1subroutine ccf65(ss,nhsym,ssmax,sync1,dt1,flipk,syncshort,snr2,dt2)
2
3  parameter (NFFT=512,NH=NFFT/2)
4  real ss(322)                     !Input: half-symbol normalized powers
5  real s(NFFT)                     !CCF = ss*pr
6  complex cs(0:NH)                 !Complex FT of s
7  real s2(NFFT)                    !CCF = ss*pr2
8  complex cs2(0:NH)                !Complex FT of s2
9  real pr(NFFT)                    !JT65 pseudo-random sync pattern
10  complex cpr(0:NH)                !Complex FT of pr
11  real pr2(NFFT)                   !JT65 shorthand pattern
12  complex cpr2(0:NH)               !Complex FT of pr2
13  real tmp1(322)
14  real ccf(-11:54)
15  logical first
16  integer npr(126)
17  data first/.true./
18  equivalence (s,cs),(pr,cpr),(s2,cs2),(pr2,cpr2)
19  save
20
21! The JT65 pseudo-random sync pattern:
22  data npr/                                        &
23      1,0,0,1,1,0,0,0,1,1,1,1,1,1,0,1,0,1,0,0,     &
24      0,1,0,1,1,0,0,1,0,0,0,1,1,1,0,0,1,1,1,1,     &
25      0,1,1,0,1,1,1,1,0,0,0,1,1,0,1,0,1,0,1,1,     &
26      0,0,1,1,0,1,0,1,0,1,0,0,1,0,0,0,0,0,0,1,     &
27      1,0,0,0,0,0,0,0,1,1,0,1,0,0,1,0,1,1,0,1,     &
28      0,1,0,1,0,0,1,1,0,0,1,0,0,1,0,0,0,0,1,1,     &
29      1,1,1,1,1,1/
30
31  if(first) then
32! Initialize pr, pr2; compute cpr, cpr2.
33     fac=1.0/NFFT
34     do i=1,NFFT
35        pr(i)=0.
36        pr2(i)=0.
37        k=2*mod((i-1)/8,2)-1
38        if(i.le.NH) pr2(i)=fac*k
39     enddo
40     do i=1,126
41        j=2*i
42        pr(j)=fac*(2*npr(i)-1)
43! Not sure why, but it works significantly better without the following line:
44!        pr(j-1)=pr(j)
45     enddo
46     call four2a(cpr,NFFT,1,-1,0)
47     call four2a(cpr2,NFFT,1,-1,0)
48     first=.false.
49  endif
50
51! Look for JT65 sync pattern and shorthand square-wave pattern.
52  ccfbest=0.
53  ccfbest2=0.
54  do i=1,nhsym-1
55     s(i)=min(ssmax,ss(i)+ss(i+1))
56!     s(i)=ss(i)+ss(i+1)
57  enddo
58
59  call pctile(s,nhsym-1,50,base)
60  s(1:nhsym-1)=s(1:nhsym-1)-base
61  s(nhsym:NFFT)=0.
62  call four2a(cs,NFFT,1,-1,0)               !Real-to-complex FFT
63  do i=0,NH
64!     cs2(i)=cs(i)*conjg(cpr2(i))            !Mult by complex FFT of pr2
65     cs(i)=cs(i)*conjg(cpr(i))              !Mult by complex FFT of pr
66  enddo
67  call four2a(cs,NFFT,1,1,-1)               !Complex-to-real inv-FFT
68!  call four2a(cs2,NFFT,1,1,-1)              !Complex-to-real inv-FFT
69
70  do lag=-11,54                             !Check for best JT65 sync
71     j=lag
72     if(j.lt.1) j=j+NFFT
73     ccf(lag)=s(j)
74!     if(abs(ccf(lag)).gt.ccfbest) then
75     if(ccf(lag).gt.ccfbest) then           !No inverted sync for use at HF
76!        ccfbest=abs(ccf(lag))
77        ccfbest=ccf(lag)
78        lagpk=lag
79        flipk=1.0
80!        if(ccf(lag).lt.0.0) flipk=-1.0
81     endif
82  enddo
83
84!  do lag=-11,54                             !Check for best shorthand
85!     ccf2=s2(lag+28)
86!     if(ccf2.gt.ccfbest2) then
87!        ccfbest2=ccf2
88!        lagpk2=lag
89!     endif
90!  enddo
91
92! Find rms level on baseline of "ccfblue", for normalization.
93  sum=0.
94  do lag=-11,54
95     if(abs(lag-lagpk).gt.1) sum=sum + ccf(lag)
96  enddo
97  base=sum/50.0
98  sq=0.
99  do lag=-11,54
100     if(abs(lag-lagpk).gt.1) sq=sq + (ccf(lag)-base)**2
101  enddo
102  rms=sqrt(sq/49.0)
103  sync1=ccfbest/rms - 4.0
104  dt1=lagpk*(2048.0/11025.0) - 2.5
105
106! Find base level for normalizing snr2.
107  do i=1,nhsym
108     tmp1(i)=ss(i)
109  enddo
110  call pctile(tmp1,nhsym,40,base)
111  snr2=0.398107*ccfbest2/base                !### empirical
112  syncshort=0.5*ccfbest2/rms - 4.0           !### better normalizer than rms?
113!  dt2=(2.5 + lagpk2*(2048.0/11025.0))
114  dt2=0.
115
116  return
117end subroutine ccf65
118