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    Decibel and Noise

    Uploaded by

    tsikboy
    The decibel scale is used in communication systems to compress the wide range of signal magnitudes into easier to work with numbers. It is a logarithmic scale defined by power or voltage ratios in decibels. Noise, which is any unwanted interfering signal, is often measured in decibels relative to the desired signal. There are different reference values used with decibels such as dBm, which is referenced to 1mW, dBW to 1W, and dBV to 1V. Decibels can be added or subtracted directly when working with the same reference but require conversion when combining values with different references.

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    Decibel and Noise

    Uploaded by

    tsikboy
    19 views2 pages
    The decibel scale is used in communication systems to compress the wide range of signal magnitudes into easier to work with numbers. It is a logarithmic scale defined by power or voltage ratios in decibels. Noise, which is any unwanted interfering signal, is often measured in decibels relative to the desired signal. There are different reference values used with decibels such as dBm, which is referenced to 1mW, dBW to 1W, and dBV to 1V. Decibels can be added or subtracted directly when working with the same reference but require conversion when combining values with different references.

    Original Description:

    signal in decibel

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    The decibel scale is used in communication systems to compress the wide range of signal magnitudes into easier to work with numbers. It is a logarithmic scale defined by power or voltage ratios in decibels. Noise, which is any unwanted interfering signal, is often measured in decibels relative to the desired signal. There are different reference values used with decibels such as dBm, which is referenced to 1mW, dBW to 1W, and dBV to 1V. Decibels can be added or subtracted directly when working with the same reference but require conversion when combining values with different references.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    19 views2 pages

    Decibel and Noise

    Uploaded by

    tsikboy
    The decibel scale is used in communication systems to compress the wide range of signal magnitudes into easier to work with numbers. It is a logarithmic scale defined by power or voltage ratios in decibels. Noise, which is any unwanted interfering signal, is often measured in decibels relative to the desired signal. There are different reference values used with decibels such as dBm, which is referenced to 1mW, dBW to 1W, and dBV to 1V. Decibels can be added or subtracted directly when working with the same reference but require conversion when combining values with different references.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 2

    @pinoytsikboy

    Decibel

    Signals in communication systems span a range of extremely wide magnitude. The
    decibel scale, which uses ratios and logarithms, compresses this wide span into smaller,
    easier to manipulate range of numbers.

    Noise any unwanted, interfering signal is a serious problem with communication
    systems. It is often measured in decibels in relation to the desired signal.

    Decibel a convenient logarithmic scale to overcome wide range of values in
    communication systems. The equation define the dB scale for power

    dB = 10 log
    O
    P
    P
    1

    Where : P
    1
    and P
    o
    are power ratios

    In voltage ratios,
    dB = 10 log
    2
    2
    2
    1
    V
    V

    = 20log
    2
    1
    V
    V


    Note: When using the dB scale with voltage or power, the voltage or current must be
    measured at points with the same equivalent resistance.

    signal power or voltage are equal, the relative value is 0 dB.
    A twice power (P
    1
    = 2P
    o
    ) , the dB ratio is 3 db.
    At half-power (P
    1
    /P
    o
    = 0.5), the dB ratio is 3 dB. (Half-power point)
    A percentage gain or loss can be expressed in dB.
    + dB = gain
    - dB = loss

    dB Reference values

    dB is the ration of two power or voltage values, not an absolute unit of measurement of
    volt or watt. As a result of this shortcoming, several reference values are use in the
    industry. This means that all dB values are stated is relative to a given standard value.

    Using 1 mW (0.001 W) as reference:

    dBm = 10 log
    mW
    P
    1
    1
    = 10 log
    001 . 0
    1
    P



    @pinoytsikboy
    Using 1W as reference:

    dBW = 10 log
    W
    P
    1
    1


    Using 1 V as reference:
    dBV = 10 log
    V
    P
    1
    1


    Addition and subtraction of dB:

    1. dB dB = dB
    total
    (direct addition or subtraction)
    example:
    1. 1 dB + 2 dB = 3 dB (gain)
    2. 1 dB 2dB = -1 dB (loss)

    2. dB dBm = dBm
    total

    example:
    1. 1 dB + 2 dBm = 3 dBm (gain)
    2. 1 dB 2dBm = -1 dBm (loss)

    3. dBm dBm = (cannot be added/subtracted directly)
    example:
    1. 1 dBm + 2 dBm =

    1 dBm = 10 log (Po/ 0.001)
    Po =(0.001)x log
    -1
    10
    1
    = 1.25 mW

    2 dBm = 10 log (P1/ 0.001)
    P1 =(0.001)x log
    -1
    10
    2
    = 1.585 mW

    Then add Po and P1 : Pt = 1.25 mW + 1.585 mW = 2.84 mW

    Use 1mW as reference: dBm = 10 log
    mW
    mW
    1
    84 . 2
    = 10 (0.4553) = 4.55 dBm

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