PSK31
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PSK31 or "Phase Shift Keying, 31 Baud" is a digital mode of radio communication, used primarily in the amateur radio service. It is usually used to transmit relatively short text messages between two radio operators.
Use and Implementations
In practice, PSK31 is usually used to exchange relatively short, conversation style messages between two radio operatiors. PSK31 is a half-duplex mode of communication. Thus only one participant in the conversation can send a message at any given time. PSK31 can often overcome interference where other voice or data methods of communicaion fail. However, due to its relatively slow speed and lack of error checking, PSK31 is not well suited for the transmission of large blocks of data. The mode works well with propagation paths that preserve phase, but poorly for those that do not, such as polar paths.
PSK31 mode was developed by English amateur radio operator Peter Martinez (G3PLX). Martinez initially called his creation "varicode", because it uses variable length encodings to represent characters. Technically, varicode is the encoding, and PSK31 the transmitting method. Varicode was designed so that the more frequently occurring characters had shorter encodings and the rarer characters used the longer encodings, a coding scheme similar to Morse code. The radio operator uses computer software to generate and decode an audio signal containing the encodings; the encoded audio signal is used to modulate the RF carrier of a transmitter.
Technical Information
PSK31 audio bandwidth is very narrow (31.25 Hz), making it highly suitable for low power and crowded band operation. The 31.25 Hz bandwidth was chosen because transmitting Varicode at a normal typing speed of about 50 words per minute needs a bit-rate of about 32 per second. The bit-rate of 31.25 was chosen because it could easily be derived from the 8 kHz sample-rate used in many DSP systems such as those used in computer sound cards commonly used for PSK31 operation: 31.25 Hz is 8 kHz divided by 256, and so can be derived from 8 kHz by halving the frequency eight times.
External link
- PSK31 Info Page (http://www.psk31.com) – Provides information and links to software implementations