). No
>> >> modulation, no data.
>>
>> >>> Secondly regarding g: why are ther so many coding systems used.
>>
>> >> The modulation method varies with the speed of transmission. Slow
>> >> speeds have greater range because they have a higher signal to noise
>> >> ratio for a given signal level. Higher speeds have progressively
>> >> lower signal to noise ratios for the same signal level. 802.11g will
>> >> try to negotiate and establish a modulation method that produces the
>> >> highest data rate, without having the signal to noise ratio become so
>> >> low that all that is being received are errors and garbage. More
>> >> simply, the different modulation methods trade transmission speed for
>> >> error rate. If the errors increase for some reason, the access point
>> >> will slow things down until the error rate returns to a reasonable
>> >> value.
>>
>> >> I guess you haven't looked at 802.11n, which as 77 modulation coding
>> >> schemes.
>> >> <http://www.airmagnet.com/assets/whitepaper/WP-802.11nPrimer.pdf>
>> >> The faster you go, the more complexicated the mess.
>>
>> >> --
>> >> Jeff Liebermann je...(a)cruzio.com
>> >> 150 Felker St #D http://www.LearnByDestroying.com
>> >> Santa Cruz CA 95060http://802.11junk.com
>> >> Skype: JeffLiebermann AE6KS 831-336-2558
>>
>> > Thanks for the response.
>>
>> > Is this a way of looking at modulation.
>>
>> > The data has to be transmitted, so it is converted into a wave. That
>> > wave is the modulation.
>>
>> > So, at transmission point, the wave is created. At receiver point, it
>> > is demodulated, that is, converted back into data.
>>
>> > The problem with this model is that it doesn't explain how the coding
>> > schemes will vary, depending upon data rate and errors.
>>
>> > Thanks.
>>
>> Modulation:
>>
>> Baseband information is converted into electrical information. That
>> electrical information is then used to change a "carrier" in some way to
>> convey the information.
>>
>> So, if you were using morse code, with it's dits and dahs. You could
>> simply turn the carrier on and off following the duration of the dit or
>> the dah.
>>
>> This is the first way we conveyed information. In essence, we varied
>> the amplitude of the carrier. Once we wanted to carry sound, we
>> converted it into an electrical signals and used it to directly affect
>> the amplitude of a carrier wave signal. This was called Amplitude
>> Modulation. (AM)
>>
>> Another component of a carrier wave is frequency. We could also vary it
>> in accordance with an electrically converted audio information. This is
>> called Frequency Modulation. (FM)
>>
>> Video signals, (in the USA) were impressed on to a carrier using AM.
>> (Vestigal side band AM, but still AM). Later schemes allowed the color
>> information to be modulated onto a 3.58 MHz subcarrier, using the
>> combination of phase (something a carrier also has) and AM.
>>
>> This is also how we have moved in data carriers. Using a phase of a
>> carrier and the amplitude of the carrier we can set up a scheme that
>> allows multiple bits to be conveyed with a single phase/amplitude change.
>>
>> This is modulation. Pure and simple. Once we can convey
>> information/data, we have other opportunities to set protocols for the
>> transmission of data. Here is where error correction and validation
>> come into play. In essence here we can control what a "packet" of data
>> looks like and can use math to be sure the data is valid. Also, we can
>> sequence the data with it.
>>
>> Each thing is simple, put together very powerful.- Hide quoted text -
>>
>> - Show quoted text -
>
> Thanks for responding.
>
> I have no background in the subject and am a bit confused.
>
> 'Baseband information is converted into electrical information. That
> electrical information is then used to change a "carrier" in some way
> to
> convey the information.'
>
> What is 'Baseband information'.
>
> How is it converted into electrical information?
>
> How does the electrical information change a carrier. I assume that a
> carrier is just another signal. Since the electrical information is a
> signal in itself, why not just send that?
>
> Excuse my ignorance, but if I don't ask, I 'll never learn.
>
> Best wishes
>
> S
>
> Baseband information is the electrical representation of the information
> you wish to send (convey).
>
> Let's take audio. When you speak you vibrate air molecules (generate an
> acoustic wave). Those vibrations transmit out across the air (medium) and
> cause another persons ear drum to vibrate in response to the acoustic
> wave. The ear then converts the wave into electrical impulses in nerve
> cells, again from the wave.
>
> A man made device that does the same thing with an acoustic wave is a
> microphone. (Via several different methods.) One way it does the
> conversion is a conductive ribon suspended at two points vibrates with the
> acoustic wave. It is surrounded by magnets and thus in a magnetic field.
> When a conductor is moved in a magnetic field, a voltage is generated.
> Since the movement is caused by the acoustic wave, the resultant voltage
> is an electrical representation of the acoustic wave. This is baseband
> information (audio) that can be used to alter a RF carrier to convey
> information over a long distance.
>
> At the receiving end, a demodulator is used to detect the information on
> the radio carrier. (With AM, the device that does this is called a
> detector, with FM it is called a discriminator.)
>
>
By the way, if you are interested in this, I suggest you take a few
electronics classes. DC and AC theory, then RF theory. These are basic to
understanding the technology you are using.



