WSJT-X/lib/fsk4hf/watterson.f90

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Fortran
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subroutine watterson(c,npts,fs,delay,fspread)
include 'wsprlf_params.f90'
complex c(0:npts-1)
complex c2(0:NZMAX-1)
complex cs1(0:NZMAX-1)
complex cs2(0:NZMAX-1)
nonzero=0
df=fs/npts
if(fspread.gt.0.0) then
do i=0,npts-1
xx=gran()
yy=gran()
cs1(i)=0.707*cmplx(xx,yy)
xx=gran()
yy=gran()
cs2(i)=0.707*cmplx(xx,yy)
enddo
call four2a(cs1,npts,1,-1,1) !To freq domain
call four2a(cs2,npts,1,-1,1)
do i=0,npts-1
f=i*df
if(i.gt.npts/2) f=(i-npts)*df
x=(f/(0.5*fspread))**2
a=0.
if(x.le.50.0) then
a=exp(-x)
endif
cs1(i)=a*cs1(i)
cs2(i)=a*cs2(i)
if(abs(f).lt.10.0) then
p1=real(cs1(i))**2 + aimag(cs1(i))**2
p2=real(cs2(i))**2 + aimag(cs2(i))**2
if(p1.gt.0.0) nonzero=nonzero+1
! write(62,3101) f,p1,p2,db(p1+1.e-12)-60,db(p2+1.e-12)-60
!3101 format(f10.3,2f12.3,2f10.3)
endif
enddo
call four2a(cs1,npts,1,1,1) !Back to time domain
call four2a(cs2,npts,1,1,1)
cs1(0:npts-1)=cs1(0:npts-1)/npts
cs2(0:npts-1)=cs2(0:npts-1)/npts
endif
nshift=nint(0.001*delay*fs)
c2(0:npts-1)=cshift(c(0:npts-1),nshift)
sq=0.
do i=0,npts-1
if(nonzero.gt.1) then
c(i)=0.5*(cs1(i)*c(i) + cs2(i)*c2(i))
else
c(i)=0.5*(c(i) + c2(i))
endif
sq=sq + real(c(i))**2 + aimag(c(i))**2
! write(61,3001) i/12000.0,c(i)
!3001 format(3f12.6)
enddo
rms=sqrt(sq/npts)
c=c/rms
return
end subroutine watterson