| 
| 
PSK31 Intro and Theory
_________________________________________________________
PSK31 is based on an idea by SP9VRC and developed by Peter Martinez, G3PLX, who also developed AMTOR. Based on RTTY, PSK is used for live keyboard-to-keyboard QSOs at 50 WPM (31 Baud) and uses "Phase Shift Keying" to signal mark and space values, instead of changing the frequency.
DSP is used to change the phase by 180 degrees when a switch from mark to space is needed. DSP analysis by the program instantly detects this "Phase Shift".
PSK works in a very narrow bandwidth, which sharply reduces noise and QRM. This narrow signal also makes it an excellent QRP (low power) mode, with between 5 and 10 watts producing excellent inter-continental paths in some cases.
The front-end DSP filter and pulse shaping keep the waveform compact, approximately 40 Hz at -3dB and 80 Hz at -40 dB. Pulse shaping uses a raised cosine to ramp amplitude during phase transitions and leaves the amplitude at full value during no phase reversals.
PSK31 uses much less bandwidth than traditional digital modes.
PSK31's two modes: BPSK and QPSK
In the QPSK mode, instead of just keying by phase reversals, or 180-degree phase-shifts, an additional pair of 90 and 270-degree phase-shifts are possible.
If you think of BPSK as reversing the polarity of the signal, then QPSK can be thought of as two BPSK signals on the same frequency, but 90 degrees out of phase with each other, and with only half the power in each.
The extra speed in QPSK is used for error correction. This works well under most conditions. Certain noisy conditions, and weaker signals, can benefit from the full power (single signal) of the QPSK mode.
Visit the PSK31 Official Home Page at:
http://aintel.bi.ehu.es/psk31.html
Note: Because this is commercial software, Peter Martenez, G3PLX's Introduction and Theory of PSK31 cannot be included as part of these help files, but these really should be reviewed for a better understanding of PSK and its development. Peter Martenez's outline and theory of PSK31 can be viewed on the website of MixW beta tester and help file contributor, RICHARD B. GRIFFIN, NB6Z at the following link: http://www.teleport.com/~nb6z/psk31.htm
MixW has full BPSK31 and QPSK31 capabilities, but Nick did not use the G3PLX source code to implement it. By using his own source code, Nick is in keeping with Peter's guidelines for the use of PSK31 in commercial software.
We are very grateful to Peter for PSK31, a great gift to the radio art.