thumb|200px|right|A [[Spectrogram|waterfall display depicting several PSK31 transmissions at around 14.07 MHz. The green lines indicate a station that is transmitting.]]
<!-- image set to 300px to ensure its visible, allowed by WP:STYLE -->
PSK31 or "Phase Shift Keying, 31 Baud", also BPSK31 and QPSK31, is a popular computer-sound card-generated radioteletype mode, used primarily by amateur radio operators to conduct real-time keyboard-to-keyboard chat, most often using frequencies in the high frequency amateur radio bands (shortwave). PSK31 is distinguished from other digital modes in that it is specifically tuned to have a data rate close to typing speed, and has an extremely narrow bandwidth, allowing many conversations in the same bandwidth as a single voice channel. This narrow bandwidth makes better use of the radio frequency (RF) energy in a very narrow space thus allowing relatively low-power equipment (5 watts) to communicate globally using the same skywave propagation used by shortwave radio stations.
The International Telecommunication Union designates this type of emission as 60H0J2B, often abbreviated as J2B.
History
PSK31 was developed and named by English amateur radio operator Peter Martinez (call sign G3PLX) and introduced to the wider amateur radio community in December 1998.
The 31 baud BPSK modulation system used in PSK31 was introduced by Pawel Jalocha (SP9VRC) in his SLOWBPSK program written for Motorola's EVM radio. Instead of the traditional frequency-shift keying, the information is transmitted by patterns of polarity-reversals (sometimes called 180-degree phase shifts). PSK31 was enthusiastically received, and its usage spread rapidly 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 installation of large antenna systems, the use of high power, or both.
Use and implementation
A PSK31 operator typically uses a single-sideband (SSB) transceiver connected to the sound card of a computer running PSK31 software. When the operator enters a message for transmission, the software produces an audio tone that sounds, to the human ear, like a continuous whistle with a slight warble. This sound is then fed through either a microphone jack (using an intermediate resistive attenuator to reduce the sound card's output power to microphone levels) or an auxiliary connection into the transceiver, from which it is transmitted.
From the perspective of the transmitter, the sound 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 audio whistle received from the transceiver's headphone output is fed into a computer sound card's audio input, and software decodes it. The software displays the decoded text.
As shown in the figure, a cosine filter is used to smooth the rise and fall times of the audio waveform and eliminate key clicks. All subsequent amplification of the signal must be linear to preserve the modulation waveform and ensure minimum occupied bandwidth. In practice, this means limiting the transmit audio volume to below the level where the transmitter generates Automatic Level Control (ALC) feedback and disabling any audio compression or speech processing.
The Varicode is a kind of Fibonacci code where the boundaries between character codes are marked by two or more consecutive zeros. Like all Fibonacci codes, since no character code contains more than one consecutive zero, the software can easily identify the spaces between characters, regardless of the length of the character. The idle sequence, sent when an operator is not typing, is a continuous sequence of phase-shifts, which do not print on the screen.
|-
! Frequency
! Amateur Band
|-
| 1.838 MHz
| 160 meter
|-
| 3.580 MHz
| 80 meter
|-
| 7.035 MHz*
| 40 meter (region 3)
|-
| 7.040 MHz*
| 40 meter (regions 1)
|-
| 7.070 MHz*
| 40 meter (regions 2)
|-
| 10.142 MHz
| 30 meter
|-
| 14.070 MHz
| 20 meter
|-
| 18.097 MHz**
| 17 meter
|-
| 21.080 MHz*
| 15 meter
|-
| 24.920 MHz
| 12 meter
|-
| 28.120 MHz
| 10 meter
|-
| 50.290 MHz
| 6 meter
|-
| 144.144 MHz
| 2 meter
|-
| 222.07 MHz
| 1.25 meter
|-
| 432.2 MHz
| 70 centimeter
|-
| 909 MHz
| 33 centimeter
|}
<nowiki>*</nowiki> Current usage as of 2010, based on observation, is centered on 7,070.15 and 21,070.15. 7,035.15 is commonly used in Region 2 as of 2012. There is no authoritative list, as the frequencies are determined by common convention.
<nowiki>**</nowiki> PSK has moved from 18.100 to 18.097 due to FT8 use of the 18.100 frequency as of November, 2019.
The IARU Region 1 Bandplan was revised in March 2009 to reflect the expanded 40 meter band. The CW-only section within Europe, Africa, the Middle East and the former USSR is now 7.000 to 7.040. Region 2 - The Americas - followed in September 2013. Region 3 - South Asia and Australasia - has not yet synchronised its bandplan with Regions 1 and 2.
References
Further reading
- Martinez, Peter. PSK31: A new radio-teletype mode with a traditional philosophy (PDF) (November 1998). <!-- date per p. 10 of pdf --> <!--accessed 14 May 2008-->
- <cite id=qst>Meltz, Steve "The New HF Digital Modes - PSK31", QST, April, 1999, pp. 50-51 <!--accessed June 28, 2008--></cite>
- <cite id=radcom>Martinez, Peter. [http://www.arrl.org/tis/info/pdf/x9907003.pdf] "PSK31: A New Radio-Teletype Mode". RadCom, December 1998, updated February 1999<!--accessed July 1, 2008--></cite>
External links
- The "Official" PSK31 Page
- PSK31 Setup and Operation | a PSK31 guide
- PSK31 email discussion list with contests, app reviews, and more