DDH47: DWD weather teletype from Hamburg on 147.3 kHz long wave

What you hear

Below the long wave broadcasters, where most people never tune, 147.3 kHz carries the unmistakable sound of radioteletype: a steady two-tone rattle, not the warble of a modern digital mode but the slow, even chatter of Baudot at 50 baud, with gaps between bulletins when the transmitter idles on a single tone. Decoded, it is weather in text: synoptic reports from coastal stations and ships with wind, pressure and temperature in coded groups, forecasts for the German Bight, the western and southern Baltic and the sea areas beyond, and gale warnings as they are issued. Much of it is in German, but the station names, the times and the standard code groups are readable to anyone who has seen a weather bulletin before.

Who transmits and why

The transmission comes from the Deutscher Wetterdienst, the German weather service, whose marine weather office in Hamburg has been sending weather to ships by radio for most of a century. The transmitter stands at Pinneberg, north-west of Hamburg, the DWD radio site that also carries the weather fax service. The callsign DDH47 belongs to the long wave outlet; the same bulletins go out on shortwave as DDK2 on 4583 kHz, DDH7 on 7646 kHz and DDK9 on 10100.8 kHz, so that a ship can take whichever band works for its position.

Why long wave at all: the ground wave at 147 kHz follows the curve of the sea for hundreds of kilometres without caring about the hour or the sunspot cycle, and a ship in the North Sea or the Baltic gets the same readable signal day and night. A teletype printer, or today a laptop with a sound card, is all that is needed on board, and the bulletins repeat on a fixed daily timetable.

When and where to listen

The long wave signal is strongest where it is meant to be: Germany, Denmark, the Netherlands, southern Scandinavia and Poland hear it at any hour as a solid signal that does not fade. Further away, in Britain, France or the Baltic states, it is weaker but usually still there, and at night it reaches well beyond. Public receivers that cover long wave are fewer than those on shortwave, and one on the North Sea coast is the best choice. The bulletins follow a daily timetable, so a quiet minute on the frequency usually means the transmitter is idling between them; give it a few minutes.

The catalogue tunes USB, in which the two tones come out as audio at a comfortable pitch and show as two lines on the waterfall. If you would rather read than listen, the shortwave outlet on 10100.8 kHz is the convenient one, because the program has a decoder preset for it.

In ShackDeck

Station catalogue → Aviation → DDH47 Hamburg RTTY (147.3 kHz). The program picks a public receiver that covers 147.3 kHz, tunes it and sets USB; you hear the teletype and see the pair of lines on the waterfall, with no receiver, antenna or account of your own. The program's RTTY decoder presets are on the shortwave outlets: for the text itself open the DDK9 row or the Decoders rubric entry RTTY DWD 10100.8 kHz, where the decoder is already set to 50 baud and the bulletin scrolls in the text panel.