# Bode Plot Homework Help Please

Discussion in 'Homework Help' started by testing12, Oct 2, 2011.

1. ### testing12 Thread Starter Member

Jan 30, 2011
80
2
Hello Everyone,
Thanks to all of those who have helped me in the past, this forum has been fantastic, in particular special thanks to t.n.k.

Now, im trying to construct a Bode plot, however there are some descrepancies with the solutions. See below. Notice how my plot(graph paper) goes up to -20 db before going flat where as the solution does not quite get to -20. Can anyone tell me what im doing wrong? Im having some difficulty, i thought the place where the plot should stop increasing is when w = log 10 rad/s.
Best Regards.
Matt

Last edited: Oct 2, 2011

Jan 30, 2011
80
2

3. ### Zazoo Member

Jul 27, 2011
114
43
The plot in the solution is draw to be a better approximation of the actual magnitude curve. It looks like they used the actual magnitudes at the corner frequencies (instead of the magnitudes from the asymptotic plots you used in your solution.)

With three poles that close together, the magnitude in that region will be depressed by an amout close to 9dB (3dB per pole), i.e. closer to -30dB (vs. -20dB) at ω = 10.

4. ### testing12 Thread Starter Member

Jan 30, 2011
80
2
thank you. I reviewed other examples, i think my answer is a "close enough" approximation.