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Thread: RF Amplifiers

  1. #1
    Newbie
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    RF Amplifiers

    Hi people what good are these amplifiers in boosting output and input signals?Does it really do its job?Seeing that they are so expensive I guess it does do its job.Could anyone please give some info on how it works and its application?

  2. #2
    Constant Bitrate
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    an amp must be coupled with an appropriate antenna for the job. An amp could be likened to an electric megaphone, sure, you can shout further, but the person you're talking to must be able to should equally loud for you to hear it. A directional antenna can be likened to one of the old-school pep rally megaphones. You can yell through it, and be heard louder, but you can also put that megaphone to your ear and hear far away things better. However, for automotive use, you want to be looking for signals all around you. A directional antenna would not be appropriate.
    An amplifier could assist in picking up weak signals, however, it may not. An amp would only be appropriate if you are having excessive cable loss to the antenna (which if done properly with correct cable and connectors, should never be the case). That being said, it would probably not be worth your while to spend the 250+ for an amp. I own a 1 watt amp and a .5 watt amp. I use both amps coupled with various different antennas, both omni and directional, depending on what I'm trying to achieve. I will most probably not being using an amp with my carputer wifi setup because my antenna will have enough gain to hit most APs. However, if I complete my stompbox-like project, I may use an amp with it.

    Another important thing to consider is the whole legality aspect.... The FCC code for wifi transmissions is that you are only allowed 4 watts of effective radiated power. I don't remember the formula offhand to determine what your radiated power is, but IIRC, for 500mw of power, you can only have something like a 8db antenna. It's not that much. I just found a page that has a couple handy charts to go by. http://www.wifihowto.org/?mo=HowTo;Item=9 Only the first chart would apply to automotive use, UNLESS you use a yagi, dish, grid, or similar HIGHLY directional antenna.

    Wow, what a mouthful. Hope this helps you in your quest for max range of wifi.
    Crawdaddy
    1991 Chevy Suburban 1500 w/SBC 350
    2005 Saturn ION 2 sedan

    Suburban Worklog

    "A local New Orleans man says his socks are finally dry..." -Tom Tucker, Family Guy

  3. #3
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    Another important thing to consider is the whole legality aspect.... The FCC code for wifi transmissions is that you are only allowed 4 watts of effective radiated power. I don't remember the formula offhand to determine what your radiated power is, but IIRC, for 500mw of power, you can only have something like a 8db antenna. It's not that much. I just found a page that has a couple handy charts to go by. http://www.wifihowto.org/?mo=HowTo;Item=9 Only the first chart would apply to automotive use, UNLESS you use a yagi, dish, grid, or similar HIGHLY directional antenna.

    Ok pal could you please explain this a bit more for me..I dont understand....Are u saying that I would not be able to use my 500mw adapter card with an antenna more than 8dbi of gain?please explain .........And i live outside the US so i dont know if it will still apply to me or if I would not be able to ship those items to my country...Please let me know thanks....and i am having problems finding the wifi fcc and iirc rules in google...

  4. #4
    Constant Bitrate
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    IIRC is shorthand for if I remember correctly. I did not say that you could not put more than an 8db antenna on it, just to stay legal you can't exceed 8db in the US with a 500mw transmitter. You can put as high of a gain antenna as you want on it, provided you don't exceed the input power of the antenna, which is usually FAR more that you could ever shove into it. you will want to check your country's regulations regarding wifi to determine what your maximum radiated power level is. Just keep in mind that even though the wifi card you're looking at is 500mw, putting a higher gain antenna on it will affect the effective radiated power, which is what regulations such as the FCC look at. I personally have exceeded 18+ watts of effective radiated power. However, I was using a directional antenna at the time, thereby bypassing the US FCC regulation of 4 watts EIRP.
    For car use, forget that directional antennas even exist, they're not suited to cars. Get an 8db omni and roll with that.
    Crawdaddy
    1991 Chevy Suburban 1500 w/SBC 350
    2005 Saturn ION 2 sedan

    Suburban Worklog

    "A local New Orleans man says his socks are finally dry..." -Tom Tucker, Family Guy

  5. #5
    Low Bitrate
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    Huntsville, AL
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    Hi platinumsteel,

    Maximum ERP for WiFi in Trinidad: 30dBm
    Maximum allowed antenna gain: 6dBi

    [media]http://www.tatt.org.tt/ddocs/BWASpectrum%20Plan.pdf[/media]

    pb

  6. #6
    Maximum Bitrate BarryWoods's Avatar
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    May as well install a microwave oven in your car without the door....
    Failure is not an option....



    It's installed by default on every version of Windows.

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