Modulation methods

Sirs,

Let me first say that probably this is a very basic question.

In case of modulating carrier signals with data and doing de-modulation at
the receiver, what would be the disadvantage if data is simply added to the
carrier frequency and then performing filtering at the receiver to remove
the carrier signal and recover the data.

Thanks, manish

On Tuesday, June 11, 2013 4:18:56 AM UTC-4, manishp wrote:
> Sirs,
> 
> 
> 
> Let me first say that probably this is a very basic question.
> 
> 
> 
> In case of modulating carrier signals with data and doing de-modulation at
> 
> the receiver, what would be the disadvantage if data is simply added to the
> 
> carrier frequency and then performing filtering at the receiver to remove
> 
> the carrier signal and recover the data.
> 
> 
> 
> Thanks, manish

What does "data is simply added to the carrier frequency" mean?
Could you possibly add just a **little** explanation to this
statement to describe what you mean by adding data to carrier
frequency? 

I will construct a multiple-choice question to make your task
as simple as possible.  Suppose your data is d(t) and your carrier
signal is cos(wt). What is the result of "adding" data to the
carrier frequency?

A.  d(t)+cos(wt)
B.  cos((w+d(t))t)
C.  d(t)cos(wt)
D.  cos(wt+d(t))
E.  All of the above
F.  None of the above

Hint: the answer to a multiple-choice question is not Yes.

Dilip Sarwate

>On Tuesday, June 11, 2013 4:18:56 AM UTC-4, manishp wrote:
>> Sirs,
>> 
>> 
>> 
>> Let me first say that probably this is a very basic question.
>> 
>> 
>> 
>> In case of modulating carrier signals with data and doing de-modulation
at
>> 
>> the receiver, what would be the disadvantage if data is simply added to
the
>> 
>> carrier frequency and then performing filtering at the receiver to
remove
>> 
>> the carrier signal and recover the data.
>> 
>> 
>> 
>> Thanks, manish
>
>What does "data is simply added to the carrier frequency" mean?
>Could you possibly add just a **little** explanation to this
>statement to describe what you mean by adding data to carrier
>frequency? 
>
>I will construct a multiple-choice question to make your task
>as simple as possible.  Suppose your data is d(t) and your carrier
>signal is cos(wt). What is the result of "adding" data to the
>carrier frequency?
>
>A.  d(t)+cos(wt)
>B.  cos((w+d(t))t)
>C.  d(t)cos(wt)
>D.  cos(wt+d(t))
>E.  All of the above
>F.  None of the above
>
>Hint: the answer to a multiple-choice question is not Yes.
>
>Dilip Sarwate
>

I wish there was a 'Like' button somewhere here.

On Tue, 11 Jun 2013 03:18:56 -0500, "manishp" <58525@dsprelated>
wrote:

>Sirs,
>
>Let me first say that probably this is a very basic question.
>
>In case of modulating carrier signals with data and doing de-modulation at
>the receiver, what would be the disadvantage if data is simply added to the
>carrier frequency and then performing filtering at the receiver to remove
>the carrier signal and recover the data.
>
>Thanks, manish

You need to answer Dilip's question, but you also need to say what you
mean by "filtering at the receiver to remove the carrier signal and
recover the data".   Usually you don't need to "filter" away the
carrier unless the signal is not "suppressed carrier", which is
actually fairly rare these days.

I think you might be asking about using rectangular (i.e., unfiltered)
pulses at the transmitter and doing all the filtering in the receiver,
but I could easily be wrong about that.


Eric Jacobsen
Anchor Hill Communications
http://www.anchorhill.com

>> Let me first say that probably this is a very basic question.
>> In case of modulating carrier signals with data and doing de-modulation
at
>> the receiver, what would be the disadvantage if data is simply added to
the
 
>> carrier frequency and then performing filtering at the receiver to
remove
>> the carrier signal and recover the data.
 
>> Thanks, manish
>
>What does "data is simply added to the carrier frequency" mean?
>Could you possibly add just a **little** explanation to this
>statement to describe what you mean by adding data to carrier
>frequency? 
>
>I will construct a multiple-choice question to make your task
>as simple as possible.  Suppose your data is d(t) and your carrier
>signal is cos(wt). What is the result of "adding" data to the
>carrier frequency?
>
>A.  d(t)+cos(wt)
>B.  cos((w+d(t))t)
>C.  d(t)cos(wt)
>D.  cos(wt+d(t))
>E.  All of the above
>F.  None of the above
>
>Hint: the answer to a multiple-choice question is not Yes.

Sir, thanks for the response (I will ignore the sarcasm part and continue)
...

Anyway, 

B - no ... not FM
C - no ... not AM
D - no ... not PM
A - yes ... simply add carrier with d(t) like a noise would get added.
Since the frequencies of carrier and baseband signals are known, it would
be possible to filter out the carrier signal and get the baseband signal.

Again, I am interested to know if this is possible purely from theoretical
perspective. And if yes, what are its demerits ...

thanks, manish ...

