WSJT-X/lib/ft2/ft2_iwave.f90

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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