mirror of
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Now have a properly functioning stand-along decoder for JTMSK.
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/jtms3@2529 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
This commit is contained in:
Joe Taylor
parent
160009e621
commit
5079669e49
92
jtmsk.txt
92
jtmsk.txt
@ -1,64 +1,72 @@
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JTMSK: Possible New Mode for Meteor Scatter
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-------------------------------------------
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JTMSK is a digital mode designed for amateur meteor-scatter
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communication. The "MSK" part of the name could mean "Meteor Scatter
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King": the mode works at the same signal levels as the popular mode
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FSK441, but at about twice the character transmission rate, so it
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makes much better use of short pings. MSK also means "Minimum Shift
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Keying", which is the modulation technique used in JTMSK. It is a
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form of continuous-phase frequency-shift keying that achieves high
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transmission rate with a narrow bandwidth, while maintaining a
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constant-envelope waveform.
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1. Transmitting
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Messages are sent character-by character, 6 bits plus odd parity.
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Message length can be one of {5 7 9 11 13 17 19 23 29}; messages are
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padded with blanks up to the next available length from this list.
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Message length in characters is automatically selected from among the
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possibilities 5 7 9 11 13 17 19 23 29. (Note that these lengths share
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no common factor.) Messages are padded with blanks when required, up
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to the next available length.
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Modulation is Minimum Shift Keying (MSK) at 2000 baud. This is a form
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of constant-envelope, continuous-phase modulation, equivalent to FSK
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with offset equal to half the bit rate. JTMSK sends a "0" bit with
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0.5 ms of a sine wave at f0=1000 Hz, and a "1" bit at f1=2000 Hz.
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Carrier phase increment over one bit is therefore 0.5 cycles (pi
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radians) at f0 and 1.0 cycles (two*pi radians) at f1. With odd parity
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there is always an odd number of 1's and even number of 0's in a
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character, so the phase increment over a full character is always an
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integer number of cycles.
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Modulation is Minimum Shift Keying (MSK) at 2000 baud. A "0" bit is
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sent as an audio sine wave at f0=1000 Hz, lasting 0.5 ms; a "1" bit is
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a sine wave at f1=2000 Hz. The carrier phase increment over one bit
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is thus 0.5 cycles (pi radians) at f0, or 1.0 cycles at f1. Odd
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parity assures an odd number of 1's and even number of 0's in every
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7-bit character, so the phase increment over a full character is
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always an integer number of cycles.
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2. Receiving
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a. Pings are detected (or mouse-picked data is selected) as in
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WSJT9, except that it's done in real time rather than at the end
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of an Rx interval.
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a. Detect pings and update display in real time. (rtping)
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b. Compute real-to-complex FFT. Zap birdies, remove frequency
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components outside the range 300 - 2700 Hz, and convert to analytic
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b. Compute real-to-complex FFT. Zap birdies, remove frequency
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components outside the range 300 - 2700 Hz, convert to analytic
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time-domain signal. (analytic)
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c. Square the complex signal, cx2=cx*cx, and compute FFT. Look for
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narrow carriers at frequency 2000 + 2*DF +/- 2*Tol and 2000 Hz
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higher. (msdf)
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c. Square the complex signal and compute FFT. Look for narrow
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spectral lines at frequency 2000 + 2*(DF +/- Tol) Hz and
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4000 + 2*(DF +/- Tol) Hz. (msdf)
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d. If carrier is found, measure frequency f and phase phi. Multiply
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cx by exp(-twopi*i*(f-1500)*t - phi) to recover the
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standard-frequency baseband signal. (tweak1)
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d. If a signal is found, measure frequency offset DF and phase Dphi.
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(DF and Dphi are measured relative to the original frequencies f0
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and f1, not their doubled values.) Multiply cx by
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exp(-twopi*i*DF*t - Dphi) to recover the standard-frequency
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baseband signal. (tweak1)
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e. Establish symbol and character sync by cross-correlating with
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conjg(cwb), where cwb is the MSK waveform for the <space>
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character.
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conjg(cwb), MSK waveform for the <space> character.
