# Band stop filter

Discussion in 'General Electronics Chat' started by BOB?, Feb 4, 2008.

1. ### BOB? Thread Starter New Member

Feb 4, 2008
1
0
First I want to apologize for my bad English
On the forum I have found some information about the band-stop filter.
But the formulas are
R1=R2=2(R3)
C2 = C3 = 0,5(C1)
Fnotch = 1/ (4*PI*R3*C3)

My problem is that in my scheme R1 <> R2 and C2<>C3
Now my question is, does anybody now how I can calculate my Fnotch.

File size:
36.1 KB
Views:
75
2. ### Papabravo Expert

Feb 24, 2006
12,212
2,697
Well you have a low pass filter in parallel with a high pass filter. You can write an expression for the complex impedance of each filter and then combine the two impedances as (Z1*Z2)/(Z1 + Z2). Take the derivative with respect to frequency and solve for zero. That will give you the frequency where the impedance is a minimum. That is the bottom of the notch.

3. ### JoeJester AAC Fanatic!

Apr 26, 2005
4,073
1,774
It looks like you have a twin-t notch filter arrangement, however, your schematic doesn't show the proper values for the components of a twin-t notch.