WSJT-X/fil652.f

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subroutine fil652(c1,n1,c2,n2)
C FIR lowpass filter designed using ScopeFIR
C fsample = 2756.25 Hz
C Ntaps = 31
C fc = 500 Hz
C fstop = 689.0625 Hz
C Ripple = 0.5 dB
C Stop Atten = 50 dB
C fout = 1378.125 Hz
parameter (NTAPS=31)
parameter (NH=NTAPS/2)
parameter (NDOWN=2) !Downsample ratio
complex c1(n1)
complex c2(n2)
C Filter coefficients:
real a(-NH:NH)
data a/
+ -0.000859869246,-0.008518289484,-0.011250152625,-0.001061705256,
+ 0.013958392156, 0.010047338728,-0.015003870003,-0.025027880982,
+ 0.007151700557, 0.043634723913, 0.016788108012,-0.061886192062,
+ -0.073548459520, 0.075261027466, 0.306638863577, 0.419826269508,
+ 0.306638863577, 0.075261027466,-0.073548459520,-0.061886192062,
+ 0.016788108012, 0.043634723913, 0.007151700557,-0.025027880982,
+ -0.015003870003, 0.010047338728, 0.013958392156,-0.001061705256,
+ -0.011250152625,-0.008518289484,-0.000859869246/
n2=(n1-NTAPS+NDOWN)/NDOWN
k0=NH-NDOWN+1
C Loop over all output samples
do i=1,n2
c2(i)=0.
k=k0 + NDOWN*i
do j=-NH,NH
c2(i)=c2(i) + c1(j+k)*a(j)
enddo
enddo
return
end