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f. Find message length by computing ACF (of what? cdat? soft
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symbol values?)
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f. Find message length by computing ACF.
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g. Cross-correlate the complex standard-frequency signal against
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conjugated templates for each character in the JTMSK alphabet.
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Best match yields the decoded character.
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h. Decode the message by cross-correlating character-length segments
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g. Decode the message by cross-correlating character-length segments
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of cdat against complex waveforms for each possible character.
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i. If msglen is established and long enough, try folding the data and
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determining best-fit characters as above.
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h. If ping is long enough, try folding the data and determining the
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best-fit characters as above.
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3. Comparison of modes:
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3. Parameters of fast modes:
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| Meteor Scatter | IonoScatter
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| FSK441 JTMS JTMSK | JT6M ISCAT
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-------------------+-----------------------+-------------------
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T/R period (s) | 30 30 30 | 30 30
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Modulation type | 4-FSK MSK* MSK* | 44-FSK 41-FSK
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Keying rate (baud) | 441 1378 2000 | 21.5 43.1
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Characters/s | 147 197 286 | 14.3 32.3
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Bandwidth (Hz) | 1764 1378 2000 | 947 1809
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+--------------------+-----------------------+-------------------+
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| | Meteor Scatter | IonoScatter |
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| | FSK441 JTMS JTMSK | JT6M ISCAT |
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+--------------------+-----------------------+-------------------|
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| T/R period (s) | 30 30 30 | 30 30 |
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| Modulation type | 4-FSK MSK MSK | 44-FSK 41-FSK |
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| Keying rate (baud) | 441 1378 2000 | 21.5 43.1 |
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| Bit rate (bps) | 882 1378 2000 | - - |
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| Characters/s | 147 197 286 | 14.3 32.3 |
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| Bandwidth (Hz) | 1764 1378 2000 | 947 1809 |
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+--------------------+-----------------------+-------------------+
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@ -1,14 +1,14 @@
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subroutine jtmsk(dat,npts,cfile6,t2,mswidth,ndb,nrpt,Nfreeze, &
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ntol,MouseDF,pick)
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subroutine jtmsk(dat,npts,cfile6,tpk,mswidth,ndb,nrpt,Nfreeze, &
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ntol,MouseDF,pick,mycall)
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! Decode a JTMS ping
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! Decode a JTMSK ping
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parameter (NZ=30*48000)
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parameter (NZ=2*48000)
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real dat(npts) !Raw data
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complex cdat(NZ) !Analytic form of signal
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character*6 cfile6 !FileID
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logical pick
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character*12 mycall,hiscall
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character*12 mycall
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real s(NZ) !Power spectrum
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real s2(0:63,400)
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real r(60000)
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@ -16,8 +16,6 @@ subroutine jtmsk(dat,npts,cfile6,t2,mswidth,ndb,nrpt,Nfreeze, &
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complex cwb(168) !Complex waveform for <space>
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logical first
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character msg*400,msg29*29
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character*90 line
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common/ccom/nline,tping(100),line(100)
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data first/.true./
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save first,cw,cwb
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save cdat !Fix its address, for four2
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@ -31,56 +29,44 @@ subroutine jtmsk(dat,npts,cfile6,t2,mswidth,ndb,nrpt,Nfreeze, &
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nfft1=2**n !FFT length
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call analytic(dat,npts,nfft1,s,cdat) !Convert to analytic signal
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call mskdf(cdat,npts,t2,nfft1,f0,nfreeze,mousedf,ntol, &
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call mskdf(cdat,npts,tpk,nfft1,f0,nfreeze,mousedf,ntol, &
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dfx,snrsq2) !Get DF
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print*,'b',dfx,snrsq2
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sq2lim=7.0
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if(pick) sq2lim=5.0
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if(snrsq2.lt.sq2lim) go to 900 !Reject non-JTMS signals
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if(snrsq2.lt.sq2lim) go to 900 !Reject non-JTMS signals
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call tweak1(cdat,npts,-dfx,cdat) !Mix to standard frequency
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! DF is known, now establish character sync.
