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Homework Help: Link Budget

  1. Dec 7, 2012 #1
    1. The problem statement, all variables and given/known data
    A signal needs to be transmitted over 1.1km, with 12Hkz bandwidth on FM carrier.
    Carrier freq=875MHz.
    Allowed up to 1W carrier power transmitted and received thru omnidirectional antennas.
    antennas low loss, max attenuation = 0.1dB

    2. Relevant equations

    Received Power (dBm) = Transmitted Power (dBm) + Gains (dB) − Losses (dB)

    3. The attempt at a solution

    I'm beat
    Last edited by a moderator: Dec 7, 2012
  2. jcsd
  3. Dec 7, 2012 #2


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    Staff: Mentor

    Well, at least you listed a Relevant Equation. That's good.

    Now, what can you fill into that equation? What are the losses for example?
  4. Dec 7, 2012 #3
    are the losses the free space path losses?

    is the gain the attenuation ie G -0.1dB?

  5. Dec 7, 2012 #4


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    Staff: Mentor

    What is "875000000)/300000000"?

    The gain would be any antenna gain, but you are told the radiation is isotropic, so there is no gain.

    It looks like you are trying to calculate the loss by using the surface area of a sphere of 1100m radius, which is correct. The 0.1dB would be an additional antenna loss to add in.

    1Watt is 1000 times 1mW, so yes, that would be 10*log(1W/1mW) = 30dBm.

    EDIT -- BTW, the question does not make it clear if it is 0.1dB max loss per antenna or for the two antennas as a system. You should see if you can clarify that (it oly changes your answer by 0.1dB, but it would be good to get it right the first time).
  6. Dec 8, 2012 #5

    using ((4*pi*d*f)/c)^2=FSPL

    10log(FSPL)= losses in dB = 92.1dB

    assuming 0.1dB attenuation per each antenna

    Received Power (dBm) = Transmitted Power (dBm) + Gains (dB) − Losses (dB)
    Pr=30dbm + 0 - 92.1dB - 0.2dB

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