First things first; my first confirmed DX QSO in PSK31 mode was from om Nestor from Buenos Aires. The QSO was made 22 June 2004 on the 15 meter band (QRG was 21.082 MHz). Not that special one should say. But if you take into account the circumstances ( 20 Watt HF power and a simple dipole aerial -inverted V- under the roof) one might be slightly amazed . My signal arrived with a solid S599 in Argentinia. For experienced HAM radio amateurs, having worked with PSK31 for a longer period, nothing to be amazed of. For me, however, it was a small miracle that - although assisted by that great mirror above us (free electrons in the ionosphere) - the tiny PSK signals could cross the Atlantic Ocean without problems.

Simulations show that PSK31 is a real QRP mode. The program NTIA/ITS for example shows the incredible opportunities of PSK31; below is shown what your chances were for making PSK31 QSOs with only 5 Watts (!) in the 40 m band on February 2001 around 16 uur UTC. The PSK31 transceiver " under test " was located in Germany. As you can see, the chance for making a QRP-link within Europe was 90% (red area). Parts of Australia, New Zealand and the Pacific could be reached with some extra luck (yellow areas; 75%) ! This kind of pictures made me very curious. The proper time to collect some background information about this interesting mode and get things prepared to go QRV with PSK31 !

PSK31 is a - from RTTY derived - modus being developed in 1999 by Peter Martinez, G3PLX. PSK means Phase Shift Keying. Where other modes switch on- and off the carrier wave (CW), vary the carrier wave frequency (FM), or shift the carrier wave (FSK), PSK31 does not spoil valuable HF power because of its smart principle. BPSK (Binary Phase Shift Keying) is being generated by changing the polarity of the carrier wave. This happens with a ' keying rate ' of 31.25 baud. Therefore, theoratically the bandwidth of the BPSK31 signal will be 31.25 Hz (!). In order to facilitate 'life QSO's' this choosen bitrate turns out to be the practical minimum value. This bandwidth is much smaller than the bandwidths for any other mode of telegraphy (digimode). The fast click created by the polarity change results in a relative wide frequency spectrum. Therefore, the signal must be filtered to the proper bandwidth. After this filtering process, a double side band (DSB) signal with suppressed carrier ("two tone signal") comes available. The RTTY signal is also a two tone signal with a greater frequency separation compared to the PSK31 signal.

The efficient PSK31 signal  shown as graph

In addition to the 31.25 Hz bandwidth, the use of the Varicode is a second characteristic of this modus. The code was developed by Peter Martinez. In fact, it is based on the old morsecode but some enhancements were added. The signlength of the characters is variable (as in the morsecode). The average signlength is 6.5 bits per sign. The Varicode alfabeth was derived by Peter from a huge pile of English texts. The often used character ' e ' has the code 11 (short !). The less often used [ sign has the code 111110111. Useful to know for practice; as a result of the construction of the Varicode alfabeth, the transmission rate for the small characters (non-capitals) is twice the rate of the capitals. In order to transmit Varicode at a speed of about 50 words per minute, a bitrate of appr. 32 bits per seconde is required. The value of 31.25 was choosen because this is an easy value to derive from the 8 KHz sampling signal of DSP systems. Practice has shown that 31.25 Hz is an acceptable bandwidth to facilitate ' life QSO' s ' ("chatting").

PSK31 signals can often be received on following frequencies (not accepted in the official band plans for 2004):

A related mode to BPSK31 is QPSK31 (Quaternary Phase Shift Keying). Compared to the BPSK31 signal, QPSK31 has a doubled information capacity without the disadvantage of a double bandwidth and loss of speed. A second carrier wave (shifted in phase) is added. The price that must be paid is the fact that the available HF power must be divided amongst both channels. Practice has also shown that QPSK frequency stability must be twice as good compared to PSK31 (QPSK within 4 Hz). For the old transceivers no option ! Two stations often start to work with BPSK and switch to QPSK, if the conditions allow it.

The designer has refrained from adding an error correcting algoritm into the PSK31 modus (as in e.g. the PACTOR modus). This algoritm should slow the transmissions thus spoiling the possibility of life two-way contacts. 'Breaking-in' , as commonly done in ' live QSO's ' , should become impossible as well.

MixW also provides a built-in Logbook. Very handy. The number of succesful QSO's is counted automatically. It also tells you whether you have workend with a station before. In addition, the macros allow the possibility to program standard texts. In the example here, under the "CQ CQ"-button the user has programmed the text shown in the RX screen (upper screen) in red and the same text is visible in black in the TX screen. Very useful that items like UTC, callsign counterstation and Log # can be integrated into the macros. The "BYE"- button for example can generate a piece of text with the current date, UTC and Log # . Very nice. Also for your counter station. Do not forget to align your cursor behind the last character in the TX screen, otherwise your transmission will stop somewhere in the middle of a sentence (the actual position of the cursor). I have experienced this some times.

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