Attenuation in notch filter

Discussion in 'The Projects Forum' started by Marie, Jan 8, 2008.

  1. Marie

    Thread Starter Member

    Nov 20, 2007
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    Hi,

    I'm currently working on the design of an active power filter and i've to use a notch filter to eliminate 50Hz component. I've managed to get a twin T notch circuit which in simulation is clearly eliminating the 50 Hz component. Unfortunately, there is an attenuation b/w the input and output voltage.

    I'ld like to know if it is the typical behaviour of a notch filter.

    I've attached a schematic as well as the graph of the input and output voltage.

    Thank you n Best wishes
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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  3. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    I noticed your notch was designed to attenuate appoximately 50 Hz [ 49.798 Hz ] but your signal generator is set to 150 Hz ... or am I reading your schematc diagram incorrecly?

    The scope output should replicate the input, only much lower amplitude, at the frequency you are rejecting.
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    Yes. You can see the phase-shift caused because the input signal is 150Hz and the notch is tuned to 50Hz.
     
  5. Marie

    Thread Starter Member

    Nov 20, 2007
    24
    0
    Thanks been there; indeed the pot has resolved my problem.

    About the 150Hz signal generator

    Sorry, i am new to forum and i can see that i'vent explain myself clear.

    Well in fact, i want to eliminate the 50Hz fundamental component and pass all the harmonics. This is why i set the generator to 150Hz to see if i could recover the harmonic signal without damping.

    Thanks a lot.
     
  6. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Marie,

    Not a problem.
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    You need to increase the Q of the filter so it rejects 50Hz but passes 100Hz and 150Hz without loss. The output voltage divider adjusts the Q.
     
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