The Digital Domain of Amateur Radio

PSK31 - An HF Digital Mode

When you want to work the world, HF is a necessity. HF Digital usually has an advantage to HF voice, since it doesn't take nearly as much bandwidth to send a data packet as it does a voice. As a result, the signal can travel farther and still be clearly decoded by the receiving station.

Standard HF Packet modes (Pactor, Amtor) tend to run around 300 bits/sec, but those still require a somewhat large bandwidth, requiring more power to reach farther. But PSK31 uses only 31Hz of bandwidth - next to nothing, compared to the 1-2+ KHz of bandwidth commonly used in HF. Of course, PSK31 only works at 31 bits/second, but for casual conversations, PSK31 is more than sufficient, working at over 40 words per minute (assuming 8 bit characters, 5 characters per word).

So what makes PSK31 so much better than a simple mode like CW (morse code)? Up front, phase shifting has more advantages than CW. CW uses amplitude (on/off) keying. In a noisy or distorted propagation environment, the amplitude of a signal will shift and vary much more than the phase of a signal.