From: Rich Johnson on 23 Jan 2010 00:23
On 1/19/2010 3:30 AM, species8350 wrote:
> On Jan 18, 3:25 am, Rich Johnson<ri...(a)remove.this.tairedd.com>
> wrote:
>> On 1/8/2010 4:04 AM, species8350 wrote:
>>
>>
>>
>>
>>
>>> On Jan 7, 5:19 pm, Jeff Liebermann<je...(a)cruzio.com> wrote:
>>>> On Thu, 7 Jan 2010 03:58:50 -0800 (PST), species8350
>>
>>>> <not_here.5.species8...(a)xoxy.net> wrote:
>>>>> I know that the wifi signal is modulated.
>>
>>>> Yep.
>>
>>>>> Firstly, why does the signal need to be modulated.
>>
>>>> Because it's the modulation that carries the information (data). No
>>>> modulation, no data.
>>
>>>>> Secondly regarding g: why are ther so many coding systems used.
>>
>>>> The modulation method varies with the speed of transmission. Slow
>>>> speeds have greater range because they have a higher signal to noise
>>>> ratio for a given signal level. Higher speeds have progressively
>>>> lower signal to noise ratios for the same signal level. 802.11g will
>>>> try to negotiate and establish a modulation method that produces the
>>>> highest data rate, without having the signal to noise ratio become so
>>>> low that all that is being received are errors and garbage. More
>>>> simply, the different modulation methods trade transmission speed for
>>>> error rate. If the errors increase for some reason, the access point
>>>> will slow things down until the error rate returns to a reasonable
>>>> value.
>>
>>>> I guess you haven't looked at 802.11n, which as 77 modulation coding
>>>> schemes.
>>>> <http://www.airmagnet.com/assets/whitepaper/WP-802.11nPrimer.pdf>
>>>> The faster you go, the more complexicated the mess.
>>
>>>> --
>>>> Jeff Liebermann je...(a)cruzio.com
>>>> 150 Felker St #D http://www.LearnByDestroying.com
>>>> Santa Cruz CA 95060http://802.11junk.com
>>>> Skype: JeffLiebermann AE6KS 831-336-2558
>>
>>> Thanks for the response.
>>
>>> Is this a way of looking at modulation.
>>
>>> The data has to be transmitted, so it is converted into a wave. That
>>> wave is the modulation.
>>
>>> So, at transmission point, the wave is created. At receiver point, it
>>> is demodulated, that is, converted back into data.
>>
>>> The problem with this model is that it doesn't explain how the coding
>>> schemes will vary, depending upon data rate and errors.
>>
>>> Thanks.
>>
>> Modulation:
>>
>> Baseband information is converted into electrical information. That
>> electrical information is then used to change a "carrier" in some way to
>> convey the information.
>>
>> So, if you were using morse code, with it's dits and dahs. You could
>> simply turn the carrier on and off following the duration of the dit or
>> the dah.
>>
>> This is the first way we conveyed information. In essence, we varied
>> the amplitude of the carrier. Once we wanted to carry sound, we
>> converted it into an electrical signals and used it to directly affect
>> the amplitude of a carrier wave signal. This was called Amplitude
>> Modulation. (AM)
>>
>> Another component of a carrier wave is frequency. We could also vary it
>> in accordance with an electrically converted audio information. This is
>> called Frequency Modulation. (FM)
>>
>> Video signals, (in the USA) were impressed on to a carrier using AM.
>> (Vestigal side band AM, but still AM). Later schemes allowed the color
>> information to be modulated onto a 3.58 MHz subcarrier, using the
>> combination of phase (something a carrier also has) and AM.
>>
>> This is also how we have moved in data carriers. Using a phase of a
>> carrier and the amplitude of the carrier we can set up a scheme that
>> allows multiple bits to be conveyed with a single phase/amplitude change.
>>
>> This is modulation. Pure and simple. Once we can convey
>> information/data, we have other opportunities to set protocols for the
>> transmission of data. Here is where error correction and validation
>> come into play. In essence here we can control what a "packet" of data
>> looks like and can use math to be sure the data is valid. Also, we can
>> sequence the data with it.
>>
>> Each thing is simple, put together very powerful.- Hide quoted text -
>>
>> - Show quoted text -
>
> Thanks for responding.
>
> I have no background in the subject and am a bit confused.
>
> 'Baseband information is converted into electrical information. That
> electrical information is then used to change a "carrier" in some way
> to
> convey the information.'
>
> What is 'Baseband information'.
>
> How is it converted into electrical information?
>
> How does the electrical information change a carrier. I assume that a
> carrier is just another signal. Since the electrical information is a
> signal in itself, why not just send that?
>
> Excuse my ignorance, but if I don't ask, I 'll never learn.
>
> Best wishes
>
> S
>
>
Oops, I did not answer all of your questions. Now that you know what
base band signal is, you ask why don't we send it directly. We can do
that through a wire and as long as there are no other signals using the
same frequencies, we are OK.

Baseband audio is from 20 Hz through 20KHz. If you had another signal
there, it would be like being in a room full of very loud people and
trying to carry a conversation on with another person 100 ft away in the
same room. Not a good way to do that.

However if in the room, we have everyone take turns, you can possibly
talk to someone across the room, but would have to wait turns, and the
conversation would take a very long time.

Here we have the need to carry all the conversations at once. Well, we
have the ability to put the baseband information on to a much higher
frequency and send it. Keep every conversation to their own frequency
and now everyone can talk at the same time, as long the two involved in
the specific conversation are on the same frequency. (This is called
frequency division multiplexing in RF, and wave division multiplexing in
fiber optic communications.)

If you listen to radio, or TV, you do this. Tune to the channel
(frequency) you want to hear, and volia!

There is another type of multiplexing, called time division
multiplexing. An example of that was the conversation room where we all
took turns talking. You can do both time and frequency division
multiplexing. Think of it as watching your favorite program on a TV
channel, then when it is over, someone else's program comes on for the
next half hour.


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