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call syncmsk(cdat,npts,cwb,r,i1) !Get character sync
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call syncmsk(cdat,npts,cwb,r,i1) !Get character sync
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call lenmsk(r,npts,msglen) !Find message length
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call lenmsk(r,npts,msglen) !Find message length
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s2=0.
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nchar=(npts-168+1-i1)/168
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if(nchar.gt.400) nchar=400
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call decodemsk(cdat,npts,cw,i1,nchar,s2,msg) !Decode the message
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print*,'B',i1,msglen,nchar
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print*,msg(1:nchar)
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! ia=1
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! if(nchar.ge.40) ia=min(nchar/3,nchar-28)
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! ib=min(ia+28,nchar) !Can better limits ia, ib be found?
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! print*,'A',ia,ib,nchar
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! print*,msg(1:nchar)
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! msg29=adjustl(msg(ia:ib))
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ia=1
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if(nchar.ge.40) ia=min(nchar/3,nchar-28)
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ib=min(ia+28,nchar) !Can better limits ia, ib be found?
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msg29=adjustl(msg(ia:ib))
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msg=adjustl(msg)
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ib=min(nchar,45)
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ndf=nint(dfx)
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nchk=max(20,nint(1.5*msglen))
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if(msglen.eq.0 .or. nchar.lt.nchk .or. pick) then
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if(nline.le.99) nline=nline+1
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tping(nline)=t2
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write(line(nline),1110) cfile6,t2,mswidth,ndb,nrpt,ndf,msg(1:45)
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write(*,1110) cfile6,tpk,mswidth,ndb,nrpt,ndf,msg(1:45)
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1110 format(a6,f5.1,i5,i3,1x,i2.2,i5,5x,a45)
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endif
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if(msglen.gt.0 .and. nchar.ge.nchk) then
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call foldmsk(s2,msglen,nchar,mycall,msg,msg29) !Decode folded message
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if(nline.le.99) nline=nline+1
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tping(nline)=t2
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write(line(nline),1120) cfile6,t2,mswidth,ndb,nrpt,ndf,msg29
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write(*,1120) cfile6,tpk,mswidth,ndb,nrpt,ndf,msg29
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1120 format(a6,f5.1,i5,i3,1x,i2.2,i5,5x,a29,11x,'*')
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endif
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900 continue
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return
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end subroutine jtmsk
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@ -1,11 +1,12 @@
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program msk
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! Starting code for a JTMSK decoder.
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! Program to test decoding routines for mode JTMSK.
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parameter (NSMAX=30*48000)
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character*80 infile
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character*6 cfile6
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character*12 arg
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character*12 mycall
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real dat(NSMAX)
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real x(NSMAX)
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complex cx(0:NSMAX/2)
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@ -14,46 +15,49 @@ program msk
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common/mscom/id(NSMAX),s1(215,703),s2(215,703)
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nargs=iargc()
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if(nargs.lt.1) then
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print*,'Usage: msk <snr>'
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if(nargs.lt.2) then
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print*,'Usage: msk nslow snr'
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go to 999
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endif
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call getarg(1,arg)
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read(arg,*) nslow
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call getarg(2,arg)
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read(arg,*) snr
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! Read simulated pings from a file
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open(71,file='dat.71',form='unformatted',status='old')
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read(71) id
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cfile6='123400'
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cfile6='123400'
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npts=30*48000
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kstep=2048
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minsigdb=6
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minsigdb=1
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mousedf=0
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ntol=200
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mycall='W8WN'
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! Make some band-limited noise.
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call random_number(x)
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nfft=NSMAX
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call four2a(x,nfft,1,-1,0)
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df=48000.0/nfft
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ia=nint(300.0/df)
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ib=nint(2800.0/df)
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ib=nint(2700.0/df)
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cx(:ia)=0.
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cx(ib:)=0.
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call four2a(cx,nfft,1,1,-1)
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x(1)=0.
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sq=0.
