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https://github.com/saitohirga/WSJT-X.git
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60 lines
1.8 KiB
FortranFixed
60 lines
1.8 KiB
FortranFixed
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subroutine fil659(id,n1,f0,c2a,c2b,n2)
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C FIR lowpass filter designed using ScopeFIR
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C fsample (Hz) 96000.0 Input sample rate
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C Ntaps 23 Number of filter taps
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C fc (Hz) 1500 Cutoff frequency (-3 dB)
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C fstop (Hz) 12000 Lower limit of stopband
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C Ripple (dB) 0.05 Ripple in passband
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C Stop Atten (dB) 45 Stopband attenuation
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C fout (Hz) 24000.0 Output sample rate
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parameter (NTAPS=23)
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parameter (NH=NTAPS/2)
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parameter (NDOWN=4) !Downsample ratio = 1/4
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integer*2 id(4,n1)
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complex c2a(n1/NDOWN),c2b(n1/NDOWN)
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complex z
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real*8 dt,dpha,twopi
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complex w,w0,wstep
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data twopi/6.2831853071796/
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C Filter coefficients:
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real a(-NH:NH)
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data a/
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+ -0.006192694772,-0.009005098228,-0.011852791893,-0.011064464062,
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+ -0.004044201520, 0.010987986233, 0.034169891384, 0.063459565756,
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+ 0.094796253511, 0.122845919676, 0.142302928050, 0.149270332282,
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+ 0.142302928050, 0.122845919676, 0.094796253511, 0.063459565756,
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+ 0.034169891384, 0.010987986233,-0.004044201520,-0.011064464062,
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+ -0.011852791893,-0.009005098228,-0.006192694772/
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n2=(n1-NTAPS+NDOWN)/NDOWN
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k0=NH-NDOWN+1
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C Loop over all output samples
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dt=1.d0/96000.d0
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dpha=twopi*f0*dt
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wstep=cmplx(cos(dpha),sin(dpha))
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k=k0+NDOWN
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w0=1.0
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do i=1,n2
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c2a(i)=0.
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c2b(i)=0.
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k=k0 + NDOWN*i
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w=w0
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do j=-NH,NH
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w=w*wstep
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if(j.eq.3-NH) w0=w
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z=a(j)*cmplx(float(id(1,j+k)),float(id(2,j+k)))*w
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c2a(i)=c2a(i) + z
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z=a(j)*cmplx(float(id(3,j+k)),float(id(4,j+k)))*w
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c2b(i)=c2b(i) + z
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enddo
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enddo
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return
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end
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