PSK31

PSK means Phase Shifk Keying at 31 baud.
It is a digital communication mode, invented by Peter Martinez (G3PLX) and based on the former SLOWBPSK, by Pawel Jalocha (SP9VRC).
It modulates the phase of a single audio tone, transmitted normally in USB mode, on HF bands and on six meters, or also in FM, on VHF bands and up.
It exists in two variants:

BPSK (0 or 180 degrees phase shifts), where each baud carries 1 bit
QBSK (0, 90, 180 or 270 degrees phase shifts), where it's used a Viterbi convolutional 5 bits code

The transmission is always at 31.25 baud, with a variable length code (Varicode), where characters used more often have shorter bit codes. As a result, the mean transmission rate is about 50 words per minute (wpm).
Standard Varicode has 128 codes (up to 10 bits), for standard Ascii characters, but there is also an extended version, with 256 codes (up to 12 bits each). Spacing between two characters is coded as a minimum of two zeroes, thus no character code contains two adiacent zeroes.
PSK31 was designed for keyboard to keyboard communication, over long distances, with interferences and deep signal fading. Even without an active error control method, such as in AMTOR or PACTOR, the Viterbi decoding (in QPSK) can correct many errors while receiving.
The PSK31 method has quickly become very popular among radio amateurs worldwide, because the very narrow band it uses (less than 160 Hz) and its coding, yield a signal to noise ratio even better than that of Morse code transmission (CW).

The simpler way to use PSK31 is to connect a computer with a sound card to a radio and then use one of the many programs available, also on the software page on this site.

**Varicode ASCII coding**
Code or Ascii char.	Bit sequence	Code or Ascii char.	Bit sequence
0	1010101011	1	1011011011
2	1011101101	3	1101110111
4	1011101011	5	1101011111
6	1011101111	7	1011111101
8	1011111111	9	11101111
line feed	11101	11	1101101111
12	1011011101	return	11111
14	1101110101	15	1110101011
16	1011110111	17	1011110101
18	1110101101	19	1110101111
20	1101011011	21	1101101011
22	1101101101	23	1101010111
24	1101111011	25	1101111101
26	1110110111	27	1101010101
28	1101011101	29	1110111011
30	1011111011	31	1101111111
space	1	!	111111111
"	101011111	#	111110101
$	111011011	%	1011010101
&	1010111011	'	101111111
(	11111011	)	11110111
*	101101111	+	111011111
,	1110101	-	110101
.	1010111	/	110101111
0	10110111	1	10111101
2	11101101	3	11111111
4	101110111	5	101011011
6	101101011	7	110101101
8	110101011	9	110110111
:	11110101	;	110111101
<	111101101	=	1010101
>	111010111	?	1010101111
@	1010111101	A	1111101
B	11101011	C	10101101
D	10110101	E	1110111
F	11011011	G	11111101
H	101010101	I	1111111
J	111111101	K	101111101
L	11010111	M	10111011
N	11011101	O	10101011
P	11010101	Q	111011101
R	10101111	S	1101111
T	1101101	U	101010111
V	110110101	W	101011101
X	101110101	Y	101111011
Z	1010101101	[	111110111
\	111101111	]	111111011
^	1010111111	_	101101101
`	1011011111	a	1011
b	1011111	c	101111
d	101101	e	11
f	111101	g	1011011
h	101011	i	1101
j	111101011	k	10111111
l	11011	m	111011
n	1111	o	111
p	111111	q	110111111
r	10101	s	10111
t	101	u	110111
v	1111011	w	1101011
x	11011111	y	1011101
z	111010101	{	1010110111
\|	110111011	}	1010110101
~	1011010111	127	1110110101

**Convolutional Viterbi 5 bits code**
Bits	Shift	Bits	Shift	Bits	Shift	Bits	Shift
00000	180°	00001	+90°	00010	-90°	00011	0
00100	-90°	00101	0	00110	180°	00111	+90°
01000	0	01001	-90°	01010	+90°	01011	180°
01100	+90°	01101	180°	01110	0	01111	-90°
10000	+90°	10001	180°	10010	0	10011	-90°
10100	0	10101	-90°	10110	+90°	10111	180°
11000	-90°	11001	0	11010	180°	11011	+90°
11100	180°	11101	+90°	11110	-90°	11111	0

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PSK31

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