PSK31 or "Phase Shift Keying, 31 Baud" is a digital radio modulation mode, used primarily in the amateur radio field to conduct real-time keyboard-to-keyboard informal text chat between amateur radio operators.
PSK31 was enthusiastically received, and its usage grew like wildfire worldwide lending a new popularity and tone to the on-air conduct of digital communications. Due to the efficiency of the mode, it became, and still remains, especially popular with operators whose circumstances do not permit the erection of large antenna systems and/or the use of high power.
A PSK31 operator typically uses a single sideband transceiver connected to the sound card of the PC. When the operator enters a message for transmission, the software produces an audio tone which sounds, to the human ear, like a continuous whistle with a slight warble. This is then fed through either a microphone jack (using an intermediate resistor to reduce the sound card's output power to microphone levels) or an auxiliary connection into the transceiver, where it is transmitted.
From the perspective of the transmitter, this amounts to little more than somebody whistling into the microphone. However, the software rapidly shifts the phase of the audio signal between two states (hence the name "phase-shift keying"), forming the character codes. These phase shifts serve the same function as the two tones used in traditional RTTY and similar systems.
To decode PSK31, the received audio whistle from the transceiver's headphone output is fed into the sound card's audio input, and the software decodes it. The software also includes a user interface on the PC, which is used to display the decoded text and manage the software configuration. The idle sequence is a continuous sequence of zeros, since no varicode word may contain two adjacent zeros, which results in a continuous reversals of phase as in BPSK.
PSK31 works well with propagation paths that preserve phase, and can be adversely affected by those that do not, such as transpolar paths, where auroral influence can disrupt the signal phase continuity.
Some software supports PSK10 and PSK05 variants, running at 10 baud and 5 baud, respectively. These slower speeds sacrifice throughput to provide even greater resistance to noise and other interference.
PSK31's bandwidth of 31.25 Hz was chosen because a normal typing speed of about 50 words per minute requires a bit rate of about 32 bits per second, and specifically because 31.25 Hz could easily be derived from the 8 kHz sample rate used in many DSP systems, including those used in the 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).
Colloquial usage of the term 'PSK31' in amateur radio usually implies the use of the most commonly used variant of PSK31: binary phase shift keying. BPSK uses no error control, but an allied mode, QPSK31, uses four phases instead of two, to provide a degree of forward error correction. It is very simple to switch from BPSK to QPSK if difficulties arise during a contact.
+ PSK31 Frequencies | |
! Frequency | amateur radio frequency allocations>Amateur Band |
1.838 MHz | 160 meters |
3.580 MHz | 80 meters |
*7.040 MHz | 40 meters (International_Amateur_Radio_Union#Regional_organisation |
*7.080 MHz | [[40 meters (International_Amateur_Radio_Union#Regional_organisation |
10.142 MHz | [[30 meters |
14.070 MHz | 20 meters |
18.100 MHz | 17 meters |
*21.080 MHz | 15 meters |
24.920 MHz | 12 meters |
28.120 MHz | 10 meters |
50.290 MHz | 6 meters |
Category:Quantized radio modulation modes Category:Packet radio
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