WSPR (pronounced "whisper") is an acronym for Weak Signal Propagation Reporter. It is a protocol, implemented in a computer program, used for weak-

signal A signal is both the process and the result of transmission of data over some media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processing, information theory and biology. In ...

radio communication Radio is the technology of telecommunication, communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transm ...

between

amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency radio spectrum, spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emer ...

operators Operator may refer to: Mathematics * A symbol indicating a mathematical operation * Logical operator or logical connective in mathematical logic * Operator (mathematics), mapping that acts on elements of a space to produce elements of another ...

. The protocol was designed, and a program written initially, by Joe Taylor, K1JT. The software code is now

open source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use and view the source code, design documents, or content of the product. The open source model is a decentrali ...

and is developed by a small team. The program is designed for sending and receiving low-power transmissions to test propagation paths on the MF and HF bands. WSPR implements a protocol designed for probing potential propagation paths with low-power transmissions. Transmissions carry a station's callsign, Maidenhead grid locator, and transmitter power in dBm. The program can decode signals with a

signal-to-noise ratio Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to noise power, often expressed in deci ...

as low as −28 dB in a 2.5 kHz bandwidth. Stations with internet access can automatically upload their reception reports to a central database called WSPRnet, which includes a mapping facility.

The WSPR Protocol

The type of radio emission is “F1D”,

frequency-shift keying Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is encoded on a carrier signal by periodically shifting the frequency of the carrier between several discrete frequencies. The technology is used fo ...

. A message contains a station's callsign, Maidenhead grid locator, and transmitter power in dBm.Joe Taylor, K1JT: WSPRing Around the World. QST November (2010), p. 30-32. The WSPR protocol compresses the information in the message into 50

bit The bit is the most basic unit of information in computing and digital communication. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represented as ...

s (binary digits). These are encoded using a

convolutional code In telecommunication, a convolutional code is a type of error-correcting code that generates parity symbols via the sliding application of a boolean polynomial function to a data stream. The sliding application represents the 'convolution' of th ...

with constraint length ''K'' = 32 and a rate of ''r'' = . The long constraint length makes undetected decoding errors less probable, at the cost that the highly efficient

Viterbi algorithm The Viterbi algorithm is a dynamic programming algorithm for obtaining the maximum a posteriori probability estimate of the most likely sequence of hidden states—called the Viterbi path—that results in a sequence of observed events. This i ...

must be replaced by a simple sequential algorithm for the decoding process.

Protocol specification

The standard message is + <4 character locator> + ; for example “K1ABC FN20 37” is a signal from station K1ABC in Maidenhead grid cell “FN20”, sending 37 dBm, or about 5.0 W (legal limit for 630 m). Messages with a compound callsign and/or 6 digit locator use a two-transmission sequence. The first transmission carries compound callsign and power level, or standard callsign, 4 digit locator, and power level; the second transmission carries a hashed callsign, 6 digit locator, and power level. Add-on prefixes can be up to three alphanumeric characters; add-on suffixes can be a single letter or one or two digits. * Fields of a standard message: :28 bits for callsign, :15 bits for locator, : 5 bits for power level, : 2 bits for message type, :total: 50 bits. * Forward error correction (FEC): :non-recursive convolutional code with constraint length ''K'' = 32, rate ''r'' = . * Number of binary channel symbols: :nsym = (50 + K − 1) × 2 = 162. * Keying rate is = 1.4648 baud. * Modulation is continuous phase 4 FSK, with 1.4648 Hz tone separation. 4-FSK used for WSPR

* Occupied bandwidth is about 6 Hz * Synchronization is via a 162 bit pseudo-random sync vector. * Each channel symbol conveys one sync bit (LSB) and one data bit (MSB). * Duration of transmission is 162 × = 110.6 s. * Transmissions nominally start one second into an even

UTC Coordinated Universal Time (UTC) is the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones. UTC facilitates international communica ...

minute: e.g., at hh:00:01, hh:02:01, etc. * Minimum S/N for reception is around –34 dB on the WSJT scale (2500 Hz reference bandwidth).

Applications

The protocol was designed to test propagation paths on the LF, MF and HF bands. Also used experimentally at VHF and higher frequencies. Other applications include antenna testing, frequency stability and frequency accuracy checking. Usually a WSPR station contains a computer and a transceiver, but it is also possible to build very simple beacon transmitters with little effort. For example a simple WSPR beacon can be built using the Si 570, or Si 5351. The

Raspberry Pi Raspberry Pi ( ) is a series of small single-board computers (SBCs) developed in the United Kingdom by the Raspberry Pi Foundation in collaboration with Broadcom Inc., Broadcom. To commercialize the product and support its growing demand, the ...

can also be used as WSPR beacon. WSPR 2014

An accurate clock is essential both for transmission and decoding of received signals.

MH370 hypothesis

In May 2021, aerospace engineer Richard Godfrey suggested examining historical WSPR data as a way to define the flight path of

Malaysia Airlines Flight 370 Malaysia Airlines Flight 370 (MH370/MAS370) was an international passenger flight operated by Malaysia Airlines that disappeared from radar on 8 March 2014, while flying from Kuala Lumpur International Airport in Malaysia to its planned de ...

on 8 March 2014.Malaysia Airlines flight MH370 left 'false trails' before disappearing, new research suggests
Anne Barker,

ABC News Online ABC News, also known as ABC News and Current Affairs, is a public news service produced by the Australian Broadcasting Corporation. The service covers both local and world affairs, broadcasting both nationally as ABC News, and across the Asia- ...

, 2021-05-05 In November 2021, Godfrey stated his belief that his analysis indicates the aircraft flew in circles for around 22 minutes in an area from the coast of

Sumatra Sumatra () is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the list of islands by area, sixth-largest island in the world at 482,286.55 km2 (182,812 mi. ...

before vanishing, later proposing a search area centered around . , the validity of Godfrey's claim was yet to be established. On 6 March 2024 the BBC documentary ''Why Planes Vanish: The Hunt for MH370'' examined Godfrey's claim and reported that Simon Maskell, a statistician at the

University of Liverpool The University of Liverpool (abbreviated UOL) is a Public university, public research university in Liverpool, England. Founded in 1881 as University College Liverpool, Victoria University (United Kingdom), Victoria University, it received Ro ...

, was undertaking an analytical study of the possibility of using WSPR technology to locate the missing aircraft. At the time of the BBC documentary, Maskell stated he would be releasing results from this study within six months. However, by April 2025 Maskell had not yet published such results.

The WSPR Protocol

Protocol specification

Applications

MH370 hypothesis

History

References

External links

Further reading