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Why do cell phones use 1800/1900 mhz?

Discussion in 'Electronic Basics' started by sf1, Oct 11, 2005.

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  1. sf1

    sf1 Guest

    when frequency is that large doesnt it mean shorter wavelength
    power line can travel 10000km because of extremely low frequenc
    doesnt it mean that cell phone signals travel very short distanc
    i dont understand this at all please hel
  2. Long wavelength implies a long distance with little phase shift. When
    you try to connect the same signal together at many points, like a
    power grid, it gets really messy if the waves coming around through
    the grid via different paths have different phases where they meet
    again. This causes big circulating energy loops in the grid.

    Cell phones do not use a grid of conductors, but make use of waves
    traveling through space. So the phase is unimportant when the waves
    reach a receiving antenna. All the various paths add together, and
    some effective phase results. But any phase will do, since the
    information being carried by those waves uses many cycles to carry
    each bit of information.
  3. Lord Garth

    Lord Garth Guest

    Yes, high (not large) frequency means a short wavelength. Very high
    frequencies are used to transmit data between the Earth and space probes
    which are also many thousands of km distant.

    Cell phones need to be compact and short range because they operate in
    CELLS which are limited geographical areas. They are also low power
    which helps extend battery life.
  4. Of course the cables used to transmit POWER have some bearing :)
    Whereas the whole idea of the cordless phones is just that, no cables
    trailing around behind you. The signal (very low POWER) is transmitted from
    a RF transmitter, there is extremely little actual POWER transmitted to the
  5. andy

    andy Guest

    One reason for using a high frequency is that high frequencies can carry
    more data per second than low frequencies. (Over to you to think about why
    this is). So a mobile phone mast can fit many 'virtual circuits' into
    one frequency band, and talk to lots of phones at once.


    Because that is the spectrum God gave them.

    You are correct that higher frequencies require more power to propagate an
    equal distance as say low band VHF. However, there is no room in those
    bands for cellular phones. Also there is no need with cell phones to reach
    out that far, (unless you live in South Dakota as I do) Also, Wavelength
    has a bunch to do with the antenna size. You do not want a 6 foot whip
    antenna on your cell phone or a large coil.
  7. Nog

    Nog Guest
    It's because the FCC said so. See ?
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