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Analog signal basics

  1. Dec 15, 2012 #1
    is it true that analog signals are the logarithmic version of the natural signals... and hence the name a-na -log.?

    what is the meaning of infinite information contained in analog or continous valued signal?

    please elaborate
  2. jcsd
  3. Dec 15, 2012 #2


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    ankities, Welcome to Physics Forums!

    The term “analog” in general is described here:

    The term when used in electronics is described here:

    If, after reading at these sites you still have some doubts or questions, come right back here and post them. Members here are always ready an willing to assist any true searcher advance her scientific knowledge.

  4. Dec 15, 2012 #3


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    An analogue is a word that is used for something that 'corresponds' to something else. I guess the root is the same as in the word 'analogy'. In an analogue signal, the voltage (say) on a wire corresponds to the motion of a microphone armature. There are many types of such 'transducer' that produce an electrical output that is proportional (ideally) to another physical quantity.
  5. Dec 15, 2012 #4
    Some interesting history.

    The use of the adjective "analog" in what we fondly call "analog electronics" began in the 1940s to differentiate the newly developed "digital computers" from the preexisting machines which subsequently became known as "analog computers".

    Prior to this, they were just called "computers", a term which could refer either to electrical apparatus or a room full of people armed with paper and pencil.
    Last edited: Dec 16, 2012
  6. Dec 16, 2012 #5


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    Your moniker is an interesting one, in this respect. I went to EMI (Hayes?) for a job interview in the mid 60s and saw an analogue computer (Emiac?) which was used in guided weapons development. I guess there would be a personal connection? I had done a course which included Op Amps, the year before and had looked at integrators for use in analogue computers. Then, in a room, we saw loads of steaming equipment which, at the time, was probably the quickest way of getting answers to target tracking problems with 'volts that were analogous to distances'.
  7. Dec 16, 2012 #6

    jim hardy

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    I always assumed it has same root as analogy,

    from Webster

    my slide rule being my favorite analog computer
    which operates on the inference that if distances along the C and D scales agree with base ten logartihms of numbers, they can be added and subtracted to agree with multiplication and division in base ten, just as can logarithms.

    I really enjoyed my analog computer lab where we solved differential equations with opamps and a strip chart recorder.

    Well, nowadays the term analog, when referring to a signal, is usually meant to describe its trait of having an amplitude (volts or milliamps) in proportion to the value it represents. That's in stark contrast to a digital signal which is a numerical representation by a string of numbers, usually just the 0's and 1's of the binary(base two) system, which decode to a number representing the value being expressed.

    Curiously there is now interest in computers with number bases other than binary. Base 3 arithmetic has a following, and so does base e. Try google.

    I once encountered a three level logic system, it used 0, 2.5 and 5 volts to represent 3 states. I was awed at the implications. If three levels, why not four or a hundred? Push that line of thought far enough, and at some very large number of states, digital computing would revert to analog.

    So the basic difference between analog and digital electronic signals is the number of levels used.
    An analog signal should be continuous over a range, ie an infinite number of levels;
    while a digital signal will have a discrete number of levels ,
    and nowadays that number is almost universally two. But watch out.

    Which begs the question - is output of a digital-to-analog converter really analog, if it can have only as many levels as its binary word allows ?

    just Sunday musings...

    old jim
  8. Dec 16, 2012 #7
    Well I think 'analog(ue)' as applied to electrical or mechanical signals is a contraction of the mathematical word 'analogical' meaning "In exact proportion to"

    It has a subtly different meaning in chemistry and biology.

    It has also come to mean those variables that are continuous between specified limits ie they can take on any numeric value to any precision between the limits.

    This is distinct from discretised variables, which may be digita (numeric)l or take on some other (non numeric) value such as 'open' or 'shut'.

    In physics we have quantisation or granulation of states, in mathematics we have 'concrete mathematics' or 'discrete mathematics' for similar terms.

    The terms have come to us from ancient Greek (analogon) through Latin (analogicus) and old French (analogie), which as Jim said has the same root as analogy.
  9. Dec 16, 2012 #8


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    The fact that so many digital channels can be fitted into the same spectrum space as one analogue channel is interesting. It works because there is a minimum step size in picture brightness or sound pressure that our senses can detect. This means that a version of the signal can be quantised. Other programme signals will fit into the spaces between these steps. In addition, there are methods of processing digital signals that utilise other 'holes' in pictures and sound that can be left out and approximated without causing unacceptable degradation. The analogue version contains stuff we just don't need.
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