WEFAX reception: weather charts by radio
WEFAX reception for radio amateurs and listeners: with a shortwave receiver or an SDR and free software you receive the weather charts broadcast by radio for ships. Calculate the frequency to set and find the stations receivable from Italy.
Frequency to set in USB
Published frequencies are the assigned ones: to receive in USB you tune 1.9 kHz lower, so the signal sits around 1900 Hz in the audio, where decoding software looks for it.
Formula: USB frequency = published frequency − 1.9 kHz
Stations receivable from Italy
From the official NOAA document “Worldwide Marine Radiofacsimile Broadcast Schedules” (7 March 2025 edition). The date shows when the station last updated its data: for the times of each chart always use the official schedule.
Deutscher Wetterdienst — Hamburg/Pinneberg
| Callsign | Frequency (kHz) | USB (kHz) | UTC hours |
|---|---|---|---|
| DDH3 | 3855 | 3853.1 | see schedule |
| DDK3 | 7880 | 7878.1 | see schedule |
| DDK6 | 13882.5 | 13880.6 | see schedule |
Northwood (JOMOC) — GYA
| Callsign | Frequency (kHz) | USB (kHz) | UTC hours |
|---|---|---|---|
| GYA | 2618.5 | 2616.6 | 2200–0500 |
| GYA | 4610 | 4608.1 | 24 h |
| GYA | 8040 | 8038.1 | 24 h (alt.) |
| GYA | 11086.5 | 11084.6 | 0600–2000 |
Athens — SVJ4 old data: to be checked
| Callsign | Frequency (kHz) | USB (kHz) | UTC hours |
|---|---|---|---|
| SVJ4 | 4481 (carrier) | 4481 | see schedule |
| SVJ4 | 8105 (carrier) | 8105 | see schedule |
Parameters: 120 RPM, IOC 576 (shown as “120/576” in the NOAA document). NOAA ↗
How WEFAX reception works
WEFAX (radiofax) is an analogue system created for ships: weather services broadcast weather charts on shortwave that anyone can receive and decode with a computer.
What you receive
Black and white charts: surface pressure analysis, 24–96 hour forecasts, sea state and wave height, sometimes satellite images. Each station follows a fixed schedule published by the weather service.
What the signal looks like
The audio tone changes frequency with the shade of each point: centre 1900 Hz, white 400 Hz higher (2300 Hz), black 400 Hz lower (1500 Hz), greys in between. DWD uses a slightly wider shift, ±425 Hz.
How the image is built
The standard is 120 lines per minute, that is two lines per second, with index of cooperation (IOC) 576 setting the image proportions. A chart of about 1300 lines therefore takes around ten minutes.
Automatic start and stop
Each chart starts with a 300 Hz start tone for 5 seconds and 30 seconds of phasing signal, which aligns the image edge. It ends with a 450 Hz stop tone for 5 seconds followed by 10 seconds of black: fldigi detects them by itself.
WEFAX reception, step by step
A radio with USB or an SDR connected to the computer is enough; alternatively a shortwave web receiver.
Choose frequency and time
Use the calculator for the USB frequency and the official schedule to know when the chart you want is sent. Higher frequencies work better by day, lower ones at night.
Set up the radio
USB mode, filter at least 2.4 kHz wide, slow or off AGC, no noise reduction: it alters the tones and spoils the image.
Connect the audio to the computer
Audio cable or the radio’s USB sound card; with an SDR a virtual audio cable between the SDR program and the decoder is enough.
Set up fldigi
WEFAX mode with IOC 576; audio centre 1900 Hz; shift 850 Hz for DWD. Enable automatic start: the program detects the start and stop tones and aligns the image with the phasing signal.
Wait for the start and save
The image builds line by line, about two per second. fldigi saves it as PNG automatically when the transmission ends.
Common problems
Slanted image
The sound card clock is not exactly 48 or 11.025 kHz: correct it once with the program’s “Tilt”/slant adjustment.
Negative or garbled image
Wrong sideband (LSB instead of USB) or wrong frequency: check you are in USB, 1.9 kHz below the published frequency.
Image shifted sideways
The program started without the phasing signal: use automatic alignment or shift the image by hand.
It does not start by itself
Signal too weak or start tone missed: start manually and try another frequency of the same station.
Scattered white or black lines
Noise or fading: normal on shortwave. Try the frequency best suited to the time of day or a web receiver closer to the station.
Sources: NOAA NWS — Worldwide Marine Radiofacsimile Broadcast Schedules (7 March 2025, PDF), fldigi — WEFAX, Bureau of Meteorology — Technical characteristics of voice and fax HF transmissions, OARC wiki — DWD WEFAX, Deutscher Wetterdienst — shipping. Sources consulted on 18 October 2026. Links open on the publisher’s website. Times and frequencies can change: the station’s official schedule prevails.
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