[scilab-Users] 3D plot of Butterworth polynomial?

[Pedro Ledoux]

Among free softwares the circuit simulator Qucs has a very good toolbox 
to project filters. In it you chose the kind of filter(chebyshev, 
butterwoth, cauer etc), the cutting frequencies, gain etc and it will 
give you a schematic of a filter which fit those specifications.If you 
use Linux, in Ubuntu and Fedora you can find the Qucs easily in it's 
respective pack manegers.

http://qucs.sourceforge.net/

Several months ago I had to project some filtres. I've chose do it using only free softwares. I had to project Active and passive filters. I coul do it sucessfoully with Scilab. One of those filters was a Butterworth. The scilab poly function was exelent to do it. 

Well. A good way to project an ACTIVE Butterworth Filter using Scilab was project first the equivalent low-pass filter. So you use: s=poly(0,'s'), with s you wright the thansfer function ex: p=1/((s+1)*(s+3)). If your filter is not a low pass you should use the frequency transform. For example, to high pass filter you should type after it:z=poly(0,'z'); s=2*%pi*450000/z; p and now the scilab will show the polynomial function after the frequency transformation. With scilab's bode ploting function you can see the bode diagram for this function.

For passive filters I used another procedure.



I'm sending my script file which I used in my project of a high pass Chevychev filter. In a Butterworth one only the polynomial chances.

--- Em ter, 9/11/10, hadi motamedi <motamedi24 at gmail.com> escreveu:

De: hadi motamedi <motamedi24 at gmail.com>
Assunto: Re: [scilab-Users] 3D plot of Butterworth polynomial?
Para: users at lists.scilab.org
Data: Terça-feira, 9 de Novembro de 2010, 3:18

On 11/7/10, Ronald Michaels <ron at phenotypescreening.com> wrote:
> Hi -
>
> Assuming that you want a circular filter:
>
> Take the first equation in your link below and set a and b to 1.  Then
> set the origin of the x,y axis system to the center of your image, i.e.
> x = 0 and y = 0 at center of image.  Calculate r for each x,y pixel
> location.  Then use r in the second equation in link to find the value
> of the filter for that x,y location.  Find the equivalent position in
> image coordinates (u,v) and place filter value there in Filter array.
>
> Ron
>
>
Thank you very much for your help. Sorry do you know a free software
application that lets me to write complex mathematical expressions? It
seems that I didn't describe my case exactly so I need to write the
expression by my own and then ask you what I need to do with obtaining
such a 2-D filter?



      
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