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89 lines
2.4 KiB
Fortran
89 lines
2.4 KiB
Fortran
subroutine ft2_gfsk_iwave(msg37,f0,snrdb,iwave)
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! Generate waveform for experimental "FT2" mode
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use packjt77
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include 'ft2_params.f90' !Set various constants
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parameter (NWAVE=(NN+2)*NSPS)
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character msg37*37,msgsent37*37
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real wave(NWAVE),xnoise(NWAVE)
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real dphi(NWAVE)
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real pulse(480)
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integer itone(NN)
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integer*2 iwave(NWAVE) !Generated full-length waveform
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logical first
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data first/.true./
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save pulse
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twopi=8.0*atan(1.0)
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fs=12000.0 !Sample rate (Hz)
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dt=1.0/fs !Sample interval (s)
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hmod=0.8 !Modulation index (MSK=0.5, FSK=1.0)
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tt=NSPS*dt !Duration of symbols (s)
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baud=1.0/tt !Keying rate (baud)
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bw=1.5*baud !Occupied bandwidth (Hz)
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txt=NZ*dt !Transmission length (s)
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bandwidth_ratio=2500.0/(fs/2.0)
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! sig=sqrt(2*bandwidth_ratio) * 10.0**(0.05*snrdb)
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! if(snrdb.gt.90.0) sig=1.0
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txt=NN*NSPS/12000.0
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if(first) then
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! The filtered frequency pulse
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do i=1,480
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tt=(i-240.5)/160.0
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pulse(i)=gfsk_pulse(1.0,tt)
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enddo
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dphi_peak=twopi*(hmod/2.0)/real(NSPS)
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first=.false.
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endif
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! Source-encode, then get itone():
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itype=1
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call genft2(msg37,0,msgsent37,itone,itype)
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! Create the instantaneous frequency waveform
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dphi=0.0
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do j=1,NN
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ib=(j-1)*160+1
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ie=ib+480-1
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dphi(ib:ie)=dphi(ib:ie)+dphi_peak*pulse*(2*itone(j)-1)
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enddo
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phi=0.0
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wave=0.0
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sqrt2=sqrt(2.)
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dphi=dphi+twopi*f0*dt
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do j=1,NWAVE
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wave(j)=sqrt2*sin(phi)
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sqsig=sqsig + wave(j)**2
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phi=mod(phi+dphi(j),twopi)
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enddo
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wave(1:160)=wave(1:160)*(1.0-cos(twopi*(/(i,i=0,159)/)/320.0) )/2.0
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wave(145*160+1:146*160)=wave(145*160+1:146*160)*(1.0+cos(twopi*(/(i,i=0,159)/)/320.0 ))/2.0
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wave(146*160+1:)=0.
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if(snrdb.gt.90.0) then
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iwave=nint((32767.0/sqrt(2.0))*wave)
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return
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endif
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sqnoise=1.e-30
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if(snrdb.lt.90) then
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do i=1,NWAVE !Add gaussian noise at specified SNR
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xnoise(i)=gran() !Noise has rms = 1.0
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enddo
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endif
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xnoise=xnoise*sqrt(0.5*fs/2500.0)
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fac=30.0
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snr_amplitude=10.0**(0.05*snrdb)
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wave=fac*(snr_amplitude*wave + xnoise)
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datpk=maxval(abs(wave))
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print*,'A',snr_amplitude,datpk
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iwave=nint((30000.0/datpk)*wave)
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return
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end subroutine ft2_gfsk_iwave
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