mirror of https://github.com/pavel-demin/ft8d.git
55 lines
1.6 KiB
Fortran
55 lines
1.6 KiB
Fortran
subroutine sync8d(cd0,i0,ctwk,itwk,sync)
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! Compute sync power for a complex, downsampled FT8 signal.
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parameter(NP2=2812,NDOWN=20)
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complex cd0(0:3199)
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complex csync(0:6,32)
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complex csync2(32)
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complex ctwk(32)
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complex z1,z2,z3
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logical first
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integer icos7(0:6)
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data icos7/3,1,4,0,6,5,2/
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data first/.true./
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save first,twopi,fs2,dt2,taus,baud,csync
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p(z1)=real(z1)**2 + aimag(z1)**2 !Statement function for power
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! Set some constants and compute the csync array.
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if( first ) then
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twopi=8.0*atan(1.0)
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fs2=4000.0/NDOWN !Sample rate after downsampling
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dt2=1/fs2 !Corresponding sample interval
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taus=32*dt2 !Symbol duration
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baud=1.0/taus !Keying rate
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do i=0,6
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phi=0.0
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dphi=twopi*icos7(i)*baud*dt2
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do j=1,32
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csync(i,j)=cmplx(cos(phi),sin(phi)) !Waveform for 7x7 Costas array
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phi=mod(phi+dphi,twopi)
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enddo
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enddo
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first=.false.
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endif
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sync=0
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do i=0,6 !Sum over 7 Costas frequencies and
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i1=i0+i*32 !three Costas arrays
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i2=i1+36*32
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i3=i1+72*32
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csync2=csync(i,1:32)
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if(itwk.eq.1) csync2=ctwk*csync2 !Tweak the frequency
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z1=0.
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z2=0.
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z3=0.
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if(i1.ge.0 .and. i1+31.le.NP2-1) z1=sum(cd0(i1:i1+31)*conjg(csync2))
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if(i2.ge.0 .and. i2+31.le.NP2-1) z2=sum(cd0(i2:i2+31)*conjg(csync2))
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if(i3.ge.0 .and. i3+31.le.NP2-1) z3=sum(cd0(i3:i3+31)*conjg(csync2))
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sync = sync + p(z1) + p(z2) + p(z3)
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enddo
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return
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end subroutine sync8d
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