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do i=1,NSMAX
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sq=sq + x(i)**2
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enddo
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rms=sqrt(sq/NSMAX)
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rms=sqrt(dot_product(x,x)/NSMAX)
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x=x/rms
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sig=(10.0**(0.05*snr))/32768.0
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dat=sig*id + x
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k=0
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sig=(10.0**(0.05*snr))/32768.0 !Scaled signal strength
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dat=sig*id + x !Add pings to noise
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! This loop simulates being called from "datasink()" in program JTMSK.
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do iblk=1,npts/kstep
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k=k+kstep
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call rtping(dat,k,cfile6,MinSigdB,MouseDF,ntol)
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k=iblk*kstep
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call rtping(dat,k,cfile6,MinSigdB,MouseDF,ntol,mycall)
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if(nslow.ne.0) call usleep(42000)
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enddo
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999 end program msk
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@ -1,103 +1,92 @@
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subroutine rtping(dat,k,cfile6,MinSigdB,MouseDF,ntol)
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subroutine rtping(dat,k,cfile6,MinSigdB,MouseDF,ntol,mycall)
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!subroutine rtping(dat,jz,nz,MinSigdB,MinWidth,NFreeze,DFTolerance, &
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! MouseDF,istart,pick,cfile6,mycall,hiscall,mode,ps0)
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! Decode Multi-Tone FSK441 mesages.
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! Called from datasink() every 2048 sample intervals (approx 43 ms).
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! Detects pings (signal level above MinSigdB). When a ping ends, its
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! MSK signal is synchronized and decoded.
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parameter (NSMAX=30*48000)
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parameter (NZMAX=NSMAX/2048)
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parameter (NZMAX=703) !703 = NSMAX/2048
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real dat(NSMAX) !Raw audio data
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logical pick
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character*6 cfile6
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character*6 cfile6 !Time hhmmss at start of this Rx interval
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character*12 mycall
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real sig(NZMAX) !Sq-law detected signal, sampled at 43 ms
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real sigdb(NZMAX) !Signal in dB, sampled at 43 ms
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real work(NZMAX)
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real pingdat(3,100)
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! character msg*40,msg3*3
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character*90 line
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common/ccom/nline,tping(100),line(100)
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data nping0/0/
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real tmp(NZMAX)
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logical inside,pingFound
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data k0/9999999/
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save
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if(k.lt.k0) then
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inside=.false.
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pingFound=.false.
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j0=0
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t1=0.
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width=0.
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peak=0.
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tpk=0.
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dt=1.0/48000.0
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kstep=2048
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sdt=dt*kstep
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wmin=0.043
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endif
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k0=k
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slim=MinSigdB
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! nf1=-ntol
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! nf2=ntol
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dt=1.0/48000.0
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kstep=2048
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! pick=.false.
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istart=1
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jz=k
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snrlim=10.0**(0.1*slim) - 1.0
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sdown=10.0*log10(0.25*snrlim+1.0)
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! Find signal power
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j=k/kstep
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sig(j)=dot_product(dat(k-kstep+1:k),dat(k-kstep+1:k))/kstep
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if(j.lt.10) return
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if(j.lt.20) return
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! Remove baseline, compute signal level in dB
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call pctile (sig,work,j,50,base1)
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do i=1,j
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sigdb(i)=db(sig(i)/base1)
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if(j.eq.703) write(13,3001) i,sig(i),sigdb(i)
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3001 format(i5,2e12.3)
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enddo
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! Determine baseline noise level
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if(mod(j,20).eq.0) call pctile (sig,tmp,j,50,base)
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sigdb(j)=db(sig(j)/base) ! (S+N)/N in dB
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dtbuf=kstep*dt
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wmin=0.040
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call ping(sigdb,j,dtbuf,slim,wmin,pingdat,nping)
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! write(72,3001) j*sdt,base,sig(j),sigdb(j)
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!3001 format(f10.3,3f12.6)
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! If this is a "mouse pick" and no ping was found, force a pseudo-ping
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! at center of data.
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! if(pick.and.nping.eq.0) then
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! if(nping.le.99) nping=nping+1
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! pingdat(1,nping)=0.5*jz*dt
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! pingdat(2,nping)=0.16
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! pingdat(3,nping)=1.0
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! endif
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if(sigdb(j).ge.slim .and. .not.inside) then
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j0=j !Mark the start of a ping
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t1=j0*sdt
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inside=.true.
