How to get the -3dB Frequency value for a semilog plot ?

Question

GEOFFREY LECOQ 2021-3-17

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/776152-how-to-get-the-3db-frequency-value-for-a-semilog-plot

回答： Pavan Guntha 2021-3-23

MATLAB_BJioUJf2OK.png

Hi,

I try to add a line on my graph on -3dB for my Bode Graph, i use a table for store all of my data like Frequency, Gain, Ouput voltage, Input voltage. I already make the semi-log plot but i don't know how get the value.

First of all i try to make a line and find the intersection but i don't understand how i can't use it.

I think i need to make an linear regression of my table to solve the equation "f(x)=-3", i'm not sure.

Thanks !

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Pavan Guntha 2021-3-23

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/776152-how-to-get-the-3db-frequency-value-for-a-semilog-plot#answer_655602

在 MATLAB Online 中打开

You may have to first find the index at which the gain is -3 dB (i.e., in Classeurl.g). Then the frequency can be found by calculating the value of Classeurl.f at that index. The following code illustrates the idea:

index = Classeurl.g == -3;  
f_3dB = Classeurl.f(index);
% To plot a vertical line at -3 dB frequency:
semilogx(x,y,'-')  
hold on  
xline(f_3dB)  
hold off