WSJT-X/lib/ft8/foxfilt.f90

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subroutine foxfilt(nslots,width,wave)
parameter (NN=79,ND=58,KK=87,NSPS=4*1920)
parameter (NWAVE=NN*NSPS,NFFT=614400,NH=NFFT/2)
real wave(NWAVE)
real x(NFFT)
complex cx(0:NH)
equivalence (x,cx)
x(1:NWAVE)=wave
x(NWAVE+1:)=0.
call four2a(x,NFFT,1,-1,0) !r2c
df=48000.0/NFFT
fa=1800.0 - 0.5*6.25
fb=1800.0 + 7.5*6.25 + (nslots-1)*60.0
ia2=nint(fa/df)
ib1=nint(fb/df)
ia1=nint(ia2-width/df)
ib2=nint(ib1+width/df)
pi=4.0*atan(1.0)
do i=ia1,ia2
fil=(1.0 + cos(pi*df*(i-ia2)/width))/2.0
cx(i)=fil*cx(i)
enddo
do i=ib1,ib2
fil=(1.0 + cos(pi*df*(i-ib1)/width))/2.0
cx(i)=fil*cx(i)
enddo
cx(0:ia1-1)=0.
cx(ib2+1:)=0.
call four2a(cx,nfft,1,1,-1) !c2r
wave=x(1:NWAVE)/nfft
return
end subroutine foxfilt