72 lines
1.6 KiB
Fortran
72 lines
1.6 KiB
Fortran
subroutine js8_downsample(dd,newdat,f0,c1)
|
|
|
|
! Downconvert to complex data sampled at 200 Hz ==> 32 samples/symbol
|
|
|
|
!include 'js8_params.f90'
|
|
|
|
parameter (NDFFT1=NSPS*NDD, NDFFT2=NDFFT1/NDOWN) ! Downconverted FFT Size - 192000/60 = 3200
|
|
parameter (NTAPER=1) ! Should we taper the downsample?
|
|
|
|
logical newdat,first
|
|
|
|
complex c1(0:NDFFT2-1)
|
|
complex cx(0:NDFFT1/2)
|
|
real dd(NMAX),x(NDFFT1),taper(0:NDD)
|
|
equivalence (x,cx)
|
|
data first/.true./
|
|
save cx,first,taper
|
|
|
|
if(first) then
|
|
pi=4.0*atan(1.0)
|
|
do i=0,NDD
|
|
taper(i)=0.5*(1.0+cos(i*pi/NDD))
|
|
enddo
|
|
first=.false.
|
|
endif
|
|
|
|
if(newdat) then
|
|
if(NWRITELOG.eq.1) then
|
|
write(*,*) '<DecodeDebug> newdat', NMAX, NDFFT1
|
|
flush(6)
|
|
endif
|
|
|
|
! Data in dd have changed, recompute the long FFT
|
|
x(1:NMAX)=dd
|
|
x(NMAX+1:NDFFT1)=0. !Zero-pad the x array
|
|
call four2a(cx,NDFFT1,1,-1,0) !r2c FFT to freq domain
|
|
newdat=.false.
|
|
endif
|
|
|
|
df=12000.0/NDFFT1
|
|
baud=12000.0/NSPS
|
|
i0=nint(f0/df)
|
|
ft=f0+8.5*baud
|
|
it=min(nint(ft/df),NDFFT1/2)
|
|
fb=f0-1.5*baud
|
|
ib=max(1,nint(fb/df))
|
|
k=0
|
|
c1=0.
|
|
|
|
if(NWRITELOG.eq.1) then
|
|
write(*,*) '<DecodeDebug> ds', df, baud, i0, ib, it
|
|
flush(6)
|
|
endif
|
|
|
|
do i=ib,it
|
|
c1(k)=cx(i)
|
|
k=k+1
|
|
enddo
|
|
|
|
if(NTAPER.eq.1) then
|
|
c1(0:NDD)=c1(0:NDD)*taper(NDD:0:-1)
|
|
c1(k-1-NDD:k-1)=c1(k-1-NDD:k-1)*taper
|
|
endif
|
|
|
|
c1=cshift(c1,i0-ib)
|
|
call four2a(c1,NDFFT2,1,1,1) !c2c FFT back to time domain
|
|
fac=1.0/sqrt(float(NDFFT1)*NDFFT2)
|
|
c1=fac*c1
|
|
|
|
return
|
|
end subroutine js8_downsample
|