Frank's Ham Radio Radio page

PSK31 stands for "Phase Shift Keying, 31 Baud". It was introduced by SP9VRC in his SLOWBPSK program, and later reworked by Peter Martinez, G3PLX. Instead of the traditional frequency-shift keying (FSK), the information is transmitted by patterns of phase shifts). Characters are represented with variable-length encoding (Huffman code). Bandwidth (splatter) of the output signals is minimized by cosine-shaping the envelope of the transmitted bits. The PSK signal spectrum comprises two pure tones, at ±15 Hz (not kHz!) from the center frequency (actually 8 kHz divided by 512 = 15.125 Hz). The 31 baud speed was chosen based on an the keyboard-typing speed of the average ham operator. Because of the narrow bandwidth, transmitter and receiver frequency stability is important. PSK31 offers weak-signal performance that rivals that of CW, but achieves this without the need for synchronization or handshaking protocols.

There are two basic PSK31 modes: Binary PSK (BPSK) and Quadrature PSK (QPSK). BPSK uses 180 degree phase shifts ("polarity reversals"), whereas QPSK uses two pairs of phase shifts (0 and 180, 90 and 270 degree). QPSK can be thought of as two BPSK signals on the same frequency, but 90 degrees out of phase, and with only half the transmit power in each. That is: twice the data transmission bandwidth, at the cost of a 3 dB reduction in the Signal to Noise ratio. QPSK uses the extra bandwidth for Forward Error Correction (FEC). This FEC is based on Viterbi coding, that is configured to keep track of its "guesses' for the 20 most recent received/decoded characters, as well as phase shift matching. A "predictor-regrettor" scheme. This processing introduces 640 msec ( = 20 bits) additional (but acceptable) lag in the receiver chain.

audio spectrum with multiple PSK31 signals

Articles:

	"PSK31: A New Radio-Teletype Mode", by Peter Martinez - G3PLX, QEX July/Aug 1999, pp. 3-9
	The "New" HF Digital Modes-PSK31 by Steve, N2QLQ, QST April 1999, pp. 50-51

Links:

	PSK31 "Official" Home Page is here
	PSK31 fundamentals by Peter Martinez - G3PLX,
	Getting Started on the PSK31 Mode by Richard Griffin, NB6Z

	Click here for a description of how I hook up my PC to my radio; here and here are some more audio (and CAT) interfaces.
	Click here to hear what a BPSK signal sounds like (can be used to try out the software).

Regular PSK activity can be found on these amateur radio frequencies:

These recommended frequencies are in accordance with the IARU bandplan for region 1. There may be differences for regions 2 and 3

1838.150 kHz
3580.150 kHz
7035.15 kHz for region 1 and region 3, and 7080.15 for region 2 *
10142.150 kHz
14070.150 kHz
18100.150 kHz
21080.150 kHz (although most activity can be found 10 kHz lower)
24920.150 kHz
28120.150kHz

PSK31 activity starts from the bottom edge of the IARU RTTY bandplan, expanding upwards as activity increases.