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    need for modulation

    Hi!

    why we need modulation before transmiting signal in to space or line?

    Yours sincerely,

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    need of modulation

    mainly to decrease the antenna size + simultaneously send data + to multiplex data+ (lower loss +lower dispersion in EMW)


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    •   Alt23rd January 2007, 04:14

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    why modulation is needed

    Hi Dear RatanaRETH!

    You know, to transmit data through any channels you have to adopt the data style with them e.g. to have a link over the sea you should use low frequencies due to loss caused by water. Aside this the antenna needed to send and recieve data would have a length proportional to wavelength i.e. higher frequency needs shorter antenna and vice versa. Finally to utilize a channel properarly you shouldn't use it only for one link and it's better to apply more links in one channel.

    Well to do all of these you have to change the frequency of your signal which is not a good way due to distortion, etc, and as you know the signals are a band of frequency in frequency domain. So you may use modulation in order to change the frequency of a signal without destroying the original signal. Through modulation you may change another signal amplitude, phase and frequency according to information signal.

    Thanks!


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    why do we need to do modulation

    Modulation is needed for following reasons..

    1) To send a signal over long distance it requires more energy. Energy and frequency are related by the following planck's formula

    E = hv;

    E = Energy of the signal
    h = plancks constant
    v = frequency of the signal

    So when the frequency is low , energy will be obviously low. To increase the energy of the signal we need to increase the frequency. This is achieved by modulation.
    Modulation is the process of increasing the frequency content of a signal ( indirectly increasing the energy of the signal to enable it to travel long distance). Demodulation is the exactly opposite process to it ( Decreasing the frequency content of the signal)

    2) to decrease antenna height. For transmitting a signal of wavelength
    λ the antenna height must be λ/4. So if we want to send a 1 Hz (λ=3*10^8 m) signal ( very very low frequency) using an antenna , its height must be 75,000 Km ( impossible to build such a huge antenna ). If the same signal is modulated to some high frequency say 88 MHZ ( λ = 3.4 m ) , antenna height needed is 0.8522 m (quite easy to construct !!! ) (88 MHZ is the starting range of Frequency modulation which exists upto 108 MHZ).


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    why we use modulation

    Dear safwatonline and Everybody,

    Hello! Could you detail me from your answer in simultaneously send data + to multiplex data please? Moreover For everyone,what are advantage and disadvantage when I don't use Modulation before transmite signal on transmission line?

    Your faithfully,



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    why need modulation

    Hi Dear RatanaRETH!

    You asked about simultaneously transmittion data. I give you an example. You know there are many Radio channels they want to broadcast over an area, so what they can do to obtain this! Simply they must arrange their channels so that no channel disturbs another one. By using modulation they can do it. I mean every channel changes its own frequencies.

    If you don't use modulation before transmittion e.g. in a case of 'Speech Signal', you have to use an antenna as long as 75000 meters! Because usually antenna legths are a quarter of wavelength. Of course if you are not using an antenna or only one data stream exists, you don't have to use modulation. e.g. an output to a speaker doen't need modulation because you apply a wire as the channel and only one data is Transmitted.

    However when you modulate any signal you must demodulate it to obtain the original signal. And sometimes the process of demodulation is more difficult than modulation.

    Thanks!


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    why do we need to do modulation?

    To transmit you need at least a carrier signal. It is continious wave with constant amplitude and frequency. On receive site you will be able to indicate only if carrier is present or not and nothing more. If you allso want to transmit any data, information or audio signal, for example, you must modulate this carrier signal. Process is caled modulation and it can be of different type or kind from simple AM, FM, SSB to QPSK and other digital types.



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    what is need of modulation

    simultaineous transmission: consider u transmit speech signal without modulation then this signal will interfer with the normal voice in the air (from poeple and radios and everything) thats why u get radio station at different frequencies.

    multiplexing signals: the same concept as simultanious transmission but from the sender prespective , say u need DSL on ur landline then u need to mudulate the DSL data on a higher carrier to prevent interfering with telephone signal.


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    why do we need to modulate

    Hello!

    Thank U to all of you! If I have one way line to transmite signal in long distance, should I need modulation or not. Why?

