1
$\begingroup$

I have an array of transfer functions and plotted multiple Bode plot. Now I need to add a horizontal line to show where all these Bode plots attain a gain of -8db. I know that previously people replied similar type of questions for drawing vertical line. But it seems that the same method is not working for horizontal lines? I also tried to draw a separate line and then used Show with the Bode plot diagram. But it didn't work. To summarise, what I am looking for is shown in this image. enter image description here - I am trying to draw the black lines and mark the intersection points with different marker colours. Could somebody help please?

$\endgroup$
0

2 Answers 2

2
$\begingroup$

This is a LogLinearPlot. Let's use an example plot from the documentation and draw lines over it.

Ra[f_] := (
 12200^2 f^4)/((f^2 + 
    20.6^2) Sqrt[(f^2 + 107.7^2) (f^2 + 737.9^2)] (f^2 + 12200^2))

LogLinearPlot[Ra[f], {f, 10, 10^5}, GridLines -> Automatic
 , Epilog -> {
   {Thick, Black, Line[{{Log[1000], 0}, {Log[1000], Ra[10^3]}}]}
   , {Thick, Red, Line[{{Log[10^1], Ra[10^3]}, {Log[1000], Ra[10^3]}}]}
   , {AbsolutePointSize[8], Darker@Green, Point[{Log[1000], Ra[10^3]}]}
   }
 ]

enter image description here

If you have a more specific question, you can update your post and present a minimal example featuring copy-paste-able Mathematica code.

$\endgroup$
1
  • $\begingroup$ Hi Syed, Thank you so much. Here is the transfer function: TF = TransferFunctionModel[{{{ 1.8831584343714116*^9 + 91654.79372668632 s}}, 2.3314280115350676*^9 + 134019.32322803652` s + 1. s^2}, s]. I would like to have the green point at your example at (34453.1, -8.5193} and draw the black and red lines in your example from that point. $\endgroup$
    – km3
    May 11, 2022 at 18:57
2
$\begingroup$

Use the GridLines option, and Mesh also if needed.

tfm = TransferFunctionModel[{{{1.8831584343714116*^9 + 91654.79372668632 s}}, 
    2.3314280115350676*^9 + 134019.32322803652` s + 1. s^2}, s];
pt = 10^5; 

BodePlot[tfm, PlotLayout -> "Magnitude", Mesh -> {{pt}}, 
    MeshStyle -> Directive[PointSize[Large], Green], 
    GridLines -> {{pt}, {20 Log10@Abs[tfm[I pt]][[1, 1]]}}, 
    GridLinesStyle -> {Directive[Black, Thick], Directive[Red, Thick]}]

enter image description here

$\endgroup$
1
  • 1
    $\begingroup$ Dear Suba, thank you so much. Really appreciate. $\endgroup$
    – km3
    May 19, 2022 at 15:19

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.