Field Guide · protocol

Also known as: WSPR

WSPR (Weak Signal Propagation Reporter, pronounced “whisper”) is an amateur-radio beacon mode built not to hold conversations but to map which radio paths are open. Stations transmit a tiny fixed message — callsign, grid locator, and transmit power — using very slow 4-tone FSK, and receivers worldwide upload every decode to a central database, turning the amateur bands into a live propagation sensor.1 Because the mode sacrifices data rate for sensitivity, WSPR signals of a few hundred milliwatts are routinely decoded across oceans.

beacon TX call·grid·dBm HF path RX / decode WSPRnet 4-FSK · 1.46 baud · rate-1/2 K=32 convolutional code
WSPR beacons a callsign, grid, and power; distant receivers decode and log spots to a global database, revealing open propagation paths.

Overview

A WSPR transmission is entirely automated. On even two-minute boundaries a station keys up for about 111 seconds, sending a 50-bit message spread across 162 slow tones. Receivers running the same software decode any signals in a 200 Hz window, extract the reported power, estimate the received SNR, and upload the result — with timestamps — to WSPRnet. The aggregate is a continuously updated worldwide map of band openings.

Technical characteristics

Property Value
Modulation 4-FSK, continuous-phase, ~1.46 Hz tone spacing
Symbol rate 1.4648 baud (162 symbols)
Occupied bandwidth ~6 Hz per signal
Slot length 2 min (110.6 s of tones)
Message payload 50 bits (28-bit call, 15-bit grid, 7-bit power)
FEC Constraint-length 32, rate-1/2 convolutional code
Threshold ≈ −28 dB SNR (2.5 kHz reference)

History

WSPR was released in 2008 by Joe Taylor (K1JT) as part of the WSJT family of weak-signal programs. Its convolutional-coded, ultra-narrow waveform pushed decoding several dB below what conversational modes could reach, and the paired WSPRnet reporting site made it a standard tool for propagation research. Much of the coding philosophy later informed conversational modes like FT8.2

Deployment

WSPR runs on the HF amateur bands (with dedicated 200 Hz windows such as 14.0956 MHz on 20 m) and increasingly on LF/MF and VHF. Purpose-built low-power beacons and networked receivers make it a widely cited source of real-time ionospheric-propagation data.

Decoding it with GopherTrunk

GopherTrunk does not decode WSPR — WSPR is an HF weak-signal beacon mode outside the scope of a trunked land-mobile scanner. It is received with an SSB-capable receiver or SDR feeding audio into WSJT-X or the dedicated WSPR software, with the PC clock locked to UTC; a stable, frequency-accurate front end matters because the signal is only a few hertz wide.

Sources

  1. WSPR (amateur radio software) — Wikipedia, for the beacon concept, 4-FSK waveform, message contents, and the WSPRnet reporting network. ↩

  2. WSPR User’s Guide — K1JT, the authoritative description of the WSPR protocol, timing, message coding, and operating procedure. ↩

See also