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| Analog and Digital Communication |
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| The concept of information is central to communication. There is no precise definition of the word "information". So, instead of information, we deal with "message". |
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| Message is defined as the physical manifestation of information as produced by the source |
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| There are two distinct message categories: |
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| An analog message is a physical quantity that varies with time usually in a smooth and continuous fashion. |
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| Examples of analog messages are: |
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| (i) the acoustic pressure produced when you speak |
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| (ii) the angular position of an aircraft gyro |
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| (iii) the light intensity at some point in a television image. |
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| A digital message is an ordered sequence of symbols selected from a finite set of discrete elements. |
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| Examples of digital messages are: |
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| (i) letters printed on this page |
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| (ii) listing of hourly temperature readings |
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| (iii) the keys you press at a computer terminal. |
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| Whether the message is analog or digital, it needs to be converted into an electrical signal. (There are only few messages, which are inherently electrical.) |
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