>>> Let me first say that probably this is a very basic question.
>>> In case of modulating carrier signals with data and doing
de-modulation
>at
>>> the receiver, what would be the disadvantage if data is simply added
to
>the
> 
>>> carrier frequency and then performing filtering at the receiver to
>remove
>>> the carrier signal and recover the data.
> 
>>> Thanks, manish
>>
>>What does "data is simply added to the carrier frequency" mean?
>>Could you possibly add just a **little** explanation to this
>>statement to describe what you mean by adding data to carrier
>>frequency? 
>>
>>I will construct a multiple-choice question to make your task
>>as simple as possible.  Suppose your data is d(t) and your carrier
>>signal is cos(wt). What is the result of "adding" data to the
>>carrier frequency?
>>
>>A.  d(t)+cos(wt)
>>B.  cos((w+d(t))t)
>>C.  d(t)cos(wt)
>>D.  cos(wt+d(t))
>>E.  All of the above
>>F.  None of the above
>>
>>Hint: the answer to a multiple-choice question is not Yes.
>
>Sir, thanks for the response (I will ignore the sarcasm part and
continue)
>...
>
>Anyway, 
>
>B - no ... not FM
>C - no ... not AM
>D - no ... not PM
>A - yes ... simply add carrier with d(t) like a noise would get added.
>Since the frequencies of carrier and baseband signals are known, it would
>be possible to filter out the carrier signal and get the baseband signal.
>
>Again, I am interested to know if this is possible purely from
theoretical
>perspective. And if yes, what are its demerits ...
>
>thanks, manish ...
>

I'm certain no offense was intended, its just kind of an odd premise.

Think of it this way, in the case you have:

    x(t) = d(t) + c(t)

where x(t) is the transmitted signal, d(t) is the data and c(t) is the
carrier.

This would not constitute modulation as none of the properties of the
carrier signal are changing with time.  This is fine in the same sense that
transmitting the data without any carrier would be fine.  In fact you may
as well omit the carrier all together, since it isn't providing any
utility.

If you want to think about the limitations of this scheme, imagine radio
stations transmitting audio data.

    x(t) = x1(t) + x2(t) = d1(t) + d2(t) + c1(t) + c2(t)

Filtering out the carriers to obtain the recieved signal:

    y(t) = d1(t) + d2(t)

If d1 and d2 are audio, they would overlap and you would have to figure out
how to seperate them.  It's not impossible, but how would you do it?  Using
modulation puts signals into different parts of the spectrum, allowing them
to be transmitted simultaneously on the same medium and separetly
reconstructed.

On 12.6.13 11:25 , manishp wrote:
>>> Let me first say that probably this is a very basic question.
>>> In case of modulating carrier signals with data and doing de-modulation
> at
>>> the receiver, what would be the disadvantage if data is simply added to
> the
>
>>> carrier frequency and then performing filtering at the receiver to
> remove
>>> the carrier signal and recover the data.
>
>>> Thanks, manish
>>
>> What does "data is simply added to the carrier frequency" mean?
>> Could you possibly add just a **little** explanation to this
>> statement to describe what you mean by adding data to carrier
>> frequency?
>>
>> I will construct a multiple-choice question to make your task
>> as simple as possible.  Suppose your data is d(t) and your carrier
>> signal is cos(wt). What is the result of "adding" data to the
>> carrier frequency?
>>
>> A.  d(t)+cos(wt)
>> B.  cos((w+d(t))t)
>> C.  d(t)cos(wt)
>> D.  cos(wt+d(t))
>> E.  All of the above
>> F.  None of the above
>>
>> Hint: the answer to a multiple-choice question is not Yes.
>
> Sir, thanks for the response (I will ignore the sarcasm part and continue)
> ...
>
> Anyway,
>
> B - no ... not FM
> C - no ... not AM
> D - no ... not PM
> A - yes ... simply add carrier with d(t) like a noise would get added.
> Since the frequencies of carrier and baseband signals are known, it would
> be possible to filter out the carrier signal and get the baseband signal.
>
> Again, I am interested to know if this is possible purely from theoretical
> perspective. And if yes, what are its demerits ...
>
> thanks, manish ...


Yes, you can, but you do not win anything of the carrier.
You could as well transfer the signal and carrier in separate
cables and note that the carrier cable and the whole carrier
are unnecessary.

The addition does not transfer any of the signal frequency
components to the vicinity of the carrier, as long as the
processing chain is linear.

