WSJT-X/lib/freqcal.f90
Steven Franke 68b48b7262 Improve accuracy of frequency estimate for non-fading, phase-stable, high-SNR signals.
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@7484 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
2017-01-12 03:48:18 +00:00

85 lines
2.0 KiB
Fortran

subroutine freqcal(id2,k,nkhz,noffset,ntol,line)
parameter (NZ=30*12000,NFFT=55296,NH=NFFT/2)
integer*2 id2(0:NZ-1)
complex sp,sn
real x(0:NFFT-1)
real xi(0:NFFT-1)
real w(0:NFFT-1) !Window function
real s(0:NH)
character line*80,cflag*1
logical first
complex cx(0:NH)
equivalence (x,cx)
data n/0/,k0/9999999/,first/.true./
save n,k0,w,first,pi,fs,xi
if(first) then
pi=4.0*atan(1.0)
fs=12000.0
do i=0,NFFT-1
ww=sin(i*pi/NFFT)
w(i)=ww*ww/NFFT
xi(i)=2.0*pi*i
enddo
first=.false.
endif
if(k.lt.NFFT) go to 900
if(k.lt.k0) n=0
k0=k
x=w*id2(k-NFFT:k-1) !Apply window
call four2a(x,NFFT,1,-1,0) !Compute spectrum, r2c
df=fs/NFFT
if (ntol.gt.noffset) then
ia=0
ib=nint((noffset*2)/df)
else
ia=nint((noffset-ntol)/df)
ib=nint((noffset+ntol)/df)
endif
smax=0.
s=0.
do i=ia,ib
s(i)=real(cx(i))**2 + aimag(cx(i))**2
if(s(i).gt.smax) then
smax=s(i)
ipk=i
endif
enddo
call peakup(s(ipk-1),s(ipk),s(ipk+1),dx)
fpeak=df * (ipk+dx)
ap=(fpeak/fs+1.0/(2.0*NFFT))
an=(fpeak/fs-1.0/(2.0*NFFT))
sp=sum(id2((k-NFFT):k-1)*cmplx(cos(xi*ap),-sin(xi*ap)))
sn=sum(id2((k-NFFT):k-1)*cmplx(cos(xi*an),-sin(xi*an)))
fpeak=fpeak+fs*(abs(sp)-abs(sn))/(abs(sp)+abs(sn))/(2*NFFT)
xsum=0.
nsum=0
do i=ia,ib
if(abs(i-ipk).gt.10) then
xsum=xsum+s(i)
nsum=nsum+1
endif
enddo
ave=xsum/nsum
snr=db(smax/ave)
pave=db(ave) + 8.0
cflag=' '
if(snr.lt.20.0) cflag='*'
n=n+1
nsec=mod(time(),86400)
nhr=nsec/3600
nmin=mod(nsec/60,60)
nsec=mod(nsec,60)
ncal=1
ferr=fpeak-noffset
write(line,1100) nhr,nmin,nsec,nkhz,ncal,noffset,fpeak,ferr,pave, &
snr,cflag,char(0)
1100 format(i2.2,':',i2.2,':',i2.2,i7,i3,i6,2f10.3,2f7.1,2x,a1,a1)
900 return
end subroutine freqcal