WSJT-X/fil659.f
Joe Taylor 068551448b Changes to compile on K1JT machine, Kubuntu 6.06.
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/map65@407 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
2007-06-23 15:03:19 +00:00

60 lines
1.9 KiB
Fortran

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