Low pass filter cut off frequency

[Dr. Dhiman Kakati]

Hi all, i am designing a receiver for detection of MSK signal but i need to be clear about the low pass filter cut off frequency, can any one tell me mathematical relation between bit rate and cut off frequency as I need to set it in the LPF component parameter, or is it vary with modulation technique?
I would like to know the same for band pass filter also. ie, how much bandwidth i should set.
I want to know it in mathematical form so that it is easily understandable.

I want to give the cut off frequency in script form at the low pass filter component property.

Thanks in advance,

With regards

[alistu]

Hi Dhiman,

As far as I know, it is only the Shannon theory that relates bit rate and bandwidth by C=B*log(1+S/N) to estimate the channel capacity. Even though I have searched for it, I haven’t found any relationship between these two, except for some experimental relations like the ones in Optisystem samples in script mode.

I always watch the symbols in constellation visualizer before making the relation in the script to see if the symbols are drawn to the origin. If they are, then some frequencies the symbols are becoming zero (due to being filtered) and it shows that my allocated bandwidth is not enough and it is eliminating some symbols, so I have to increase it.

[Dr. Dhiman Kakati]

Thanks Alistu for the reply. Still I am not finding the answer I am looking for. I am also searching for the same.

[Dhananjay Patel]

Dear dhiman,

kindly refer to some good books on RF microwave filters from your college library.

I also agree with what alitsu has said. I also do the same iterative process in order to get good constalletion. Vary the cut off frequency and see the best possible outputs available.

Also you need to check, what spectrum do u exactly need after filtering (I am the maximum or minimum frequency at the output filter) So accordingly you can decide the cut off frequency of the same

[Dr. Dhiman Kakati]

Thanks a lot, Dhananjay.

Regards

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