DWD weather fax from Pinneberg: weather charts on 7880 kHz

What you hear

To the ear, weather fax is a steady, slightly rasping tone with a rhythm inside it: one line every half second, 120 lines a minute, for about ten minutes per chart. Each transmission begins with a few seconds of a start tone, a kind of two-note siren that tells the receiver which format to expect, and ends with a stop tone; between charts there is silence or a bare carrier. The picture, once decoded, is a black-and-white chart: isobars across the North Atlantic, fronts, pressure centres with their values, the date and time of the analysis in a corner, the DWD's name on the frame.

The programme includes surface analyses several times a day, forecast charts for one to several days ahead, sea-state and wave charts, sea surface temperature and, in winter, ice charts for the Baltic. They are the same charts the marine weather office issues on paper and on the web; the radio version is for ships that have neither.

Who transmits and why

The Deutscher Wetterdienst runs the service from its transmitter site at Pinneberg, north-west of Hamburg, for ships in the North Sea, the Baltic and the North Atlantic. A chart received by radio needs no internet connection, no subscription and no satellite dish, only an HF receiver and a decoder, which is why fax has outlived most predictions of its end. The format is the standard marine one: 120 lines per minute, index of cooperation 576, frequency-modulated audio in which 1500 Hz is black and 2300 Hz is white.

Three frequencies carry the same programme: 3855 kHz for the night, 7880 kHz for day and night and 13882.5 kHz for the daytime. Those are the nominal, assigned frequencies; a receiver in upper sideband has to be tuned 1.9 kHz lower so that the black and white tones land where the decoder expects them, which is why the catalogue shows 7878.1 kHz as the dial frequency.

When and where to listen

7880 kHz is the all-rounder: from Germany and its neighbours it is strong at any hour, and from Britain, Scandinavia, Poland and the Alps it is clean enough for a good picture most of the day and all of the night. Transmissions follow a daily timetable, with charts every few hours and sometimes several in a row; there are gaps between them, so if the frequency is quiet, come back in a quarter of an hour.

Fax is unforgiving of fading: a dip in the signal shows as a grey band across the chart, and a strong interfering signal as a streak. A receiver within a thousand kilometres of Hamburg, with the signal steady, gives a chart on which you can actually read the pressure values.

In ShackDeck

Station catalogue → Aviation → DWD weather fax Pinneberg (7880 kHz). The program picks a public receiver that has the frequency, tunes it to 7878.1 kHz and sets the WEFAX mode; the decoder starts on the start tone and the chart appears in the picture panel, building from the top at two lines a second. No receiver, antenna or account of your own is needed. The same transmitter is also listed in the Decoders rubric as Fax DWD 7880 kHz (day and night), together with the night and daytime frequencies.