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Who knows cell phones and antennas?

Discussion in 'Electronic Basics' started by Eric R Snow, May 4, 2005.

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  1. Eric R Snow

    Eric R Snow Guest

    Greetings,
    Even though this is the basic group, my knowledge is less than basic
    but there are some pretty advanced folks here. So here's my question:
    How to increase range of cell phone while in remote areas. I have a
    little motorola flip phone. It has a stubby little antenna that works
    great around the city and I-5 corridor but has spotty reception on the
    island I live on north of Seattle. But I'm always hearing about
    stranded hikers using cell phones to call for help in the Cascade
    mountains around the Seattle area. So I was wondering what kind of
    antenna booster could be made so that when I fall down a hill and
    scrape my knee I can call for rescue. I thought about getting a car
    antenna but don't know if the car has to be present for it to work
    properly. Anybody know the answers?
    Thanks,
    Eric R Snow
     
  2. Joel Kolstad

    Joel Kolstad Guest

    Being literally on a mountain is a huge advantage to any radio system in that
    you have a direct line of sight 'connection' to a cell tower.
    Since you're asking this question, a safe answer is that you simply can't
    build one yourself. However, if you do a little Googling you'll find that
    commercial amplifiers are available. But keep in mind the following: Just
    adding an amplifier lets the cell tower hear YOU better, but doesn't allow you
    to hear IT any better whatsoever! The reason that "antenna boosters" can
    improve performance is due to the fact that the cell towers output much more
    power than your phone (often tens of watts vs. a decent fraction of a watt).
    The other reason they work is that they always use an external antenna, which
    are electrically bigger (more gain) and which can typically be placed higher
    up (e.g., on a roof) and therefore can also "see" the towers better. Finally,
    with a _directional_ antenna, you've got the one thing that'll let you hear
    the tower better.
    Most car antennas are simply dipoles using the card as the ground plane (more
    or less), so using a car antenna on a decent sized slab of sheet metal is
    fine. These antennas aren't directional (since this isn't practical in a car
    that's pointed in arbitrary directions from minute to minute!), but for a home
    installation you can special order directional antennas.

    This is what I'd do:

    -- Get a cheap external 'car' antenna for the phone. Put it up as high as you
    can somewhere, see if it helps.
    -- If not, and assuming you have line of site to a cell tower, get a
    directional antenna. So-called "Yagis" are standard and can easily quadruple
    the workable distance between the phone and the tower.
    -- If not, start looking at amplifiers.

    ---Joel
     
  3. PeteS

    PeteS Guest

    Although you can use those antennae, keep in mind that the cell system
    actually controls the output power of your phone - when you are close,
    *your* phone is commanded to reduce it's output power, although the
    cell may or may not reduce *it's* power. If your problem is related to
    being in a very poor signal area, then using an antenna with a greater
    physical area (but the same electrical area - there's a lot of trickery
    in antenna design) may well help.

    Cheers

    PeteS
     
  4. Rich Grise

    Rich Grise Guest

    4. If you're going hiking in the wilderness, bring along proper equipment.
    4a. Don't jump off cliffs. ;-)

    Good Luck!
    Rich
     
  5. Eric R Snow

    Eric R Snow Guest

    The antenna, of course, is to be part of the proper equipment. As far
    as jumping off cliffs go, I'll do whatever I want! So There!
    Cheers,
    Eric
     
  6. Rich Grise

    Rich Grise Guest

    In some parts of the world, people get billed for the expense of frivolous
    rescues.

    Anyway, to answer your original question, I wouldn't want to try to add a
    home-brew antenna to a cell phone, unless you know of some way to get
    proper matching and everything. I seriously doubt if you have access to
    adjust the output circuit. It might be worthwhile to look into some kind
    of long-range phone, or even get a ham license. :)

    Good Luck!
    Rich
     
  7. Joel Kolstad

    Joel Kolstad Guest

    Rich,

    In my experience, most (but certainly not all) cell phones have antenna
    connectors on them (often blocked by a rubber plug or something, however),
    just waiting to have a proper connector/coax cable plugged into them.
    (Usually MMCX or similar...)

    ---Joel
     
  8. Eric R Snow

    Eric R Snow Guest

    Yes, my phones antenna screws out. I'll check and see if there is a
    longer range antenna that screws right in. Id been so het up on making
    my own, just for fun, that I didn't even remember that the stubby
    little antenna unscrews. Thank you and the others that have replied.
    Cheers,
    Eric
     
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