I use alpha ,but the answer is different from my : why? http://www.wolframalpha.com/input/?i=bode plot ((30s^3+660s^2+3600s)/(s^3+19s^2+113s+200))
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
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.