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graciousparul
Joined: 19 Jan 2008
Posts: 90
Helped: 2
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 09 Aug 2008 11:46 Why we need Modulation? |
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Hi,
Can any one answer why we need Modulation?
Thanks in advance 
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rkodaira
Joined: 08 Jun 2004
Posts: 332
Helped: 54
Location: Sao Paulo - Brasil
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| 09 Aug 2008 12:51 Re: Why we need Modulation? |
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It is a very open question. Goals vary depending on the kind of modulation.
For example: in broadcasting we use modulation (in frequency or amplitude) to have feasible antennas sizes (you could broadcast in audio frequency but the antennas would be giant). You basically transmit audio or video information over a higher frequency carrier. AM-SSB saves energy to transmit info. The range is improved also with modulation, indirectly less power is necessary.
For PCM (pulse code modulation) you can transmit data over a serial and digitised flow.
PWM (pulse width modulation) is used to have an on-off signal proportional to a desired average voltage to control something.
LASER can be modulated to transmit data over optical fibers, changing the way of transmission.
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Bhanumurthy
Joined: 18 Jun 2008
Posts: 201
Helped: 95
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| 09 Aug 2008 13:40 Re: Why we need Modulation? |
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Hi,
In simple terms, modulation is required to transmit signals from variuos sources simultaneously over a common channel by means of 'multiplexing'.For ex., the bandwidth of speech signals is 3.3KHz.,and transmitting N no.of speech signals simultaneously each of BW 3.3KHz causes interference.Hence,to overcome this problem, each speech signal is modulated onto one of N carriers of frequencies 60KHz,64KHz,68KHz etc...
Hope u got my answer
Regards
Bhanumurthy.
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bhatt_tanmay
Joined: 18 Sep 2006
Posts: 106
Helped: 9
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| 09 Aug 2008 14:36 Re: Why we need Modulation? |
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The aim of digital modulation is to transfer a digital bit stream over an analog bandpass channel, for example over the public switched telephone network (where a filter limits the frequency range to between 300 and 3400 Hz) or a limited radio frequency band.
The aim of analog modulation is to transfer an analog lowpass signal, for example an audio signal or TV signal, over an analog bandpass channel, for example a limited radio frequency band or a cable TV network channel.
Analog and digital modulation facilitate frequency division multiplexing (FDM), where several low pass information signals are transferred simultaneously over the same shared physical medium, using separate bandpass channels.
The aim of digital baseband modulation methods, also known as line coding, is to transfer a digital bit stream over a lowpass channel, typically a non-filtered copper wire such as a serial bus or a wired local area network.
The aim of pulse modulation methods is to transfer a narrowband analog signal, for example a phone call over a wideband lowpass channel or, in some of the schemes, as a bit stream over another digital transmission system.
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subharpe
Joined: 09 Jan 2008
Posts: 163
Helped: 21
Location: Bangalore,India
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| 11 Aug 2008 12:20 Re: Why we need Modulation? |
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Hi,
The fundamental need of modulation taught in any electronic communication course is like this: For transmitting and receiving a signal of wavelength λ the antenna aperture size should be of the order of atleast λ/10. For sending awave which is 5kHz, say the antenna size you can calculate, given the speed of the em wave is c. The antenna size you ill find is not practicable. Therefore modulation is done to modulate a very high frequency (low λ) signal with the actual signal so that a feasible antenna can be made and operated for communication.
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Awarapunshee
Joined: 11 Jul 2007
Posts: 338
Helped: 45
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| 11 Aug 2008 12:40 Re: Why we need Modulation? |
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| graciousparul wrote: |
Hi,
Can any one answer why we need Modulation?
Thanks in advance |
Your question is very general. or broad...
AM FM etc then, we need to send the information, else are explained above.
