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WSJT-X
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Try to ensure that nfft1 and nfft2 are nice values. Add a brickwall filter in the downsampler.

This commit is contained in:
Steven Franke 2020-06-29 12:15:28 -05:00
parent 83fddb1f57
commit 06b8e0eec6
1 changed files with 27 additions and 11 deletions
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38
lib/fst240_decode.f90
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@ -76,26 +76,38 @@ contains
nmax=15*12000
ndown=20/hmod !nss=40,80,160,400
if(hmod.eq.8) ndown=2
nfft1=int(nmax/ndown)*ndown
else if(ntrperiod.eq.30) then
nsps=1680
nmax=30*12000
ndown=42/hmod !nss=40,80,168,336
if(hmod.eq.4) ndown=10
if(hmod.eq.8) ndown=5
nfft1=359856
if(hmod.eq.4) then
ndown=10
nfft1=nmax
endif
if(hmod.eq.8) then
ndown=5
nfft1=nmax
endif
nfft1=int(nmax/ndown)*ndown
else if(ntrperiod.eq.60) then
nsps=3888
nmax=60*12000
ndown=96/hmod !nss=36,81,162,324
if(hmod.eq.1) ndown=108
nfft1=int(719808/ndown)*ndown
else if(ntrperiod.eq.120) then
nsps=8200
nmax=120*12000
ndown=200/hmod !nss=40,82,164,328
if(hmod.eq.1) ndown=205
nfft1=int(nmax/ndown)*ndown
else if(ntrperiod.eq.300) then
nsps=21504
nmax=300*12000
ndown=512/hmod !nss=42,84,168,336
nfft1=int((nmax-200)/ndown)*ndown
end if
nss=nsps/ndown
fs=12000.0 !Sample rate
@ -105,16 +117,17 @@ contains
dt2=1.0/fs2
tt=nsps*dt !Duration of "itone" symbols (s)
baud=1.0/tt
nfft1=2*int(nmax/2)
nh1=nfft1/2
sigbw=4.0*hmod*baud
nfft2=nfft1/ndown !make sure that nfft1 is exactly nfft2*ndown
nfft1=nfft2*ndown
nh1=nfft1/2
allocate( r_data(1:nfft1+2) )
allocate( c_bigfft(0:nfft1/2) )
nfft2=nfft1/ndown
allocate( c2(0:nfft2-1) )
allocate( cframe(0:164*nss-1) )
allocate( cframe(0:160*nss-1) )
npts=nmax
if(single_decode) then
fa=max(100,nint(nfqso+1.5*hmod*baud-ntol))
fb=min(4800,nint(nfqso+1.5*hmod*baud+ntol))
@ -164,7 +177,7 @@ contains
! Output array c2 is complex baseband sampled at 12000/ndown Sa/sec.
! The size of the downsampled c2 array is nfft2=nfft1/ndown
call fst240_downsample(c_bigfft,nfft1,ndown,fc0,c2)
call fst240_downsample(c_bigfft,nfft1,ndown,fc0,sigbw,c2)
call timer('sync240 ',0)
do isync=0,1
@ -257,7 +270,7 @@ contains
fc_synced=candidates(icand,3)
isbest=nint(candidates(icand,4))
xdt=(isbest-nspsec)/fs2
call fst240_downsample(c_bigfft,nfft1,ndown,fc_synced,c2)
call fst240_downsample(c_bigfft,nfft1,ndown,fc_synced,sigbw,c2)
do ijitter=0,jittermax
if(ijitter.eq.0) ioffset=0
@ -462,7 +475,7 @@ contains
return
end subroutine sync_fst240
subroutine fst240_downsample(c_bigfft,nfft1,ndown,f0,c1)
subroutine fst240_downsample(c_bigfft,nfft1,ndown,f0,sigbw,c1)
! Output: Complex data in c(), sampled at 12000/ndown Hz
@ -471,9 +484,12 @@ contains
df=12000.0/nfft1
i0=nint(f0/df)
ih=nint( ( f0 + 1.2*sigbw/2.0 )/df)
nbw=ih-i0+1
c1=0.
c1(0)=c_bigfft(i0)
nfft2=nfft1/ndown
do i=1,nfft2/2
do i=1,nbw
if(i0+i.le.nfft1/2) c1(i)=c_bigfft(i0+i)
if(i0-i.ge.0) c1(nfft2-i)=c_bigfft(i0-i)
enddo