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For now, change to BT=1.5 for FT8. This commit enables the waterfall analysis window. This decreases sidelobes significantly in exchange for increased noise bandwidth. Sensitivity to weak tones will be degraded somewhat.

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This commit is contained in:
Steve Franke 2019-02-23 14:18:22 -06:00
parent 5d914a1eb1
commit 17ac99344c
2 changed files with 18 additions and 5 deletions
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2
lib/ft8/gen_ft8wave.f90
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@ -17,7 +17,7 @@ subroutine gen_ft8wave(itone,nsym,nsps,fsample,f0,cwave,wave,icmplx,nwave)
twopi=8.0*atan(1.0) twopi=8.0*atan(1.0)
dt=1.0/fsample dt=1.0/fsample
hmod=1.0 hmod=1.0
bt=1.0 bt=1.5
! Compute the frequency-smoothing pulse ! Compute the frequency-smoothing pulse
do i=1,3*nsps do i=1,3*nsps
tt=(i-1.5*nsps)/real(nsps) tt=(i-1.5*nsps)/real(nsps)

21
lib/symspec.f90
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@ -48,10 +48,23 @@ subroutine symspec(shared_data,k,ntrperiod,nsps,ingain,nminw,pxdb,s, &
if(nfft3.ne.nfft3z) then if(nfft3.ne.nfft3z) then
! Compute new window ! Compute new window
pi=4.0*atan(1.0) pi=4.0*atan(1.0)
width=0.25*nsps ! width=0.25*nsps
! do i=1,nfft3
! z=(i-nfft3/2)/width
! w3(i)=exp(-z*z)
! enddo
! Coefficients taken from equation 37 of NUSC report:
! "Some windows with very good sidelobe behavior: application to
! discrete Hilbert Transform, by Albert Nuttall"
!
a0=0.3635819
a1=0.4891775;
a2=0.1365995;
a3=0.0106411;
do i=1,nfft3 do i=1,nfft3
z=(i-nfft3/2)/width w3(i)=a0-a1*cos(2*pi*(i-1)/(nfft3))+ &
w3(i)=exp(-z*z) a2*cos(4*pi*(i-1)/(nfft3))+ &
a3*cos(6*pi*(i-1)/(nfft3))
enddo enddo
nfft3z=nfft3 nfft3z=nfft3
endif endif
@ -86,7 +99,7 @@ subroutine symspec(shared_data,k,ntrperiod,nsps,ingain,nminw,pxdb,s, &
enddo enddo
ihsym=ihsym+1 ihsym=ihsym+1
! xc(0:nfft3-1)=w3(1:nfft3)*xc(0:nfft3-1) !Apply window w3 xc(0:nfft3-1)=w3(1:nfft3)*xc(0:nfft3-1) !Apply window w3
call four2a(xc,nfft3,1,-1,0) !Real-to-complex FFT call four2a(xc,nfft3,1,-1,0) !Real-to-complex FFT
df3=12000.0/nfft3 !JT9-1: 0.732 Hz = 0.42 * tone spacing df3=12000.0/nfft3 !JT9-1: 0.732 Hz = 0.42 * tone spacing