WSJT-X/lib/genjtms3a.f90

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subroutine genjtms3a(chansym,nsym,iwave,nwave)
integer*1 chansym(nsym)
integer*2 iwave(30*48000)
real x(0:6191),x2(0:6191)
complex c(0:3096),c2(0:6191) !Could be 0:3096 ???
equivalence (x,c),(x2,c2)
do j=1,nsym !Define the baseband signal
i0=24*(j-1) !24 samples per symbol
x(i0:i0+23)=2*chansym(j)-1
enddo
nfft=24*nsym
fac=1.0/nfft
x(0:nfft-1)=fac*x(0:nfft-1)
call four2a(x,nfft,1,-1,0) !Forward r2c FFT
! Apply lowpass filter
fc=1200.0
bw=200.0
df=48000.0/nfft
nh=nfft/2
c2=0.
ib=2000.0/df
do i=0,ib
f=i*df
g=1.0
if(f.gt.fc) then
xx=(f-fc)/bw
g=exp(-xx*xx)
endif
c2(i)=g*c(i)
enddo
call four2a(c2,nfft,1,1,-1) !Inverse c2r FFT
nf0=nint(1500.0/df)
f0=nf0*df
twopi=8.0*atan(1.0)
dphi=twopi*f0/48000.0
phi=0.
peak=0.
sq=0.
do i=0,nfft-1
phi=phi+dphi
if(phi.gt.twopi) phi=phi-twopi
y=cos(phi)
x2(i)=y*x2(i)
sq=sq + x2(i)**2
if(abs(x2(i)).gt.peak) peak=abs(x2(i))
enddo
rms=sqrt(sq/nfft)
! print*,rms,peak,peak/rms
fac=32767.0/peak
do i=0,nfft-1
iwave(i+1)=fac*x2(i)
enddo
nwave=30*48000
nrpt=nwave/nfft
do n=2,nrpt
ib=n*nfft
ia=ib-nfft+1
iwave(ia:ib)=iwave(1:nfft)
enddo
return
end subroutine genjtms3a