WSJT-X/lpf1.f

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subroutine lpf1(dat,jz,nz,mousedf,mousedf2)
parameter (NMAX=1024*1024)
parameter (NMAXH=NMAX)
real dat(jz),x(NMAX)
complex c(0:NMAXH)
equivalence (x,c)
C Find FFT length
xn=log(float(jz))/log(2.0)
n=xn
if((xn-n).gt.0.) n=n+1
nfft=2**n
nh=nfft/2
C Load data into real array x; pad with zeros up to nfft.
do i=1,jz
x(i)=dat(i)
enddo
if(nfft.gt.jz) call zero(x(jz+1),nfft-jz)
C Do the FFT
call xfft(x,nfft)
df=11025.0/nfft
ia=70/df
do i=0,ia
c(i)=0.
enddo
ia=5000.0/df
do i=ia,nh
c(i)=0.
enddo
C See if frequency needs to be shifted:
ndf=0
if(mousedf.lt.-600) ndf=-670
if(mousedf.gt.600) ndf=1000
if(mousedf.gt.1600) ndf=2000
if(mousedf.gt.2600) ndf=3000
if(ndf.ne.0) then
C Shift frequency up or down by ndf Hz:
i0=nint(ndf/df)
if(i0.lt.0) then
do i=nh,-i0,-1
c(i)=c(i+i0)
enddo
do i=0,-i0-1
c(i)=0.
enddo
else
do i=0,nh-i0
c(i)=c(i+i0)
enddo
endif
endif
mousedf2=mousedf-ndf !Adjust mousedf
call four2a(c,nh,1,1,-1) !Return to time domain
fac=1.0/nfft
nz=jz/2
do i=1,nz
dat(i)=fac*x(i)
enddo
return
end