The BPSK31 and QPSK31 modes are designed to assure communications with Signal-to-Noise ratio down to 0.1 (-11.5 dB, for a PC at 166 MHz or more). The speed is 37 wpm in capital letters and 51 wpm in small letters. When we say  PSK31, it refers to a general term for BPSK31 and QPSK31. The convolutional encoding of QPSK31 allows it to lower the number of errors.


    This mode is included into the software MULTIPSK by Patrick F6CTE, there is the description of this mode and its variants as well as the specifications coming from his software :

Created by: Peter Martinez G3PLX
Description :
Baud rate : 31.25
Speed : 37 wpm in capital letters and 51 wpm in small letters (average)
Modulation : DBPSK
Receive mode: indifferent (LSB or USB) for BPSK31 only, for QPSK31 USB is mandatory
Character set : ASCII characters + ANSI extended characters + an error reset character  («
 Varicode » characters)
Shape of pulse : raised cosine
Bandwidth : about 80 Hz,
Demodulation : coherent,
Synchronization : automatic using the signal
Correction code : no
Convolution code : no for BPSK31, yes for QPSK31 (Rate=1/2, Constraint length=5, use of Viterbi decoder with soft decison)
Interleaving : no
Automatic Frequency Correction : about +/- 10 Hz depending on signal-to-noise ratio,
Drift tolerance : 60 Hz/min in BPSK31 and 20 Hz/min in QPSK31 (depending on level)
Pmean/Ppeak : 0.79 for BPSK31 and 0.35 for QPSK31
Lowest S/N : -11.5 dB
Waterfall range : 200 to 4300 Hz for Multipsk
Note : the BPSK31 mode is very much used, QPSK31 is not used that much.

Recommanded frequencies for BPSK31 or QPSK31 (USB) in kHz
1838, 3580, 7035, 10140, 14070, 18100, 21080, 24920, 28070, 28120, 50000, 144000 (144605 in France and 144144 in Italy).