DWD marine weather by RTTY on 10100.8 kHz: DDK9 at 50 baud, around the clock

What you hear

A continuous two-tone warble, the classic teletype sound: two tones 450 Hz apart switching fifty times a second, a purring "brrr" that never pauses for long. When no text is being sent the transmitter rests on a single tone, the idle mark, and on the waterfall you see one line instead of two.

Decoded, the stream is text in capital letters, bulletin after bulletin. Synoptic reports from coastal stations, lightships and ships in code groups: station number, wind, pressure, temperature, cloud. Sea-area forecasts for the North Sea and the Baltic with wind force and direction, visibility and sea state. Gale and storm warnings as they are issued. Medium-range outlooks for the coming days. Most of it is in German, as the service is first of all for German-speaking seafarers, with some bulletins in English; every bulletin begins with a header giving its type and the time of issue, so after a few minutes you learn to read the rhythm of the day.

Who transmits and why

The bulletins come from the marine weather office of Deutscher Wetterdienst in Hamburg. The callsign on 10100.8 kHz is DDK9; the same text runs on 4583 kHz as DDH7 and on 11039 kHz as DDH9, and there is a long-wave outlet on 147.3 kHz for ships without shortwave. Radioteletype is the oldest digital mode still in daily use: a ship's printer, or a laptop with a sound card, produces a clean text that can be read later, and nobody needs a subscription or a data link. For radio amateurs the station has a second role: at 50 baud and a 450 Hz shift it is the standard test signal for a new RTTY decoder, because it is on the air every hour of every day and its text makes sense.

When and where to listen

10100.8 kHz sits at the bottom edge of the 30 metre amateur band, which is why amateurs tuning across the band bump into it anyway. It behaves like 30 metres: usable day and night, best around dawn and dusk, with a reach from a few hundred to a few thousand kilometres. From anywhere in Europe the station is readable most of the time; receivers in Germany, the Netherlands and Scandinavia hear it strongest, and from southern Europe it comes through well after dark.

The parameters matter. A decoder left at the amateur setting of 45.45 baud and 170 Hz prints rubbish from this station: it must be 50 baud and 450 Hz. In USB the higher tone is the mark; if the text comes out as a string of figures and punctuation, the two tones have been taken the wrong way round.

In ShackDeck

Station catalogue → Fax and digital signals → RTTY DWD 10100.8 kHz. The program picks a public receiver that has the frequency, close to the transmitter in northern Germany, tunes it, sets the RTTY mode and passes the station's own parameters to the decoder, 50 baud and a 450 Hz shift, so there is nothing to set; no receiver, antenna or account of your own is needed. The decoder finds the pair of tones in the passband by itself and the AFC keeps it on them. The text appears in the text panel line by line, as it did on the paper of a ship's teleprinter, and stays there to be read back or cleared.