    The perfect smile in ur life!



    •   Alt25th January 2007, 04:36

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    why modulation is needed?

    well , it deppends on attenuation , in fiber optics u don't modulate but u send a baseband signa cause the BW is huge, i.e u can time division multiplex , and since u have ur line then u don't worry about interference , also the loss in fiber is much lower than copper , so u don't modulate.



    •   Alt25th January 2007, 06:40

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    why is modulation needed

    The question can not be answered.



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    what is the need for modulation?

    by doing modulation we can cover large distance communication

    and we can do multiplexing of more signals on same transmission line by providing different carrier signals


    the main and important advantage is tht we can reduce anttena size buy using following formula

    antenna hight is expressed in terms of quater wavelengh... for 1 khz signal we need more antena hight but if you do modualtion for this signal by adding HF carrier signal then u need small length of anteena .



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    why do we need modulation

    Hello safwatonline!

    Is Attenuation relevant to use modulation or not?

    The perfect smile in ur life!



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    Re: Why we need modulation?

    I'm going to revive this post for a hypothetical question.

    Suppose we CAN build an antenna that is 75km long. What else would require us to modulate speech signals?

    So we'd have some type of transmitter, transmitting a direct speech signal at say 1kW.

    Would that be a 1kW audible signal heard over the air? (My guess is no because it's electromagnetic and not instantiating pressure in the air to make sound waves?)

    According to the Friis equation, a higher wavelength has less path-loss (it's in the numerator). Does this mean that you would need less equivalent antenna gain on that 75km-long antenna to transmit the same distance as say an FM-radio signal?

    Silly hypothetical question, but it got my brain thinking about some of the fundamental physics ...



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    Re: Why we need modulation?

    Ummmmm Do you actually know how a radio transmitter works ?

    Quote Originally Posted by tzoom84 View Post
    I'm going to revive this post for a hypothetical question.
    Suppose we CAN build an antenna that is 75km long. What else would require us to modulate speech signals?
    Speech signals ARE the modulation

    So we'd have some type of transmitter, transmitting a direct speech signal at say 1kW.
    Well that is done with a hearing loop system for people with hearing aids.... Ausio from a microphone or other source goes into a standard audio amplifier of which the output is into a large loop around the room. The hearing aids inductively pick up the signal radiated from the loop.

    Would that be a 1kW audible signal heard over the air? (My guess is no because it's electromagnetic and not instantiating pressure in the air to make sound waves?)
    thats right see previous comment its inductive

    According to the Friis equation, a higher wavelength has less path-loss (it's in the numerator). Does this mean that you would need less equivalent antenna gain on that 75km-long antenna to transmit the same distance as say an FM-radio signal?
    HUH ???? higher wavelength ??? no such thing ... do you mean higher frequency (shorter wavelength) ?
    the higher the freq, the higher the pathloss

    Silly hypothetical question, but it got my brain thinking about some of the fundamental physics ...
    time for you to read some basic books on radio transmitters, modulation, freq and wavelength I think :)
    start with the ARRL Handbook

    cheers
    Dave



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    Re: Why we need modulation?

    Thank you for the response. Your example of the hearing loop system was perfect.

    Although I think there was some confusion in the way I phrased my questions. Some responses:

    1) in response to "Speech signals ARE the modulation":

    Yes, technically speech is modulation. But most RF context considers modulation as a means of conveying a baseband information signal, such as analog speech, over a carrier signal. Or in wikipedia's page on modulation as an example: "In telecommunications, modulation is the process of conveying a message signal, for example a digital bit stream or an analog audio signal, inside another signal that can be physically transmitted. "

    Perhaps I should have phrased the question as "What else would require us to wirelessly transmit a baseband speech signal directly without FURTHER modulation onto a carrier signal?".

    2) In response to "HUH ??? higher wavelength ??? ...":

    Yes, wrong term perhaps. I used "Higher" as "of larger magnitude". So higher = larger = bigger = longer ... whatever. Given that, my statement is perfectly correct w.r.t. the Friis equation.

