How to decide the Band Pass filter Frequency range

Hi all,
I have one time domain signal, on which I have to apply the band pass filter. How can I decide the Band Pass Frequency range?
I am calculating the power of signal and plotting it on MATLAB i.e. frequency response. I am searching the frequency points, where the power has it's maximum value.
Is it the right way to search band pass filter frequency range?

The [ h, f ] = freqz(); function, returns magnitude (h) and frequency (f).
plot(f,20*log10(abs(h))). It plots the Power vs.. frequency.
But the problem is that it does not give the correct frequency value, where the power is maximum.
Any comment will be appreciated.

Regards,
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