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Analog Communication query

Discussion in 'Electronic Basics' started by Hollenburg, Jul 5, 2004.

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  1. Hollenburg

    Hollenburg Guest

    Hi,
    Recently in an interview one of my friend was asked some
    questions.....
    (1) If Digital Communication has so many advantages over Analog
    communication then why do we use Analog Communication. My friend
    answered simplicity to implement but they were looking for some more
    specific answers.
    (2) Physical realization of Phase Modulation.
    (3) Can a DC source be used as a supply to PC. [As far as I know.....a
    UPS does convert it to DC from the AC mains]

    Can anybody plzz give me the answer of these two
    questions...........Thanx.....Diba
     
  2. Rich Grise

    Rich Grise Guest

    Because it's there.
    Just make an ordinary reactance modulator and detune it a little.
    No, you need four.
    Why can't you ask the teacher? ;-)
     
  3. Captain

    Captain Guest

    Diba,

    There are two main reasons to study analog electronics:

    1) Everything actually transmitted is analog. This includes photonics and
    wireless. If you study, for example, a DSL transmission from your local
    telephone company's Central Office (CO) to your home, you will find that it
    consists of a series of tones, each of which is phase and amplitude
    modulated to carry a digital byte. The contents are digital, but the actual
    transmission is totally analog. The drivers which send the signal down the
    line are analog, as are the receivers at the other end.

    So, all communication is actually analog in nature, In fact, digital
    communications are always carried on an analog medium.

    2) Your friends are actually quite correct. So look for examples of the
    greater simplicity of analog.

    As to the other two, come on now, look them up! Hint - Quadrature Amplitude
    Modulation -

    Cap
     
  4. Bob Myers

    Bob Myers Guest

    Well, not quite. This touches on one of my personal hot buttons, which
    is a widespread confusion about that the terms "analog" and "digital"
    really mean.

    "Analog" does NOT equate to either "continuous" or "linear", and in
    fact there are examples of "analog" communications schemes which
    are neither. "Analog" simply means that the information being carried
    is encoded on to the signal in such a way that a given parameter of
    the signal - the voltage, say - is varying in a manner that is
    *analogous* to the original information. In an AM radio signal, for
    instance, the amplitude of the carrier is changing in a manner analogous
    to the variations in the original sound waves. In a standard analog video
    signal, the voltage of the signal varies according to the luminance in
    the original image. It is incorrect to say that "everything is analog" from
    this perspective, just as it is incorrect to say that "everything is really
    digital" (often heard from those who are invoking the discrete nature
    of things, per quantum mechanics and such). "Digital" simply means
    that the information is being encoded in such a way that the signal
    states are to be interpreted as corresponding to numeric values (or
    more broadly, some other such symbolic representation) rather than
    being a "drawing" of the original information.

    The reason we study "analog" communication has to do with an
    incorrect assumption that is embedded in the original question.
    "Digital" communication is NOT inherently superior in all aspects
    as compared with "analog" communication; the superiority of one
    over the other depends on the specific requirements of the application
    being considered, and the specifics of the encoding schemes, analog
    OR digital, being compared. What most people think of as
    "digital" communications (straight binary encoding, transmitted
    serially in a given channel) typically will have advantages in terms of
    noise immunity, but it actually horribly inefficient in terms of its
    efficiency
    - the amount of information that can be transmitted per second in a given
    bandwidth. It also suffers from a sort of "cliff effect" vs. many common
    "analog" schemes - meaning that this form of digital communications will
    remain essentially "perfect" (lossless) right up to a certain limit in the
    noise
    level - beyond which, EVERYTHING is lost (as opposed to common
    analog systems, which degrade more gracefully in the presence of noise).

    So - the bottom line here is that it just ain't that simple. We study both
    analog AND digital communications because each still has its place.
    There's really no such thing as an "analog" or "digital" SIGNAL, when
    you get right down to it - it's all just electricity or EM waves. What
    makes
    it "analog" or "digital" is the method used to encode the information
    carried by that signal, and therefore how it is supposed to be interpreted
    by the receiver.


    Bob M.
     
  5. Dbowey

    Dbowey Guest

    Bob posted:
    Well, not quite. This touches on one of my personal hot buttons, which
    is a widespread confusion about that the terms "analog" and "digital"
    really mean.

    "Analog" does NOT equate to either "continuous" or "linear", and in
    fact there are examples of "analog" communications schemes which
    are neither. "Analog" simply means that the information being carried
    is encoded on to the signal in such a way that a given parameter of
    the signal - the voltage, say - is varying in a manner that is
    *analogous* to the original information. In an AM radio signal, for
    instance, the amplitude of the carrier is changing in a manner analogous
    to the variations in the original sound waves. In a standard analog video
    signal, the voltage of the signal varies according to the luminance in the
    original image. It is incorrect to say that "everything is analog" from this
    perspective, just as it is incorrect to say that "everything is really digital"
    (often heard from those who are invoking the discrete nature of things, per
    quantum mechanics and such). "Digital" simply means that the information is
    being encoded in such a way that the signal
    states are to be interpreted as corresponding to numeric values (or
    more broadly, some other such symbolic representation) rather than
    being a "drawing" of the original information.

    The reason we study "analog" communication has to do with an
    incorrect assumption that is embedded in the original question.
    "Digital" communication is NOT inherently superior in all aspects
    as compared with "analog" communication; the superiority of one
    over the other depends on the specific requirements of the application
    being considered, and the specifics of the encoding schemes, analog
    OR digital, being compared. What most people think of as
    "digital" communications (straight binary encoding, transmitted
    serially in a given channel) typically will have advantages in terms of
    noise immunity, but it actually horribly inefficient in terms of its
    efficiency - the amount of information that can be transmitted per second in a
    given bandwidth. It also suffers from a sort of "cliff effect" vs. many common
    "analog" schemes - meaning that this form of digital communications will
    remain essentially "perfect" (lossless) right up to a certain limit in the
    noise level - beyond which, EVERYTHING is lost (as opposed to common analog
    systems, which degrade more gracefully in the presence of noise).

    So - the bottom line here is that it just ain't that simple. We study both
    analog AND digital communications because each still has its place.
    There's really no such thing as an "analog" or "digital" SIGNAL, when
    you get right down to it - it's all just electricity or EM waves. What
    makes it "analog" or "digital" is the method used to encode the information
    carried by that signal, and therefore how it is supposed to be interpreted by
    the receiver.
    I believe that a designer who understands electronics will not think in terms
    of "what's analog and what's digital." She/he will use whatever design skills
    will get the job done.

    Speaking of hot buttons, you make a false statement in
    "In an AM radio signal, for instance, the amplitude of the carrier
    is changing in a manner analogous to the variations in the original
    sound waves."

    The Carrier does not vary - it is constant. The sidebands, which are generated
    in the process of modulation, are analogous to the original audio signal.

    Don
     
  6. Bob Myers

    Bob Myers Guest

    Sure - but the sign on the door here is still "sci.electronics.basics",
    and I was assuming from the original post that we weren't exactly
    working at the "experienced designer" level.
    True, and a good point; however, again that's the way it's normally
    thought of at the beginner level, and you don't really get to the
    constant-carrier-amplitude (or rather, the presence of a constant-
    amplitude component at the carrier frequency in the transmitted
    signal) idea without a bit more understanding of the math than you'll
    usually get in the "AM in one paragraph" sort of description. THERE,
    you get the standard time-domain "scope display" sort of picture,
    with an RF signal whose amplitude is varying with the audio.

    Bob M.
     
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