bode plot

Discussion in 'Homework Help' started by full, Dec 11, 2014.

  1. full

    Thread Starter Member

    May 3, 2014
    225
    2
    hello everyone
    I did problem from bode plot
    please see my solution true?
    a.PNG
     
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  2. full

    Thread Starter Member

    May 3, 2014
    225
    2
    Last edited: Dec 12, 2014
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Here is what LTSpice shows:

    240l.gif

    Look familiar?
     
    Last edited: Dec 11, 2014
  4. full

    Thread Starter Member

    May 3, 2014
    225
    2
  5. full

    Thread Starter Member

    May 3, 2014
    225
    2
    I did in alpha the answer is different from you
    if you are see from 0.1 your start from 20 dB and in alpha from 0.1 start at 5.1dB

    Capture.PNG
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Begs the question: Is one in Hz and the other in radians?
     
  7. MrAl

    Well-Known Member

    Jun 17, 2014
    2,418
    488
    Hello there,

    Mike:
    You probably want to check your Laplace function in post #3 because that seems to yield the wrong result. I'll double check this too. It could be that LTSpice leaves out the constant gain in the Laplace function.
    CHECKED:
    Ok, it's just that LTSpice uses frequency in Hertz instead of angular frequency w. If we plot from 0.01/2/pi to 100/2/pi and for x=f*2*pi we get the same plot as post #2 for the amplitude.

    Full:
    The amplitude function is:
    |V|=(30*w*sqrt(w^2+100)*sqrt(w^2+144))/(sqrt(w^2+64)*sqrt(w^4+71*w^2+625))

    and so the amplitude in db is:
    Vdb=20*log10(|V|)

    You can use that to check your results, but the plot comes out the same as your plot in post #2.
    The x axis variable is 'w' not 'f in Hertz' just to clear that up, and w=2*pi*f.

    Again you are probably just overlooking something simple. It's hard to read your sheets though because the writing is so faint.
     
    Last edited: Dec 12, 2014
    full likes this.
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