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Cell Phones

  1. Nov 18, 2009 #1

    tot

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    I was using my iPhone when I got to thinking about how amazing it is that so much information can be transferred all with electromagnetism.
    I was in a room with 500 other iphones and I could not connect at all.
    is this because AT&T could not support 500 people on the same tower?
    if someone with a verizion phone walked into the event would their phone work great?
    is there a limit to the amount of information that can be transfered on the Eletromagnetic field within a space?
    What frequencies do cell phone use?
    Can more than 1 cell phone be on the same frequency?
    How are there enough frequencies to go around?
     
  2. jcsd
  3. Nov 18, 2009 #2

    DaveC426913

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    Gold Member

  4. Nov 18, 2009 #3

    tot

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    thank you, I could not find this page with the search terms i used.
     
  5. Nov 18, 2009 #4

    DaveC426913

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    I Googled "cell tower" rather than "cell phone". :wink:
     
  6. Nov 18, 2009 #5

    tot

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    I wonder what frequency range AT&T has.
    Do you think that 500 connections would max out their frequency range.
    A bunch of people keep saying that AT&T is on 1900MHz

    THis is not a frequency range! do you think they are trying to say "Around 1900MHz"?
     
  7. Nov 18, 2009 #6

    tot

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    I wonder how easy it would be to tap in on Cell phone calls by picking up AT&T's frequencies.
     
  8. Nov 18, 2009 #7
    The same thing happened to me 2.
     
  9. Nov 18, 2009 #8

    DaveC426913

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    Last edited: Nov 18, 2009
  10. Nov 18, 2009 #9

    russ_watters

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    Staff: Mentor

    It is essentially impossible, since the information is digitally encoded and encrypted.
     
  11. Nov 19, 2009 #10
    There are several different cell phone frequency windows between 800 MHz and 2000 MHz. (not 300-400, that is incorrect.) iPhone supports a number of different bands, the ones used by AT&T in the U.S. are circa 850 and 1900 MHz. 1900 means 1850-1910 upstream and 1930-1990 downstream.

    The 850 MHz band has the bandwidth of 25 Mbps full-duplex per cell tower (this, obviously, can be increased through data compression), the 1900 MHz band is 60 Mbps full-duplex. This bandwidth is shared among all cell phones connected to the tower.
     
  12. Dec 6, 2009 #11

    tot

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    can you.. own the emfield?
    does AT&T own part of the emfield?
     
  13. Dec 6, 2009 #12

    jtbell

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    Staff: Mentor

    In the USA, the various sections of the electromagnetic spectrum are not "owned" by anybody. The Federal Communications Commission (FCC) regulates what different frequencies may be used for. They grant exclusive rights to certain frequencies to individual companies, for a fee.
     
  14. Dec 6, 2009 #13

    russ_watters

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    Staff: Mentor

    In other words, you lease the frequencies from the government.
     
  15. Dec 6, 2009 #14
    In other words, the government owns the frequencies.
     
  16. Dec 6, 2009 #15

    tot

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    that is so awesome that the government charges rent to use the electromagnetic spectrum. I hope the money gets sent into nuclear energy research.
     
  17. Dec 6, 2009 #16

    DaveC426913

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    You are right. It would be much better if we all used it as we saw fit.

    Personally, I am fond of a particular frequency and would use it all the time to run my wireless home network. The fact that it's the same frequency as is used by the nearby International Airport to land their planes is not really my problem. :wink:
     
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