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45 lines
1.4 KiB
Fortran
45 lines
1.4 KiB
Fortran
subroutine fil6521(c1,n1,c2,n2)
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! FIR lowpass filter designed using ScopeFIR
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! Pass #1 Pass #2
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!-----------------------------------------------
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! fsample (Hz) 1378.125 Input sample rate
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! Ntaps 21 Number of filter taps
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! fc (Hz) 40 Cutoff frequency
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! fstop (Hz) 172.266 Lower limit of stopband
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! Ripple (dB) 0.1 Ripple in passband
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! Stop Atten (dB) 38 Stopband attenuation
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! fout (Hz) 344.531 Output sample rate
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parameter (NTAPS=21)
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parameter (NH=(NTAPS-1)/2)
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parameter (NDOWN=4) !Downsample ratio = 1/4
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complex c1(n1)
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complex c2(n1/NDOWN)
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! Filter coefficients:
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real a(-NH:NH)
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data a/ &
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-0.011958606980,-0.013888627387,-0.015601306443,-0.010602249570, &
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0.003804023436, 0.028320058273, 0.060903935217, 0.096841904411, &
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0.129639871228, 0.152644580853, 0.160917511283, 0.152644580853, &
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0.129639871228, 0.096841904411, 0.060903935217, 0.028320058273, &
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0.003804023436,-0.010602249570,-0.015601306443,-0.013888627387, &
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-0.011958606980/
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n2=(n1-NTAPS+NDOWN)/NDOWN
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k0=NH-NDOWN+1
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! Loop over all output samples
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do i=1,n2
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c2(i)=0.
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k=k0 + NDOWN*i
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do j=-NH,NH
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c2(i)=c2(i) + c1(j+k)*a(j)
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enddo
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enddo
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return
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end subroutine fil6521
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