Decibel help

Discussion in 'Homework Help' started by c2morg, Feb 4, 2004.

  1. c2morg

    Thread Starter New Member

    Feb 4, 2004
    2
    0
    hi everyone, im stuggling to keep my head above water in the course im doing, hope you can help !

    the questions goes - oh and im not looking for an answer, that will get me no where, but if someone could walk through it, that would be amazing !! ;)

    "Calculate the voltage measured across a 600 ohms load for power level of 0dBm"

    Im ok with working out directly each of ohms laws, and pretty ok with minor decibel stuff, but I just dont even know where to begin with this !
     
  2. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    144
    Are you familiar with:

    Votage Ratio in dB = 20*log(base 10)[V1/V2]

    I am trying to remember whether the voltage ratio is taken as a reference to dBw or dBm, at which case you would have to convert from dBm in your example, to dBw.

    For 600dBm:

    dBw = 10*log(base 10)(0.6) = -2.218 dBw

    It is along time since I did this so I'm a little rusty :blink:
     
  3. c2morg

    Thread Starter New Member

    Feb 4, 2004
    2
    0
    cheers m8

    been taking a stab at it, i remember the formula

    right

    remember that P= V2 / R (voltage squared) / resistance

    swap it too v2 = p x r power X resistance

    uve got the resistance ®600

    times

    power(p) 1mw-(reference) (0dBm is equal and a referance to 1mW remember!)


    =0.6v


    square routed=.775v


    anyone verify im completly wrong and dave is right ?
     
  4. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    144
    I'll go with your answer c2morg, I think I'm venturing up the wrong tree with my response. And I can't see a problem with your calculation.

    Good effort :D
     
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