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different dbi for antenna and repeater

Discussion in 'Phantom 2 Vision + Mods' started by aristosv, Sep 21, 2014.

  1. aristosv

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    What happens when I have an 8 dbi antenna connected on my repeater, but I have the repeater working on 12dbi?
    Will the repeater get damaged? Or will the signal be worst than it would be if it was configured at the same dbi as the antenna?
     
  2. itchybeard

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    Mmmmmm, I think you mean that you have an 8dBi antenna, but the repeater is working on 12dBm

    Perhaps this will help you ....

    http://www.dslreports.com/faq/14091
     
  3. aristosv

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    wow that article confused me even more. now i really have no idea what antennas should i get for my p2v+ repeater
     
  4. rrmccabe

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    Are you asking what happens if you use a different antenna gain (dbi) on the TX vs the repeater?
     
  5. aristosv

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    No, I am asking what happens when the antenna connected on the repeater is 8dbi, and the repeater is configured to be working on 12 dbm.
    Keep in mind that I don't know the relevance between dbi and dbm...so i don't know if i'm asking a stupid question.
     
  6. itchybeard

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    As long as the antennas are rated to handle the power coming from the repeater then you can use whatever dBi (gain) you want.

    Example: The stock DJI RC controller in FCC mode is rated at 20dBm, but it only has a 3dBi antenna. However the antenna is capable of handling 20dBm (100 milliwatts). Just check the spec sheet of the antenna you want to use and make sure it can handle the RF power you are going to put through it.
     
  7. aristosv

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    Can you point me to guide explaining the relation between dbm, milliwatts and rf power?
     
  8. itchybeard

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    LOL.

    They are all different ways of descibing the same thing. Try google. Most places selling antennas will publish the spec and most antennas will handle far more than 12dBm.

    I was thinking about getting a pair of these handy little omnis for the 5.8Ghz connection on my Phantom.

    http://rf-links.com/newsite/antennas/5800.html

    If you click on "more info" you'll see that they only weigh 3grams and can handle a maximum input power of 2 watts which is far more than the 63 milliwatts that I want to put through them.

    Look at this for more info ....

    http://www.cpcstech.com/dbm-to-watt-con ... mation.htm
     
  9. aristosv

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    So as the transmitter's dbm go higher, the antenna's dbi go lower? That means for example that if i have a 2watt booster on my phantom controller, i can use an antenna with lower than 6 dbi? (According to that last chart).

    I was under theh impression that i have to match the antenna's dbi to the transmitter's dbm. (Which is only true for the 24 dbm)
     
  10. itchybeard

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    No, aristosv, you still don't get it.

    By increasing the gain (dBi) of an antenna you are focusing the power of the transmitter in the direction you want the beam to go, but you are also narrowing the beam so you have to aim a high gain antenna (bigger dBi number) more carefully than a low gain antenna (smaller dBi number) because you lose coverage in other directions.

    A low gain antenna gives you better coverage in all directions, but has less range in the direction you want the beam to go.

    You do not have to match the antenna's dBi to the transmitters dBm.
     

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  11. aristosv

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    Ok, this was helpful.

    Its strange though because yesterday i bought an 8dbi antenna that tplink sells as omnidirectional.
     
  12. itchybeard

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    Yes, it is omnidirectional, aristosv. This means that the beam is shaped like a "doughnut" and goes all around the antenna, but with a high gain antenna the doughnut is squashed. This means it spreads out further but it doesn't go very far above or below the antenna.

    Have another look at the diagram.