PSK31 is the abbreviation of Phase Shift Keying 31.25 Hz. PSK31 is an excellent digital modulation mode and just needs extremely narrow bandwidth. its transmission rate is always maintained at 31.25 bits per second, so it is called PSK31. It is mainly developed by the SP9VPC and G3PLX.
PSK31 not only occupies very little bandwidth but also has better performance when the transmission is weak with interfering. so it is a very excellent digital modulation mode. This feature is of great significance in today's severely interfering short-wave bands and is often used by many hams. PSK31 usually uses BPSK or 180-degree phase shift, but sometimes uses QPSK to work. Cosine envelope technology is used in the modulation process to effectively limit the harmonic bandwidth caused by the HARD-KEYING effect in PSK modulation. Due to the narrow bandwidth of PSK31, there is basically less mutual interference between stations. As for the unstable transmission, it is difficult to predict. Therefore, in fact, PSK31 communication is still based on BPSK. Usually, the communication parties find that the error rate is very high. Move to QPSK for communication. In addition, QPSK has to compare four phases, so the requirements for frequency stability are quite high.
There is much software of PSK31, such as digipan v1.6d, Droid PSK, HRD, and so on.