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xulfee
Joined: 27 May 2008
Posts: 230
Helped: 25
Location: Pakistan
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| 12 Aug 2008 6:04 Why we need Modulation? |
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| modulation is needed to send signal through the long path,the communication which doesn't require modulation is baseband communication n that need modulation is broadband communication,
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RF-OM
Joined: 03 Aug 2007
Posts: 607
Helped: 113
Location: The Earth
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| 12 Aug 2008 6:42 Re: Why we need Modulation? |
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| Let's take it as easy as it possible. For radio communications you need to have a carrier. Let's say it is the Camel. Then you need to transport some stuff on this Camel. How can you do it? Right, you need a bag to put all your small things inside. So modulation is this bag on Camel's back which serve as the tool to transfer the information (think about it as your small things) on the major transportation means (Camel). By the way, there are actually two bags on each side of the Camel (carrier), one bag is the Low Side Band and another is the Upper Side Band (LSB and USB). Now you need a bit more stuff like food for the Camel. I think you may find the electronic analog for this stuff too.
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manikandan_5025
Joined: 11 Aug 2008
Posts: 13
Helped: 1
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| 12 Aug 2008 6:48 Re: Why we need Modulation? |
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| to modulate the weak signal to strong
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hkBattousai
Joined: 16 Jun 2007
Posts: 86
Helped: 4
Location: Turkey
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| 12 Aug 2008 17:13 Why we need Modulation? |
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There are 3 major reasons :
1) To use much more smaller antennas.
2) Channel allocation for todays thousands of todays users.
3) For better noise immunity. (This one is a rather smaller reason)
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SWINI
Joined: 19 Mar 2007
Posts: 48
Helped: 2
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| 18 Aug 2008 10:51 Why we need Modulation? |
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the main use of modulatoion is to reduce the length of antennas..
previously cars use to use inductors along with the antenna to reduce the length.. but now-a-days use of modulation lessen the work..
basic aim of modulation in vague terms may b to increase the signal strength
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ckshivaram
Joined: 21 Apr 2008
Posts: 327
Helped: 22
Location: india
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| 20 Aug 2008 2:52 Re: Why we need Modulation? |
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Can any one answer why we need Modulation?
It is a simple logic,
why do we pack an item or bunch of papers before we courier it. what happens if we try to just send it with out packing.
In short distance u can take care of the item and deliver it properly, but in long distance if u send it without packing, there are chances that some papers may loose in the transit, or some unwanted papers may be mixed by somebody.That will result in lose of information and waste of time and money.
In the same way when u want to transmit a signal in free air, imagine there are so many obstructions like trees, buildings,etc, your signal or information will be lost or may be affected by noise and if it reaches the the destination then you wont be able to make out what the original message was.
In order to transmit the signal properly over a long distance modulation is required. There are different methods of modulation, and it depends on the requirement.
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saruman1983
Joined: 12 Oct 2005
Posts: 25
Helped: 4
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| 21 Aug 2008 12:01 Re: Why we need Modulation? |
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Well, an additional question
Does attenuation in the air differ from frequency to frequency? i.e. is attenuation frequency dependent so that trancieving in higher frequencies is more effective in terms of the received signal level?
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hkBattousai
Joined: 16 Jun 2007
Posts: 86
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Location: Turkey
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| 21 Aug 2008 12:07 Why we need Modulation? |
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Of course it differs. The frequency response of 'air' is mostly linear and not constant. Under some conditions it can even be non linear. Or its frequency respons may not be simply decreasing or increasing by freqeuncy; it can have negative or positive peaks at some frequencies.
In the worst case, we divide the channel (and the message) into small intervals in the frequency domain such that each interval behaves approximtely constant. And send each message piece in a different interval.
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RF-OM
Joined: 03 Aug 2007
Posts: 607
Helped: 113
Location: The Earth
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| 21 Aug 2008 20:30 Re: Why we need Modulation? |
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To ckshivaram,
Modulation was invented not for packing and actually does not related to it. Modulation is the process to put information on the carrier in order to be able to send it through the air or any other applicable media. Modulation can be used for packing the data, but it is not packing itself.
Added after 5 minutes:
To SWINI,
I like your joke.
Just be sure that the author of the question understood it as the joke.
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te04-0202
Joined: 17 Jun 2008
Posts: 17
Helped: 1
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| 22 Aug 2008 20:30 Re: Why we need Modulation? |
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| Modulation is used to encrypt data, to send signals over large distances with minimum noise.
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