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More edits to jtms3.txt.

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git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/jtms3@2488 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
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Joe Taylor 2012-07-04 22:18:52 +00:00
parent 5a551b3435
commit afcf99d990
2 changed files with 21 additions and 21 deletions
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40
jtms3.txt
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@ -12,11 +12,10 @@ sync bits are inserted, spread evenly so as to fall at positions 1, 7,
and 43 sync bits. Frame duration is 129 ms. and 43 sync bits. Frame duration is 129 ms.
Type 2 messages convey 4 user information bits (report, R+report, RRR, Type 2 messages convey 4 user information bits (report, R+report, RRR,
73) encoded with a (15,4,8) block code, plus a 12-bit CRC for each 73) encoded with a (15,4,8) block code, plus an 11-bit CRC derived
callsign, encoded with the Golay (23,12) code. This makes for 15 + from MyCall + HisCall, encoded with the (16,11) extended Hamming code.
2*23 = 61 information-carrying bits. One dummy bit is added, and the This makes for 31 information-carrying bits. They are interspersed
62 bits are interspersed with 31 sync bits, making a frame of 93 bits with 31 sync bits, making a frame of 62 bits and frame time 31 ms.
and frame time 46.5 ms.
2. Modulation is BPSK at 2000 baud, 24 samples per symbol at 48000 Hz 2. Modulation is BPSK at 2000 baud, 24 samples per symbol at 48000 Hz
asmple rate. The baseband waveform is built by inserting a tapered asmple rate. The baseband waveform is built by inserting a tapered
@ -24,21 +23,21 @@ sinc function for each bit, then multiplying by a 1500 Hz sine wave.
3. Receiving 3. Receiving
a. Compute real-to-complex windowed FFTs, N=12288 (t=256 ms), a. Compute real-to-complex windowed FFTs, N=16384 (t=341 ms),
stepped by 128 ms (say). Zap birdies, remove frequency stepped by 8k (say). Zap birdies, remove frequency components
components outside the range 300 - 2700 Hz, and convert to an outside the range 300 - 2700 Hz, and convert to analytic
analytic time-domain signal. time-domain signal.
b. Square the complex signal, cx2=cx*cx, and compute N=12288 FFT of b. Square the complex signal, cx2=cx*cx, and compute N=8k FFT of
cx2 (resolution = 3.9 Hz). Look for carrier at 3000 + 2*DF Hz cx2 (resolution = 5.9 Hz). Look for carrier at 3000 + 2*DF Hz
+/- 2*Tol. +/- 2*Tol.
c. If carrier is found, measure frequency f and phase phi. Multiply c. If carrier is found, measure frequency f and phase phi. Multiply
cx by exp(-twopi*i*f*t - phi) to recover the real baseband signal cx by exp(-twopi*i*f*t - phi) to recover the real baseband signal
x() to within a sign ambiguity. x() to within a sign ambiguity.
d. Apply matched filter for the Tx pulse shape to x(). (This is just d. Apply matched filter for the Tx pulse shape to x(). This is
a rectangular BPF, 500 - 25-- Hz ?) essentially a rectangular BPF, -1000 to +1000 Hz ?
e. Establish PSK symbol sync (offset i0, 0 to nsps-1 samples) by finding e. Establish PSK symbol sync (offset i0, 0 to nsps-1 samples) by finding
maximum of Sum(sum*sum) over groups of nsps consecutive samples. maximum of Sum(sum*sum) over groups of nsps consecutive samples.
@ -48,18 +47,19 @@ sinc function for each bit, then multiplying by a 1500 Hz sine wave.
its 43 positions) and three of the 31-bit sync vector (rotated by its 43 positions) and three of the 31-bit sync vector (rotated by
0, 10, 20 of 31). 0, 10, 20 of 31).
g. If the best CCF abs(peak) exceeds a specified threshold, the sign g. If the best CCF abs(peak) exceeds a specified threshold, the
of peak resolves the sign ambiguity. signal is detected and synchronized. Sign of peak resolves the
sign ambiguity.
h. For Type 1 messages: Gather the proper set of 215 h. For Type 1 messages: Gather the proper set of 215
information-carrying soft symbols. Form averages using the 9 information-carrying soft symbols. Form averages using the 9
extra symbols, reducing the number to 206, and remove extra symbols, reducing the number to 206; and remove
interleaving to re-order the symbols. Then run the fano232 interleaving to re-order the symbols. Then run the fano232
decoder. If decoding fails, add soft symbols into an decoder. If decoding fails, add soft symbols into an
accumulation array and (if nsum is 2 or more) try decoding the accumulation array and (if nsum is 2 or more) try decoding the
average. average.
i. For Type 2 messages: Gather the proper set of 62 soft symbols. i. For Type 2 messages: Gather the proper set of 31 soft symbols.
Decode Nrpt using an exhaustive search over all possibilities. Decode Nrpt using exhaustive search (find peak lag of ccf). For
For the CRCs, also do exhaustive searches -- and make sure that the CRC, also do an exhaustive search -- and make sure that the
the expected values are best (or fall in the top few, anyway). expected value is best (or in the top few, anyway).

2
mainwindow.cpp
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@ -1,4 +1,4 @@
//--------------------------------------------------------------- MainWindow //-------------------------------------------------------------- MainWindow
#include "mainwindow.h" #include "mainwindow.h"
#include "ui_mainwindow.h" #include "ui_mainwindow.h"
#include "devsetup.h" #include "devsetup.h"