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Gps, Mobile phones microwaves and radiowaves

  1. Dec 19, 2008 #1
    Hello, friends!
    I've google about the question below but no success!
    The question is:

    Gps signals inside buildings are nonexistent or very weak, but mobile phone and am and fm radio signals are good, so the question is: why gps satellites and mobile phone comunications don't use emission on the radiowave band, which is less dangerous for our health.

  2. jcsd
  3. Dec 19, 2008 #2


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    Staff: Mentor

    I suspect that GPS needs a higher frequency because of the accuracy of the signal, but it is still in the radio wave part of the spectrum. As are cell phone signals.

    Also, there really aren't any health issues here.
  4. Dec 19, 2008 #3


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    Homework Helper

    Also, noise and digital modulation are big (related) issues.
  5. Dec 19, 2008 #4


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    Science Advisor

    I donn't think it's a matter of the frequencies used; I think it is a difference in power of the signal. GPS signals have to come all the way from the sattelite to the Earth, cell phones and radios only have to make it from the tower to where you are.
  6. Dec 19, 2008 #5
    National and international agreements are necessary for the use of different frequencies to avoid inteference....and signal characteristics have pros and cons in different applications...
    see http://www.mlesat.com/Article9.html

    for additional information....note satellites are allocated Ka, Ku, and C bands...and only so much spectrum is available.
  7. Dec 19, 2008 #6


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    Partly it's the frequency - in general lower frequency (longer wavelengths) penetrate further.
    AM radio has the lowest frequency <0.5MHz and penetrates furthest, FM at 100MHz less far.
    Mobile phones use 900 or 1800MHz and only go a short distance into a building depending on the construction. But mobile phones are relatively powerful signals.

    GPS uses 1500MHz so has similair characteristics to a cell phone but much lower power. It also relies on accurately measuring the signal from a number of satelites to get a position which is difficult if some signals are reflected or blocked.
    A phone conversation is intelligible even with very poor signal to noise.

    Cell phones, bluetooth, and Wifi are all in the microwave band,
    Last edited: Dec 19, 2008
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