Linear sweep to logarithmic sweep

Discussion in 'General Electronics Chat' started by relicmarks, Nov 17, 2008.

  1. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    How do u change or what changes a oscillator or LFO from a linear sweep to a logarithmic sweep?

    My function generator has only a linear sweep, how can i make it logarithmic sweep?

    Inside a function generator , what makes the sweeping circuit?
    a.) is it a LFO circuit tied to a LED/LDR circuit?
    b.) how does it sweep the frequency parameter resistance?

    How do u know when a AC sinewave or triangle waveform is logarithmic or linear?
     
  2. studiot

    AAC Fanatic!

    Nov 9, 2007
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    513
    If you pass a linear sweep voltage ramp through an op amp with a diode in the feedback loop the output approximates to a logarithmic sweep.

    Some commercial sweep generators have an external sweep input for this.

    Look up 'logarithmic convertor'
     
  3. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
    355
    0
    So it will convert a linear Slope into a logarithmic slope?


    The sinewave,triangle,square waveform output is linear amplitudes , how can i make it Logarithmic amplitudes?

    Is logarithmic amplitude the same than as Damping?
     
  4. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    ~Think carefully about your questions.

    A sweep generator provides two outputs.
    One is a linear ramp and meant to drive the x axis of the display device (plotter, scope, digitiser etc) at a steady rate across the display.

    The second provides an output that varies in frequency, either in direct proportion or logarithmic proportion, to the ramp signal.

    The amplitude of this second ouput is designed to remain as constant as humanly possible otherwise the instrument would be of little value.
     
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