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peak=0.
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endif
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do iping=1,nping
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! Find starting place and length of data to be analyzed:
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tstart=pingdat(1,iping)
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width=pingdat(2,iping)
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peak=pingdat(3,iping)
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! mswidth=10*nint(100.0*width)
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jj=(tstart-0.02)/dt
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if(jj.lt.1) jj=1
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jjz=nint((width+0.02)/dt)+1
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jjz=min(jjz,jz+1-jj)
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if(inside .and. sigdb(j).gt.peak) then
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peak=sigdb(j) !Save peak strength
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tpk=j*sdt ! and time of peak
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endif
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if(inside .and. (sigdb(j).lt.sdown .or. j.eq.NZMAX)) then
|
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width=(j-j0)*sdt !Save ping width
|
||||
if(width.ge.wmin) pingFound=.true.
|
||||
endif
|
||||
if(.not.pingFound) return
|
||||
|
||||
! Compute average spectrum of this ping.
|
||||
! call spec441(dat(jj),jjz,ps,f0)
|
||||
! A ping was found! Assemble a signal report:
|
||||
nwidth=0
|
||||
if(width.ge.0.04) nwidth=1
|
||||
if(width.ge.0.12) nwidth=2
|
||||
if(width.gt.1.00) nwidth=3
|
||||
nstrength=6
|
||||
if(peak.ge.11.0) nstrength=7
|
||||
if(peak.ge.17.0) nstrength=8
|
||||
if(peak.ge.23.0) nstrength=9
|
||||
nrpt=10*nwidth + nstrength
|
||||
|
||||
! Decode the message.
|
||||
! msg=' '
|
||||
! call longx(dat(jj),jjz,ps,DFTolerance,noffset,msg,msglen,bauderr)
|
||||
mswidth=10*nint(100.0*width)
|
||||
i1=(t1-0.02)/dt
|
||||
if(i1.lt.1) i1=1
|
||||
iz=nint((width+0.02)/dt) + 1
|
||||
iz=min(iz,k+1-i1,2*48000) !Length of ping in samples
|
||||
|
||||
! Assemble a signal report:
|
||||
nwidth=0
|
||||
if(width.ge.0.04) nwidth=1 !These might depend on NSPD
|
||||
if(width.ge.0.12) nwidth=2
|
||||
if(width.gt.1.00) nwidth=3
|
||||
nstrength=6
|
||||
if(peak.ge.11.0) nstrength=7
|
||||
if(peak.ge.17.0) nstrength=8
|
||||
if(peak.ge.23.0) nstrength=9
|
||||
! nrpt=10*nwidth + nstrength
|
||||
t2=tstart + dt*(istart-1)
|
||||
call jtmsk(dat(i1),iz,cfile6,tpk,mswidth,int(peak),nrpt, &
|
||||
nfreeze,DFTolerance,MouseDF,pick,mycall)
|
||||
|
||||
jjzz=min(jjz,2*48000) !Max data size 2 s
|
||||
!###
|
||||
jjzz=14400
|
||||
jj=jj-200
|
||||
!###
|
||||
|
||||
if(nping.gt.nping0) then
|
||||
print*,'a',jj,jjzz,jj*dt,jjzz*dt,t2,width
|
||||
call jtmsk(dat(jj),jjzz,cfile6,t2,mswidth,int(peak),nrpt, &
|
||||
nfreeze,DFTolerance,MouseDF,pick)
|
||||
nping0=nping
|
||||
endif
|
||||
enddo
|
||||
pingFound=.false.
|
||||
inside=.false.
|
||||
|
||||
return
|
||||
end subroutine rtping
|
||||
|
||||
@ -1,4 +1,4 @@
|
||||
//--------------------------------------------------------------- MainWindow
|
||||
//---------------------------------------------------------------- MainWindow
|
||||
#include "mainwindow.h"
|
||||
#include "ui_mainwindow.h"
|
||||
#include "devsetup.h"
|
||||
|
||||
Loading…
Reference in New Issue
Block a user