WSJT-X/fil651.f

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subroutine fil651(d,n1,c,n2)
C FIR lowpass mixing filter designed with ScopeFIR. Real in, complex out.
C fsample = 5512.5 Hz
C Ntaps = 31
C fc = 1000 Hz
C fstop = 1378.125 Hz
C Ripple = 0.5 dB
C Stop Atten = 50 dB
C fmix = 1378.125 Hz
C fout = 2706.25 Hz
parameter (NTAPS=31)
parameter (NH=NTAPS/2)
parameter (NDOWN=2) !Downsample ratio
real d(n1)
complex c(*)
complex ck(-NH:NH)
data ck/
+ (-0.000000073578,-0.000859869243),
+ ( 0.008518289457,-0.000000680308),
+ ( 0.000000834309, 0.011250152594),
+ (-0.001061705254, 0.000000072679),
+ ( 0.000000875897, 0.013958392128),
+ (-0.010047338711, 0.000000573160),
+ ( 0.000000770320, 0.015003869984),
+ (-0.025027880956, 0.000001142192),
+ ( 0.000000285583, 0.007151700551),
+ (-0.043634723888, 0.000001493512),
+ (-0.000000478847,-0.016788108005),
+ (-0.061886192046, 0.000001412144),
+ (-0.000001258694,-0.073548459509),
+ (-0.075261027462, 0.000000858668),
+ (-0.000001749252,-0.306638863572),
+ ( 0.419826269508, 0.000000000000),
+ (-0.000001749252, 0.306638863572),
+ (-0.075261027462,-0.000000858668),
+ (-0.000001258694, 0.073548459509),
+ (-0.061886192046,-0.000001412144),
+ (-0.000000478847, 0.016788108005),
+ (-0.043634723888,-0.000001493512),
+ ( 0.000000285583,-0.007151700551),
+ (-0.025027880956,-0.000001142192),
+ ( 0.000000770320,-0.015003869984),
+ (-0.010047338711,-0.000000573160),
+ ( 0.000000875897,-0.013958392128),
+ (-0.001061705254,-0.000000072679),
+ ( 0.000000834309,-0.011250152594),
+ ( 0.008518289457, 0.000000680308),
+ (-0.000000073578, 0.000859869243)/
n2=(n1-NTAPS+NDOWN)/NDOWN
k0=NH-NDOWN+1
do i=1,n2
c(i)=0.
k=k0 + NDOWN*i
do j=-NH,NH
c(i)=c(i) + d(j+k)*conjg(ck(j))
enddo
enddo
return
end