    3) In response to "Ummmmm Do you actually know how a radio transmitter works" + "time for you to read some basic books on radio transmitters":

    Actually I think it was more just miscommunication with regard to terminology than anything else. Why the hostile tone and unnecessary negative comments? I do appreciate that you provided a technical response though. I've certainly learned to respect the comments of professors throughout my education ... even the arrogant ones.

    4) Other:

    I'm still curious on the some of the key differences in design between a baseband transmitter and one say for an AM broadcast (amplifier parameters, any other components needed aside from a mixer/oscillator).
    But don't fret and no need for more bashing, I'll just go "read a book"


    Thanks for being so "welcoming", take care.



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    Re: Why we need modulation?

    Sorry if I sounded hostile
    but a lot of your questions comments were worded as tho written by some one with very mixed up ideas and really didnt have any idea of what it was all about and needed to do some reading to understand basic radio principles

    I guess part of my frustration lay in reading some of the totally wild and stupid comments written much earlier when the topic was originally active ... months ago sorry for taking some of that out on you :(

    .... dave takes a chill pill ;)





    Quote Originally Posted by tzoom84 View Post
    Thank you for the response. Your example of the hearing loop system was perfect.

    Although I think there was some confusion in the way I phrased my questions. Some responses:

    1) in response to "Speech signals ARE the modulation":

    Yes, technically speech is modulation. But most RF context considers modulation as a means of conveying a baseband information signal, such as analog speech, over a carrier signal. Or in wikipedia's page on modulation as an example: "In telecommunications, modulation is the process of conveying a message signal, for example a digital bit stream or an analog audio signal, inside another signal that can be physically transmitted. "

    Perhaps I should have phrased the question as "What else would require us to wirelessly transmit a baseband speech signal directly without FURTHER modulation onto a carrier signal?".

    2) In response to "HUH ??? higher wavelength ??? ...":

    Yes, wrong term perhaps. I used "Higher" as "of larger magnitude". So higher = larger = bigger = longer ... whatever. Given that, my statement is perfectly correct w.r.t. the Friis equation.

    3) In response to "Ummmmm Do you actually know how a radio transmitter works" + "time for you to read some basic books on radio transmitters":

    Actually I think it was more just miscommunication with regard to terminology than anything else. Why the hostile tone and unnecessary negative comments? I do appreciate that you provided a technical response though. I've certainly learned to respect the comments of professors throughout my education ... even the arrogant ones.

    4) Other:

    I'm still curious on the some of the key differences in design between a baseband transmitter and one say for an AM broadcast (amplifier parameters, any other components needed aside from a mixer/oscillator).
    But don't fret and no need for more bashing, I'll just go "read a book"


    Thanks for being so "welcoming", take care.



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    Re: Why we need modulation?

    In order to efficiently emit a 1 kHz signal in space you need an antenna ~ 300 km long which is practically impossible to be built!

    In order to efficiently emit a 1 GHz signal in space you need an antenna just ~ 30 cm long!

    This is the main reason you need modulation! Without modulation, wireless low frequency transmissions (ex. voice transmissions) would be impossible.

    The optimum length of an antenna is calculated using Maxwell Equations.
    Last edited by tempos; 8th January 2011 at 03:21.



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    Re: Why we need modulation?

    Modulation is needed becuase of 3 reasons.

    1.Low frequency signals are more immune to noise. So the
    low frequency information signal should be mix up with high
    frequency carrier to reduce noise affection

    2.All sounds are with in the range from 20 Hz to 20 kHz. If
    we send audio signal directly all signals from different
    sources would be inseperably mixup.So it is necessary to
    convert the information signal to different portions of the
    electromagnetic spectrum

    3.For efficient transmission and reception of Electro-
    maganenic waves the Transmitting and Receiving antennas
    should have lenths comparable to a quarter-wavelength of
    the frequency used. This is 75 meters (75 m) at 1 magahertz
    (1 MHz), but at 15 kHz it has incrased to 5000 m (5 Kilo
    meter). A vertical antenna of this size is impracticable.

    Because of above reasons modulation is needed for
    transmitting Electro-magnetic Waves.



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    Re: Why we need modulation?

    thank you, I really like this information.
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