WSJT-X/fil653.f

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subroutine fil653(c1,n1,c2,n2)
C FIR lowpass filter designed using ScopeFIR
C fsample = 1378.125 Hz
C Ntaps = 45
C fc = 100 Hz
C fstop = 172.265625 Hz
C Ripple = 0.5 dB
C Stop Atten = 50 dB
C fout = 172.265625 Hz
C BW = 200 Hz
parameter (NTAPS=45)
parameter (NH=NTAPS/2)
parameter (NDOWN=4) !Downsample ratio
complex c1(n1)
complex c2(n2)
C Filter coefficients:
real a(-NH:NH)
data a/
+ -0.000005569862,-0.002503777832,-0.004040335617,-0.005717910288,
+ -0.006153385485,-0.004446125293,-0.000305215272, 0.005557289511,
+ 0.011329120672, 0.014496551280, 0.012703875898, 0.004837591829,
+ -0.008060363689,-0.022474422302,-0.032964876083,-0.033575486327,
+ -0.019743889907, 0.009895672340, 0.052467109908, 0.101031155027,
+ 0.146073001698, 0.177927966814, 0.189427119395, 0.177927966814,
+ 0.146073001698, 0.101031155027, 0.052467109908, 0.009895672340,
+ -0.019743889907,-0.033575486327,-0.032964876083,-0.022474422302,
+ -0.008060363689, 0.004837591829, 0.012703875898, 0.014496551280,
+ 0.011329120672, 0.005557289511,-0.000305215272,-0.004446125293,
+ -0.006153385485,-0.005717910288,-0.004040335617,-0.002503777832,
+ -0.000005569862/
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