Active band pass filter.

[shomikc]

Hi everyone. I want to make an active band pass filter that will receive a signal which is broadcast at 800 kHz center frequency and a certain bandwidth.. At the same time I want the filter to reject a signal that is broadcast at 600 kHz and a bandwidth of 100 kHz and reject another signal broadcast at 1 MHz with bandwidth of 100 kHz.

So my question is should the bandwidth of the signal of the broadcast at 800 kHz will be 650 kHz to 950 kHz.

 

[BradtheRad]

Consider that the two filters do not necessarily have to be placed in series. They might be in parallel.
Try experimenting with simple LC arrangements. An inductor & capacitor create a resonant frequency. You can put the LC in series or in parallel. You can: (a) divert signal to ground through an LC arrangement, or (b) pass signal along through an LC arrangement.

 

[KlausST]

Hi,

usually it´s the other way round:
* You determine the bandwidth you need. (@800kHz)
* and how much you want to attenuate the other frequencies.

Klaus

 

[danadakk]

Simple 2 stage, 2 second order sections, cascade of LPF anf HPF ?

How much rejection you want for the out of band principal components ?


Regards, Dana.

--- Updated Apr 12, 2022 ---

Fooling around with a designer uitilty this is close, and you might be able to adjust the
notches to suppress the two frweqs you want to suppress.

RF Tools | LC Filter Design Tool

Regards, Dana.

--- Updated Apr 12, 2022 ---

You would play with the order of the filter and / or BW of the primary 800 Khz.

You would have to do a T and component tolerance analysis / sim to insure it
meets your specs. Or if a one off tune it by changing its component values


Regards, Dana..

 

[shomikc]

Simple 2 stage, 2 second order sections, cascade of LPF anf HPF ?

How much rejection you want for the out of band principal components ?


Regards, Dana.

--- Updated Apr 12, 2022 ---

Fooling around with a designer uitilty this is close, and you might be able to adjust the
notches to suppress the two frweqs you want to suppress.

RF Tools | LC Filter Design Tool

View attachment 175389

View attachment 175388


Regards, Dana.

--- Updated Apr 12, 2022 ---

You would play with the order of the filter and / or BW of the primary 800 Khz.

You would have to do a T and component tolerance analysis / sim to insure it
meets your specs. Or if a one off tune it by changing its component values


Regards, Dana..

It is a cascade of HPF and LPF and the center frequency of 800 kHz.

 

[crutschow]

Can't do the design without knowing how much rejection you need for the out-of-band frequencies.

 

[LvW]

Hi everyone. I want to make an active band pass filter that will receive a signal which is broadcast at 800 kHz center frequency and a certain bandwidth.. At the same time I want the filter to reject a signal that is broadcast at 600 kHz and a bandwidth of 100 kHz and reject another signal broadcast at 1 MHz with bandwidth of 100 kHz.

So my question is should the bandwidth of the signal of the broadcast at 800 kHz will be 650 kHz to 950 kHz.

What do you mean with "reject"? A bandpass can only attenuate unwanted frequecies.
However - theoretically - it is possible to completely suppress one single out-of-band frequency.

 

[FvM]

Post #5 is suggesting first order high and low pass filters. Did you calculate achievable filter transfer functions with this filter type or is it just a shoot in the dark?

 

[danadakk]

shomikc, you still need to answer the most basic of questions regarding filters :

1) Spec for out of band rejection ?
2) Linear phase solution needed ?
3) Input output impedance requirements ?
4) G thru filter ?
5) Allowed passband ripple ?
6) Noise considerations ?
7) What is the application, why is filter needed ? Answer may reveal other possible
solutions.

Regards, Dana.