This mode handles the PSK31 mode, which has recently started to gain interest in the amateur community. This mode is ideal for conversations, as it supports effective rates of around 50 wpm.
PSK31 is sort of a cross between CW and RTTY. Data is transmitted at 31.25 baud (hence the name). A tone (typically 1000 Hz) is continuously transmitted, and the phase is inverted if the next bit is a zero. This produces a distinctive trilling sound, somewhat like a treefrog.
However, unlike RTTY, and much like CW, the length of each character varies, from a minimum of one bit(for a space) to a maximum of ten bits (for seldom used characters). Two zero bits are sent between characters. When no data is being sent (idle), continuous zero bits are transmitted, so there are phase reversals 31 times per second, meaning there is always a signal to lock onto.
Correct receiver tuning is extremely critical for sucessful PSK31 reception. A tuning error of 20 Hz can cause poor or no reception! The following shows a correctly tuned PSK31 mode signal:
 
This is the demodulated signal. Any portion below the red line is a zero bit, above the red line is a one bit. During idle transmission mode, all of the demodulated data will be below the red line.
Suggested frequencies for PSK31 operation are:
1838.150
3580.150
7035.150
10140.150
14070.150
18100.150
21080.150
24920.150
28120.150
The "Official PSK31 Homepage" is located at: http://www.kender.es/~edu/psk31.html
