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dBm, dBu, dBc?

Discussion in 'Electronic Basics' started by sck0006, Nov 16, 2005.

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  1. sck0006

    sck0006 Guest

    Correct me where I am wrong, please.

    dBm, decibel with reference of 1mW (at specified impedance)

    dBu, decibel with reference of 1uV

    What in God's name is dBc? This is in RF frequencies at 50 Ohm
    impedance. I've seen it in a few service manuals, usually in relation
    to harmonic levels. Please straighten me out, I would greatly
    appreciate it.

    Thanks,
    Steve
     
  2. Pooh Bear

    Pooh Bear Guest

    No. That would be dBuV.

    dBu is a voltage based measure used in ( pro ) audio where 0dBu is 0.775V.

    Graham
     
  3. Bob Monsen

    Bob Monsen Guest

    http://www.google.com/search?hl=en&lr=&c2coff=1&oi=defmore&defl=en&q=define:dBc

    ---
    Regards,
    Bob Monsen

    A great truth is a truth whose opposite is also a great truth.
    - Niels Bohr
     
  4. John Larkin

    John Larkin Guest

    Db relative to carrier power level.

    John
     
  5. sck0006

    sck0006 Guest

    Thank you everyone, it makes perfect sense now.

    In response to dBu, dBuV.. I have a spectrum analyzer, an esa-1000,
    and it uses dBu for all its measurements. Is this actually dBuV, just
    abbreviated? Thanks again for the replies... Steve
     
  6. Pooh Bear

    Pooh Bear Guest

    It must be.

    The dBu ( for audio ) was 'invented' in the mid 70s to replace the by then
    misused dBm( 600 ohms) for voltage based measurements of audio signals..
    Audio circuits had long ceased to use 'matched impedance working' for a host
    of practical reasons.

    The IEC defines decibel units. Most consist of dB+ reference level.

    E.g....

    dBV ( volts )

    dBW ( watts)

    dBm ( milliwatts ) ( + reference impedance ) - the W is inferred -
    presumably for historical reasons

    Graham
     
  7. sck0006

    sck0006 Guest

    Makes sense. Thanks for the great replies!
    Steve
     
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