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Volt/meter to decibel

  1. Mar 14, 2010 #1
    I have a table containing the magnitude (dB) of an electric field referred to 1 volt/meter.
    The values range from 112 to -36dB. How can I properly interpret the attenuation loss in each case in this table? In other words, for a reference of 1 volt/meter and no signal loss, what is the expect value in dB?
     
  2. jcsd
  3. Mar 14, 2010 #2
    Try

    dB = 20Log(V2/V1), or

    V2/V1 = 10^(dB/20)

    A change of a factor of two is

    20Log(2) = 6.02 dB

    Bob S
     
  4. Mar 14, 2010 #3
    If the reference is 1 volt/meter then one would expect that to be equal to 0 dB. However 112 dB referenced to 1 volt/meter seems unreasonably high. Are you sure the reference wasn't to 1 microvolt/meter?
     
  5. Mar 14, 2010 #4
    Hi skeptic2, completely sure about 1V/m, that is why I did not understand.
     
  6. Mar 14, 2010 #5

    sophiecentaur

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    What is the context of the table?
    If it is simply tabulating a mathematical relationship there need be no problem. If it it supposed to relate to some physical situation then it seems to have some rather high values: nearly 0.5 MV/m! Hardly a "signal" strength!
     
  7. Mar 14, 2010 #6
    I made some research and figure out the following: 1V/m= 0 dB[tex]\mu[/tex]V/m.
    Therefore, the values I am seeing in the table correspond conversions of this reference. If the signal is not attenuated, I have 1V=1*106*[tex]\mu[/tex]V and 20log(V2/V1) in this case is 120. A value of 112dB means that the attenuation is 8dB. I believe this is the explanation.
     
  8. Mar 22, 2010 #7

    sophiecentaur

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    But that definition of the dB is not right.
    1V/m is 0dBV/m
    or
    1V/m is 120dBmuV/m
    That's an identity, surely.

    That assumes the same impedance. dB is actually a log of power ratio.
     
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