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6th order bessel filter

Started by tameze sylvianne March 10, 2003
Hello,

I'm a beginner in Matlab. I would like to program a
6th order bessel Low pass filter using matlab.
My specifications are as follow : Cutott frequency
8.2MHz and my sampling rate is 52.32 MHz (for DVD
purposes).
My Code is the following

clear all;
a=[10395];
wo=1/(8.2e6*2*pi)

b=[1*(wo^6) 21*(wo^5) 210*(wo^4) 1260*(wo^3)
4725*(wo^2) 10395*(wo) 10395];

c=tf(a,b)
h(c,1/52.32e6,'tustin')
bode(h)

I do not understand why on my plot,i do not read the
same cut off frequency of 8.2 MHZ that i entered in
the code. Instead, at -3dB i get 1.5e7.
Can someone please tell me what i am doing wrong?

Thanks

=====
Sylvianne Tameze
Sibeliuslaan 93d
5654 CV Eindhoven
The Netherlands
tel:040-2515881
tel:06-13105124



You might want to use this:

[b,a]sself(6,8.2e6);
w=0:100:15e6;
freqs(b,a,w);

cheers,
niranjan -
Hello,

I'm a beginner in Matlab. I would like to program a
6th order bessel Low pass filter using matlab.
My specifications are as follow : Cutott frequency
8.2MHz and my sampling rate is 52.32 MHz (for DVD
purposes).
My Code is the following

clear all;
a=[10395];
wo=1/(8.2e6*2*pi)

b=[1*(wo^6) 21*(wo^5) 210*(wo^4) 1260*(wo^3)
4725*(wo^2) 10395*(wo) 10395];

c=tf(a,b)
h(c,1/52.32e6,'tustin')
bode(h)

I do not understand why on my plot,i do not read the
same cut off frequency of 8.2 MHZ that i entered in
the code. Instead, at -3dB i get 1.5e7.
Can someone please tell me what i am doing wrong?

Thanks

=====
Sylvianne Tameze
Sibeliuslaan 93d
5654 CV Eindhoven
The Netherlands
tel:040-2515881
tel:06-13105124


Hi,
Did you try comparing your values with the 'besself'
function in signal processing toolbox?

Navan

--- tameze sylvianne <> wrote:
> Hello,
>
> I'm a beginner in Matlab. I would like to program a
> 6th order bessel Low pass filter using matlab.
> My specifications are as follow : Cutott frequency
> 8.2MHz and my sampling rate is 52.32 MHz (for DVD
> purposes).
> My Code is the following
>
> clear all;
> a=[10395];
> wo=1/(8.2e6*2*pi)
>
> b=[1*(wo^6) 21*(wo^5) 210*(wo^4) 1260*(wo^3)
> 4725*(wo^2) 10395*(wo) 10395];
>
> c=tf(a,b)
> h(c,1/52.32e6,'tustin')
> bode(h)
>
> I do not understand why on my plot,i do not read the
> same cut off frequency of 8.2 MHZ that i entered in
> the code. Instead, at -3dB i get 1.5e7.
> Can someone please tell me what i am doing wrong?
>
> Thanks


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