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How do these both relate to one another? (Gain and dB's)

  1. Jun 16, 2016 #1
    I have tried to look at how these, gain and dB's, relate to one another, but there seems to be nothing solid on the Internet. Perhaps I am looking in the wrong places.
  2. jcsd
  3. Jun 16, 2016 #2
    Just a thought: Could it perhaps relate to the gain or loss in power?
  4. Jun 16, 2016 #3

    jack action

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    Was that clear enough?
  5. Jun 16, 2016 #4


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    Jack is correct. But even simpler, dB is just a relative shorthand that is often used to describe gain. Nothing more. It is often used instead of the linear value because it leads to smaller numbers (instead of dealing with numbers like 1000 or 1 million you have 60 dB or 120 dB) and it makes certain mathematical operations simpler to do in your head.

    Keep in mind that dB doesn't inherently have anything to do with gain, it is just a shorthand. People use dBs for other things with wide spreads in value for example isolation, noise, or relative level of harmonics in a signal.
  6. Jun 16, 2016 #5


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    taken a little further, there is ....
    voltage gain = VoltageGain = 20 Log10 x Vin /Vout in dB
    Power gain = Power in WattsGain = 10 Log10 x Pin /Pout in dB

    note voltage is 20 x Log10 and power is 10 x Log10

    for power gain and particularly when working with RF and amplifiers gain is usually related to a standard level ( a reference level)

    this may be 0dBm = 1 mW or say 0dBW = 1W
    so if using the 0dBm reference, a gain of 10dBm = 10mW, a gain of 20dBm = 100mW, a gain of 30dBm = 1000 mW (1W), a gain of 50dBm = 100,000 mW = 100W

    you quickly see that this is a logarithmic scale

    analogdesign's example of 1000 = 60dB is for a voltage remembering it is 20 x Log10 and not 10 x Log10 that is used for power

    Last edited: Jun 16, 2016
  7. Jun 16, 2016 #6

    jim hardy

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    Sometimes it's tricky to get all the way down to the basics. Computers are just too nitpicky ...

    Do you understand that "gain" implies a ratio ?
    Alexander Graham Bell used the ratio 10 to 1 in his work and got a unit named after him, the "Bel" with just one "l" .
    It stands for a power ratio of ten and is basic to sound measurement. We measure intensity of sound with logarithms because the ear is capable over such a wide range of loudness.

    Try a search on that term, maybe it'll cement the idea in place for you.
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