WSPR (amateur radio software)

The type of radio emission is “F1D”, frequency-shift keying. 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 bits (binary digits). These are encoded using a convolutional code with constraint length K = 32 and a rate of r = {{frac|1|2}}.{{Cite web|url=http://www.g4jnt.com/Coding/WSPR_Coding_Process.pdf|title=G4JNT: The WSPR Coding Process: Non-normative specification of WSPR protocol}} The long constraint length makes undetected decoding errors less probable, at the cost that the highly efficient Viterbi algorithm must be replaced by a simple sequential algorithm for the decoding process.

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 = {{frac|1|2}}.

• Number of binary channel symbols:

:nsym = (50 + K − 1) × 2 = 162.

• Keying rate is {{frac|12000|8192}} = 1.4648 baud.
• Modulation is continuous phase 4 FSK, with 1.4648 Hz tone separation.

File:4-FSK used for WSPR.jpg

• 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 × {{frac|8192|12000}} = 110.6 s.
• Transmissions nominally start one second into an even UTC 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).

File:WsprryPi.JPG

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,WSPR Beacon with Si 570 and Atmel AVR http://wsprnet.org/drupal/sites/wsprnet.org/files/si570wspr.pdf or Si 5351.QRSS/WSPR Transmitter Kit https://qrp-labs.com/ The Raspberry Pi can also be used as WSPR beacon.File:WSPR 2014.svg

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

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 on 8 March 2014.[https://www.abc.net.au/news/2021-05-05/malaysia-airlines-mh370-series-of-turns-before-disappearing/100116446 Malaysia Airlines flight MH370 left 'false trails' before disappearing, new research suggests], Anne Barker, ABC News Online, 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 {{convert|150|nmi}} from the coast of Sumatra before vanishing, later proposing a search area centered around {{coord|33.177|S|95.3|E}}.{{Cite news|last=Browning|first=Simon|date=3 December 2021|title=MH370: Could missing Malaysian Airlines plane finally be found?|work=BBC|url=https://www.bbc.com/news/business-59517821|access-date=27 January 2022}}{{Cite web |last=Thomas |first=Geoffrey |date=2021-09-07 |title=Breakthrough technology giving real hope for a new search for MH370 |url=https://www.airlineratings.com/news/breakthrough-technology-giving-real-hope-for-a-new-search-for-mh370/ |access-date=2023-05-16 |website=Airline Ratings |language=en-AU}}{{Cite web |last=Thomas |first=Geoffrey |date=2022-06-25 |title=MH370 TRACKING EXPERT DEMONSTRATES HIS TECHNOLOGY ONCE AGAIN |url=https://www.airlineratings.com/news/industry-news/mh370-tracking-expert-demonstrates-technology/ |access-date=2023-05-16 |website=Airline Ratings |language=en-AU}}{{Cite web |last=Thomas |first=Geoffrey |date=2022-10-28 |title=MH370: New Research Paper Confirms WSPRnet Tracking Technology |url=https://www.airlineratings.com/news/mh370-new-research-paper-confirms-wsprnet-tracking-technology/ |access-date=2023-05-16 |website=Airline Ratings |language=en-AU}}

{{As of|March 2024}}, the validity of Godfrey's claim is yet to be established.{{Cite web |last=Thomas |first=Geoffrey |date=2022-11-02 |title=MH370 New Location Critics Sunk |url=https://www.airlineratings.com/news/critics-of-wsprnet-tracking-mh370-been-answered/ |access-date=2023-05-16 |website=Airline Ratings |language=en-AU}}

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, 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.{{Cite web|url=https://www.bbc.co.uk/iplayer/episode/m001x0yh/why-planes-vanish-the-hunt-for-mh370|title=Why Planes Vanish: The Hunt for MH370|via=www.bbc.co.uk}}{{cite news |url=https://www.independent.co.uk/travel/news-and-advice/mh370-radio-signals-theory-bbc-doc-b2508628.html |title=Could disrupted radio signals locate MH370? Theory is examined in new documentary |last=Wilson |first=Natalie |work=The Independent |date=7 March 2024 |access-date=8 March 2024}} However, by April 2025 Maskell had not yet published such results.{{Cite web | url=https://www.liverpool.ac.uk/people/simon-maskell/publications |title=Professor Simon Maskell Publications |access-date=2025-04-14}}{{fv|reason=Absence of evidence is not evidence of absence|date=April 2025}}

WSPR was originally released in 2008.

{{Reflist}}

• {{Official website}}
• [http://wsprnet.org Central database of reception reports]
• [https://wspr.live/ Live WSPR propagation analysis]

[https://www.dropbox.com/s/k4fn8eec4z9np0z/GDTAAA%20WSPRnet%20MH370%20Analysis%20Flight%20Path%20Report.pdf GDTAAA WSPRnet MH370 Analysis Flight Path Report] (Self-published, Dropbox){{Digital_modes|state=collapsed}}

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