WSJT-X/lib/ft2/ft2_iwave.f90

subroutine ft2_iwave(msg37,f0,snrdb,iwave)

! Generate waveform for experimental "FT2" mode 

  use packjt77
  include 'ft2_params.f90'               !Set various constants
  parameter (NWAVE=NN*NSPS)
  character msg37*37,msgsent37*37
  real wave(NWAVE),xnoise(NWAVE)
  integer itone(NN)
  integer*2 iwave(NWAVE)                 !Generated full-length waveform
  
  twopi=8.0*atan(1.0)
  fs=12000.0                             !Sample rate (Hz)
  dt=1.0/fs                              !Sample interval (s)
  hmod=0.8                               !Modulation index (MSK=0.5, FSK=1.0)
  tt=NSPS*dt                             !Duration of symbols (s)
  baud=1.0/tt                            !Keying rate (baud)
  bw=1.5*baud                            !Occupied bandwidth (Hz)
  txt=NZ*dt                              !Transmission length (s)
  bandwidth_ratio=2500.0/(fs/2.0)
!  sig=sqrt(2*bandwidth_ratio) * 10.0**(0.05*snrdb)
!  if(snrdb.gt.90.0) sig=1.0
  txt=NN*NSPS/12000.0

! Source-encode, then get itone():
  itype=1
  call genft2(msg37,0,msgsent37,itone,itype)

  k=0
  phi=0.0 
  sqsig=0.
  do j=1,NN                             !Generate real waveform
     dphi=twopi*(f0*dt+(hmod/2.0)*(2*itone(j)-1)/real(NSPS))
     do i=1,NSPS
        k=k+1
        wave(k)=sqrt(2.0)*sin(phi)      !Signal has rms = 1.0
        sqsig=sqsig + wave(k)**2
        phi=mod(phi+dphi,twopi)
     enddo
  enddo

  if(snrdb.gt.90.0) then
     iwave=nint((32767.0/sqrt(2.0))*wave)
     return
  endif
  
  sqnoise=1.e-30
  if(snrdb.lt.90) then
     do i=1,NWAVE                   !Add gaussian noise at specified SNR
        xnoise(i)=gran()            !Noise has rms = 1.0
     enddo
  endif
  xnoise=xnoise*sqrt(0.5*fs/2500.0)
  fac=30.0
  snr_amplitude=10.0**(0.05*snrdb)
  wave=fac*(snr_amplitude*wave + xnoise)
  datpk=maxval(abs(wave))
  print*,'A',snr_amplitude,datpk

  iwave=nint((30000.0/datpk)*wave)
  
  return
end subroutine ft2_iwave