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:

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
01010101011 11011011011
21011101101 31101110111
41011101011 51101011111
61011101111 71011111101
81011111111 911101111
line feed11101 111101101111
121011011101 return11111
141101110101 151110101011
161011110111 171011110101
181110101101 191110101111
201101011011 211101101011
221101101101 231101010111
241101111011 251101111101
261110110111 271101010101
281101011101 291110111011
301011111011 311101111111
space1 !111111111
"101011111 #111110101
$111011011 %1011010101
&1010111011 '101111111
(11111011 )11110111
*101101111 +111011111
,1110101 -110101
.1010111 /110101111
010110111 110111101
211101101 311111111
4101110111 5101011011
6101101011 7110101101
8110101011 9110110111
:11110101 ;110111101
<111101101 =1010101
>111010111 ?1010101111
@1010111101 A1111101
B11101011 C10101101
D10110101 E1110111
F11011011 G11111101
H101010101 I1111111
J111111101 K101111101
L11010111 M10111011
N11011101 O10101011
P11010101 Q111011101
R10101111 S1101111
T1101101 U101010111
V110110101 W101011101
X101110101 Y101111011
Z1010101101 [111110111
\111101111 ]111111011
^1010111111 _101101101
`1011011111 a1011
b1011111 c101111
d101101 e11
f111101 g1011011
h101011 i1101
j111101011 k10111111
l11011 m111011
n1111 o111
p111111 q110111111
r10101 s10111
t101 u110111
v1111011 w1101011
x11011111 y1011101
z111010101 {1010110111
|110111011 }1010110101
~1011010111 1271110110101

Convolutional Viterbi 5 bits code
BitsShiftBitsShift BitsShiftBitsShift
00000180° 00001+90° 00010-90° 000110
00100-90° 001010 00110180° 00111+90°
010000 01001-90° 01010+90° 01011180°
01100+90° 01101180° 011100 01111-90°
10000+90° 10001180° 100100 10011-90°
101000 10101-90° 10110+90° 10111180°
11000-90° 110010 11010180° 11011+90°
11100180° 11101+90° 11110-90° 111110


The end of one of my PSK31 QSO, with the Slovenian station S57LWE.
The program I am using here is the RCKRtty and you can see also the waterfall,
where the effect of the 500 Hz filter is visually evident.
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