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High Frequencies in Computer CPUs

  1. Nov 6, 2005 #1
    Hi Everyone,

    I just joined the forum and would like to extend a big hello to everyone! I had a look around the forum and it's a treasure trove of information. Congrats to everyone....

    I have a question that my father keeps asking and I don't know the answer to this one:

    Why don't the high frequencies (1Ghz-3.8Ghz) of computer CPUs interfere with signals from aerials for television? ie, watching TV in the same room on the VHF and UHF band. The aerial would be on the roof.

    Anyone know why this might be the case? :shy:
     
  2. jcsd
  3. Nov 6, 2005 #2

    Pengwuino

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    Welcome to the forum, refreshments are available in the back.... and watch out for the Evo :P

    Anyhow, as for your question, the "gigahertz" your computer talks about is different from the "gigahertz" a television is using. A television is recieving electromagnetic waves that are measured in hertz. When your TV recieves a 5gigahertz signal, it is recieving an electromagnetic wave in the air that is also 5gigahertz.

    A computer, on the other hand, rates the speed of its processors in hertz as well but not for the same process. 3,000,000,000 hertz (3ghz) means that the processor is making 3,000,000,000 calculations every second. It is not giving off any radiation at 3GHZ like a television is from the CPU.
     
  4. Nov 6, 2005 #3
    Couldn't have said it any better, Pengwuino :smile:.
     
  5. Nov 6, 2005 #4

    Integral

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    I am sorry Penquin, you are entirely wrong. The Gigahertz in a computer is EXACTLY the same as Gigahertz in a telephone or any other broadcast device. The single difference is power. The signal from a computer is very low power.

    Now, if you have ever taken the time to open your computer you may notice the copper fingers which surround the open side. The purpose of these is to provide a EM tight enclosure. If you do not have a good enclosure you CAN have interference with other electronic devices.
     
  6. Nov 6, 2005 #5
    Thank you!
     
  7. Nov 6, 2005 #6

    SGT

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    Really 3GHz is the frequency of the clock of the computer. Most operations use several clock cycles and a 3GHz computer makes considerably less than 3 billion calculations by second.
    And I agree with Integral that a poorly shielded computer could interfere with communications if it is near enough.
     
  8. Nov 6, 2005 #7

    rbj

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    which is one reason they want you to turn them suckers off in the airplane.
     
  9. Nov 6, 2005 #8

    Mk

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    vs.
    Penguino is right!! The GHz in a computer is how many calculations per second its microprocessor can do, whereas a TV's GHz has to do with the electromagnetic radiation.

    A Hz is simply 100 cycles per second.
     
  10. Nov 6, 2005 #9

    Pengwuino

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    Wait, so a telephone is recieving e/m radiation just like a television's reciever picks up broadcast signals (mind you, not cable TV, just normal broadcast bunny ears tv type signals)? I mean if we're talking about cable tv then yes you are right, however I don't understand how you are right if we are talking about broadcast signals from local stations wirelessly (like how a radio works).
     
  11. Nov 6, 2005 #10

    SGT

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    No, GHz is the frequency of the clock. Operations per second is flop (floating point operations). A computer able to do one billion operations per second would be labelled as 1 Gflop. Each operation needs, in general, several cycles of clock to be performed.
    No, 1 Hz is 1 cycle per second.
     
  12. Nov 6, 2005 #11

    Pengwuino

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    1 hz is 1 cycle per second
     
  13. Nov 6, 2005 #12

    Pengwuino

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    I thought it was the other way around, each cycle could do multiple operations...
     
  14. Nov 6, 2005 #13

    SGT

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    A wireless telephone receives EM radiation exactly as a radio or television receiver. The information (sound or video) modulates a high frequency carrier (hundreds of kHz in AM radio, tens of MHz to a few GHz in FM radio, television and cell phones). The signal is demodulated at the receiver in order to recover the information.
     
    Last edited by a moderator: Nov 6, 2005
  15. Nov 6, 2005 #14

    Pengwuino

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    I assume he meant a wired telephone or else i would have expected him to say "cell phone".
     
  16. Nov 6, 2005 #15

    SGT

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    Even in a wired phone, your voice is digitized and mixed with the voices of other people by modulating a high frequency carrier.
    And most people now use cordless phones. In a cordless phone, the base receives the incoming signal and uses it to frequency modulate a carrier and transmit it to the handset. The carrier frequency goes from several hundreds of MHz to a few GHz.
     
  17. Nov 6, 2005 #16

    Pengwuino

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    Yah but a television is recieving radio waves floating around in the air while wired telephones and computers are sending electronic signals through a wire/silicon track.
     
  18. Nov 6, 2005 #17

    Kurdt

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    The Hz rating of a Cpu tells you how fast the CPU clock is and not how many operations per second that CPU does. The operations per second has a relationship to the clock speed but also depends on the number of transistors the CPU has.

    Anyway basically the clock speed depends on the physical constraints the manufacture of the chip imposes. That is the time taken for the chip to complete one cycle of its computation (which generally takes more than one) is limited by how far apart the resistors etc are because it takes a finite time to send an electrical signal down a particular path.
     
  19. Nov 6, 2005 #18

    SGT

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    The current in a wire moves according to an electric field and the moving electrons generate a magnectic field, so in a wire, in the air or in vacuum we have allways a varying electromagnectic field.
     
  20. Nov 6, 2005 #19

    Integral

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    I do not have a cell phone but I do have older technology 900Mhz portable phones. These are so common that I do not even consider an old fashioned hard wired phone. To communicate with the base station my phone broadcasts a weak 900MHz signal.

    What ever speed your computer is operating at, mine is ~2GHz, that clock rate must be an actual signal produced by the motherboard. It is an electromagnetic signal carried mainly by the traces on the motherboard but it is impossible to constrain that frequency to the conductors alone. There will always be some power in electromagnetic radiation surrounding the conductors. This signal is essentially broadcast. It is a very weak signal but a signal none the less.
     
  21. Nov 6, 2005 #20

    Pengwuino

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    Well I'm talking about the old old old phones that are actually hard wired into the wall :D
     
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