computer signal is it digital or analog

Discussion in 'Computing and Networks' started by jblueink, May 31, 2008.

  1. jblueink

    Thread Starter Member

    May 27, 2008
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    my question is computer signal, thats the signal sent and received by computers system are they in digital or analog.but computer work with digit. the communication between the ground based stations and the space satellite is what kind of communication and also what kind of signal is used?
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Computers use digital signals to communicate between the internal and peripheral devices. Some devices, like the modem and the sound card, output and receive analogue signals, but they convert these analogue signals to digital signals by using DAC (sound card) or FSK (modem). Thus they still communicate with digital signals with the PC. For the communication between the earth and the satellites they use microwaves as far as i know.
     
  3. StephenDJ

    Active Member

    May 31, 2008
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    The concept of "off" or "on" (0 or 1) is the very foundation on which a digital computer is built. In a computer, regular voltages may be used to represent these states, but in order to transmit these states without wires over long distances, a constantly changing analog signal may be needed to represent the 0s and 1s which are digital. This process is called modulation, and it can exist in the format mik3 mentioned above (FSK) or any of other many different formats. (Hope this helps.)
     
  4. jblueink

    Thread Starter Member

    May 27, 2008
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    thanks. but one more thing what is FSK.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    Frequency shift keyed. One tone for logic high, another for low. Google is really great for finding out about these things.
     
  6. Dave

    Retired Moderator

    Nov 17, 2003
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  7. sax1johno

    Member

    Oct 20, 2007
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    "the communication between the ground based stations and the space satellite is what kind of communication and also what kind of signal is used?"

    It honestly depends on the system . . . but on modern systems, the uplink (to the satellite) is always digital because it has to be encrypted (you can't encrypt analog signals reliably or quickly).

    Modern satellite systems use Binary uplinks (to the satellite) and downlinks (to the ground station) using phase-shift-keying (PSK) -- check out google for that one. The signal is often in the Ku-band, C-band, or X-band -- but it is not necessarily limited to that. Also, the signal is almost always polarized.

    Commanding of satellites especially relies on encrypted binary for the uplink -- otherwise you could have people sending commands to the satellites, which could really wreak some havoc. As for the downlink, subscription services like XM and DirecTV have encrypted downlinks, GPS and FTA (Free-to-air) television and radio are not encrypted.
     
  8. sharma2k7

    Active Member

    Dec 10, 2007
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    Communications inside computer are pure digital communication, Digital data over Digital medium.LAN Communications are digital data over analog medium AM & FM's are analog data over analog medium,When we talk about Digital system Usually we are talking about Digital information over Analog medium.
     
  9. StephenDJ

    Active Member

    May 31, 2008
    58
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    In reference to what is FSK, often a zero-crossing detector is used in hardware to detect when the analog signal voltage passes through zero-volt level as it rises and falls. Every time it crosses zero twice (rise/fall), a cycle is detected. The rate at which it does this is how the frequency is detected. For example, 1200 Hz could represent a logic 0, while 2400 Hz could represent a logic 1.
     
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