WSJT-X/lib/symspec.f90

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subroutine symspec(k,ntrperiod,nsps,ingain,nb,nbslider,pxdb,s,red, &
df3,ihsym,npts8)
! Input:
! k pointer to the most recent new data
! ntrperiod T/R sequence length, minutes
! nsps samples per symbol, at 12000 Hz
! ndiskdat 0/1 to indicate if data from disk
! nb 0/1 status of noise blanker (off/on)
! nbslider NB setting, 0-100
! Output:
! pxdb power (0-60 dB)
! s() spectrum for waterfall display
! red() first cut at JT9 sync amplitude
! ihsym index number of this half-symbol (1-184)
parameter (NTMAX=120)
parameter (NMAX=NTMAX*12000) !Total sample intervals per 30 minutes
parameter (NDMAX=NTMAX*1500) !Sample intervals at 1500 Hz rate
parameter (NSMAX=1365) !Max length of saved spectra
parameter (NFFT1=1024)
parameter (NFFT2=1024,NFFT2A=NFFT2/8)
parameter (MAXFFT3=32768)
real*4 s(NSMAX),w3(MAXFFT3)
real*4 x1(NFFT1)
real*4 x2(NFFT1+105)
real*4 ssum(NSMAX)
real*4 red(NSMAX)
complex cx(0:MAXFFT3-1)
integer*2 id2
complex c0
common/jt9com/ss(184,NSMAX),savg(NSMAX),c0(NDMAX),id2(NMAX),nutc,ndiskdat, &
ntr,mousefqso,newdat,nfa,nfb,ntol,kin,nzhsym,nsynced,ndecoded
data rms/999.0/,k0/99999999/,ntrperiod0/0/,nfft3z/0/
save
if(ntrperiod.eq.1) nfft3=2048
if(ntrperiod.eq.2) nfft3=2048
if(ntrperiod.eq.5) nfft3=6144
if(ntrperiod.eq.10) nfft3=12288
if(ntrperiod.eq.30) nfft3=32768
jstep=nsps/16 !Step size = half-symbol in c0()
if(k.gt.NMAX) go to 999
if(k.lt.nfft3) then
ihsym=0
go to 999 !Wait for enough samples to start
endif
if(nfft3.ne.nfft3z) then !New nfft3, compute window
pi=4.0*atan(1.0)
if(ntrperiod.eq.1) then !Compute window for nfft3 spectrun
do i=1,nfft3
xx=float(i-1)/(nfft3-1)
w3(i)=0.40897 -0.5*cos(2.0*pi*xx) + 0.09103*cos(4.0*pi*xx)
! w3(i)=0.355768 - 0.487306*cos(2.0*pi*xx) + 0.144232*cos(4.0*pi*xx) &
! - 0.012604*cos(6.0*pi*xx)
enddo
else
do i=1,nfft3
w3(i)=2.0*(sin(i*pi/nfft3))**2 !Window for nfft3 spectrum
enddo
endif
nfft3z=nfft3
endif
if(k.lt.k0) then !Start a new data block
ja=0
ssum=0.
ihsym=0
k1=0
k8=0
x2=0.
if(ndiskdat.eq.0) then
id2(k+1:)=0
c0=0. !This is necessary to prevent "ghosts". Not sure why.
endif
endif
k0=k
kstep1=NFFT1
fac=2.0/NFFT1
nblks=(k-k1)/kstep1
gain=10.0**(0.05*ingain)
sq=0.
do nblk=1,nblks
do i=1,NFFT1
x1(i)=gain*id2(k1+i)
enddo
sq=sq + dot_product(x1,x1)
! Mix at 1500 Hz, lowpass at +/-750 Hz, and downsample to 1500 Hz complex.
x2(106:105+kstep1)=x1(1:kstep1)
call fil3(x2,kstep1+105,c0(k8+1),n2)
x2(1:105)=x1(kstep1-104:kstep1) !Save 105 trailing samples
k1=k1+kstep1
k8=k8+kstep1/8
enddo
npts8=k8
ja=ja+jstep !Index of first sample
rms=sqrt(sq/(nblks*NFFT1))
pxdb=0.
if(rms.gt.0.0) pxdb=20.0*log10(rms)
if(pxdb.gt.60.0) pxdb=60.0
do i=0,nfft3-1 !Copy data into cx
j=ja+i-(nfft3-1)
cx(i)=0.
if(j.ge.1 .and. j.le.NDMAX) cx(i)=c0(j)
enddo
if(ihsym.lt.184) ihsym=ihsym+1
cx(0:nfft3-1)=w3(1:nfft3)*cx(0:nfft3-1) !Apply window w3
call four2a(cx,nfft3,1,1,1) !Third FFT (forward)
n=min(184,ihsym)
df3=1500.0/nfft3 !JT9-a: 0.732 Hz = 0.42 * tone spacing
i0=nint(-500.0/df3)
iz=min(NSMAX,nint(1000.0/df3))
fac=(1.0/nfft3)**2
do i=1,iz
j=i0+i-1
if(j.lt.0) j=j+nfft3
sx=fac*(real(cx(j))**2 + aimag(cx(j))**2)
ss(n,i)=sx
ssum(i)=ssum(i) + sx
s(i)=sx
enddo
999 continue
fac00=0.35
npct=20
call pctile(s,iz,npct,xmed0)
fac0=fac00/max(xmed0,0.006)
s(1:iz)=fac0*s(1:iz)
call pctile(ssum,iz,npct,xmed1)
fac1=fac00/max(xmed1,0.006*ihsym)
savg(1:iz)=fac1*ssum(1:iz)
! savg(iz+1:iz+20)=savg(iz)
call redsync(ss,ntrperiod,ihsym,iz,red)
return
end subroutine symspec