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Last update December 03. 2002

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WSJT is the name of a computer program. It stands for "Weak Signal communications, by K1JT", and plans call for the program to include more than one communication mode.


Current version: WSJT v3.0


DEFINITION AND SPECIFICATION OF THE FSK441 ENCODING SCHEME USED IN WSJT

By Joe Taylor, K1JT July 29, 2001

WSJT is the name of a computer program. It stands for "Weak Signal communications, by K1JT", and plans call for the program to include more than one communication mode. The first mode implemented, and the one that has given WSJT its wide initial popularity, is called FSK441. It is designed for high speed meteor scatter (HSMS) communication using "pings" reflected from the underdense ionization trails of random meteors at about 100 km height. Such pings are typically a few dB above the noise and last for anywhere from ten to a few hundred milliseconds. 

FSK441 uses Frequency Shift Keying at a baud rate of 441 Hz. Four distinct tones are used, namely 882, 1323, 1764, and 2205 Hz. Each encoded character uses three tone intervals and therefore requires 3/441 seconds (approximatelt 2.3 ms) for its transmission. FSK441 accommodates a potential "alphabet" of 48 characters. The present encoding scheme uses 43 of these characters, the same ones used in the PUA-43 alphabet. The present encoding of each character is defined in the table below. The four tones are labeled 0-3 for the tones 882 through 2205 Hz, in increasing order. The four possible "single-tone" encodings, namely 000, 111, 222, and 333, are reserved in WSJT for special use as shorthand messages. (These characters sent repeatedly amount to pure single-frequency carriers, and their pings are easily recognized by the software and by the human ear.) The present definition of the shorthand messages is respectively "R26", "R27", "RRR", and "73". These messages are very widely used in North American HSMS communications. 

Character Number Tones sent  Character










10 
11 
12 
13 
14 
15 
16 
17 
18 
19 
20 
21 
22 
23 
24 
25 
26 
27 
28 
29 
30 
31 
32 
33 
34 
35 
36 
37 
38 
39 
40 
41 
42 
43 
44 
45 
46 
47 
...
63
000
001
002
003
010
011
012
013
020
021 
022 
023 
030 
031 
032 
033
100
101
102
103
110
111 
112
113
120
121
122
123
130
131
132
133
200
201
202
203
210
211
212
213
220
221
222
223
230
231
232
233
...
333
[reserved]
1
2
3
4
5
6
7
8
9
.
,
?
/
#
Space>
$
A
B
C
D
[reserved]
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
[reserved]
0
E
Z



[reserved]