-- 

Tauno Voipio

>>>> Let me first say that probably this is a very basic question.
>>>> In case of modulating carrier signals with data and doing
>de-modulation
>>at
>>>> the receiver, what would be the disadvantage if data is simply added
>to
>>the
>> 
>>>> carrier frequency and then performing filtering at the receiver to
>>remove
>>>> the carrier signal and recover the data.
>> 
>>>> Thanks, manish
>>>
>>>What does "data is simply added to the carrier frequency" mean?
>>>Could you possibly add just a **little** explanation to this
>>>statement to describe what you mean by adding data to carrier
>>>frequency? 
>>>
>>>I will construct a multiple-choice question to make your task
>>>as simple as possible.  Suppose your data is d(t) and your carrier
>>>signal is cos(wt). What is the result of "adding" data to the
>>>carrier frequency?
>>>
>>>A.  d(t)+cos(wt)
>>>B.  cos((w+d(t))t)
>>>C.  d(t)cos(wt)
>>>D.  cos(wt+d(t))
>>>E.  All of the above
>>>F.  None of the above
>>>
>>>Hint: the answer to a multiple-choice question is not Yes.
>>
>>Sir, thanks for the response (I will ignore the sarcasm part and
>continue)
>>...
>>
>>Anyway, 
>>
>>B - no ... not FM
>>C - no ... not AM
>>D - no ... not PM
>>A - yes ... simply add carrier with d(t) like a noise would get added.
>>Since the frequencies of carrier and baseband signals are known, it
would
>>be possible to filter out the carrier signal and get the baseband
signal.
>>
>>Again, I am interested to know if this is possible purely from
>theoretical
>>perspective. And if yes, what are its demerits ...
>>
>>thanks, manish ...
>>
>
>I'm certain no offense was intended, its just kind of an odd premise.
>
>Think of it this way, in the case you have:
>
>    x(t) = d(t) + c(t)
>
>where x(t) is the transmitted signal, d(t) is the data and c(t) is the
>carrier.
>
>This would not constitute modulation as none of the properties of the
>carrier signal are changing with time.  This is fine in the same sense
that
>transmitting the data without any carrier would be fine.  In fact you may
>as well omit the carrier all together, since it isn't providing any
>utility.
>
>If you want to think about the limitations of this scheme, imagine radio
>stations transmitting audio data.
>
>    x(t) = x1(t) + x2(t) = d1(t) + d2(t) + c1(t) + c2(t)
>
>Filtering out the carriers to obtain the recieved signal:
>
>    y(t) = d1(t) + d2(t)
>
>If d1 and d2 are audio, they would overlap and you would have to figure
out
>how to seperate them.  It's not impossible, but how would you do it? 
Using
>modulation puts signals into different parts of the spectrum, allowing
them
>to be transmitted simultaneously on the same medium and separetly
>reconstructed.
>
Thanks a lot ... makes sense to me ...
Thanks all

On Wed, 12 Jun 2013 03:25:35 -0500, manishp wrote:

>>> Let me first say that probably this is a very basic question.
>>> In case of modulating carrier signals with data and doing
>>> de-modulation
> at
>>> the receiver, what would be the disadvantage if data is simply added
>>> to
> the
>  
>>> carrier frequency and then performing filtering at the receiver to
> remove
>>> the carrier signal and recover the data.
>  
>>> Thanks, manish
>>
>>What does "data is simply added to the carrier frequency" mean? Could
>>you possibly add just a **little** explanation to this statement to
>>describe what you mean by adding data to carrier frequency?
>>
>>I will construct a multiple-choice question to make your task as simple
>>as possible.  Suppose your data is d(t) and your carrier signal is
>>cos(wt). What is the result of "adding" data to the carrier frequency?
>>
>>A.  d(t)+cos(wt)
>>B.  cos((w+d(t))t)
>>C.  d(t)cos(wt)
>>D.  cos(wt+d(t))
>>E.  All of the above F.  None of the above
>>
>>Hint: the answer to a multiple-choice question is not Yes.
> 
> Sir, thanks for the response (I will ignore the sarcasm part and
> continue)
> ..
> 
> Anyway,
> 
> B - no ... not FM C - no ... not AM D - no ... not PM A - yes ... simply
> add carrier with d(t) like a noise would get added. Since the
> frequencies of carrier and baseband signals are known, it would be
> possible to filter out the carrier signal and get the baseband signal.
> 
> Again, I am interested to know if this is possible purely from
> theoretical perspective. And if yes, what are its demerits ...
> 
> thanks, manish ...

That's not modulation.  That's just adding two signals.

Modulation of a carrier pretty much means that you are taking a signal at 
exactly one frequency (the carrier), and you are using some other signal 
(the desired signal) to vary some parameter of the carrier such that the 
desired signal is literally carried by the carrier signal through media 
that the carrier can travel through.

So, if I have an antenna and radio system that will conduct signals in 
the area of 2MHz but not close to DC, then I can modulate a 2MHz carrier 
in some manner with my low-bandwidth signal and get that low-bandwidth 
signal out.

If you're not doing that, you're not modulating

-- 
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

If the speed of light were about a million times slower, then you could just connect a microphone directly to an antenna and you would have your own radio station! Unfortunately, given that we can't change the speed of light, your antenna would need to be about 1000 miles long. Hence the need for modulation. 

The now-discontinued coastal marine navigation system (the name escapes me) used a carrier down below 100khz if I remember correctly. That's a pretty big antenna.

Bob