ALS162: the French time signal from Allouis on 162 kHz

What you hear

Tune to 162 kHz in CW and you get the strongest, cleanest note on the long-wave dial, and nothing else. No ticks, no dips, no gaps, no voice. Until the last day of 2016 this carrier carried France Inter, the national talk and music channel, and a listener anywhere in western Europe could follow the news from Paris on it. Since then the programme is gone and the carrier stays on, a broadcast transmitter with nothing to broadcast, because the thing it still delivers is invisible: once a second the phase of the carrier swings back and forth by about a radian, one swing for a binary zero and two for a one, and the fifty-ninth second is left without a swing to mark the minute. The bits give the minute, the hour, the day, the month, the year, the day of the week and the summer-time flags, in a family of codes close to the German DCF77. The ear cannot hear a phase shift and an ordinary waterfall cannot show one, so the signal looks like a bare carrier even though it is talking all the time.

One thing to expect: on Tuesdays from 06:00 to 10:00 UTC the transmitter is switched off for maintenance, and the frequency is simply empty.

Who transmits and why

The transmitter stands at Allouis, in the Cher department near Bourges in the centre of France, on a site that has carried long-wave broadcasting since before the Second World War, with two masts among the tallest structures in the country. The time code was added to the France Inter carrier in 1977, with the reference coming from the national time laboratory at the Paris Observatory, and over the decades a large population of equipment came to rely on it: railway station clocks, public clocks, timers in industry and utilities, and some consumer clocks sold in France. When the radio programme left long wave at the end of 2016, that equipment was reason enough to keep the transmitter going. The time service got its own name, ALS162, from Allouis and the frequency, and runs at 675 kW, a fraction of what the broadcast once used but still far more than any other time signal in Europe. The transmitter is operated by the French network company on behalf of the state.

When and where to listen

Around the clock, except the Tuesday morning break, from any receiver that covers long wave. With this much power the station is a local signal across all of France, Britain, Belgium, the Netherlands, Switzerland, western Germany and northern Spain, and still comfortable in Italy, Scandinavia and Poland. At night the sky wave reaches further, and receivers in the Baltic states or Portugal see a clean line at 162 kHz. Its neighbours on the long-wave band change from year to year as broadcasters give up their old frequencies, which makes ALS162 the fixed point of the dial.

Because the information is in the phase, there is nothing to decode by ear; the pleasure is in the history and in watching a line that strong hold its place. CW makes the carrier audible; USB with the dial set about a kilohertz low does the same with a wider filter.

In ShackDeck

Station catalogue → Time signals → ALS162 (162 kHz). The program picks a public receiver that covers 162 kHz, tunes it in CW so that the carrier becomes a note, and shows the waterfall; no receiver, antenna or account of your own is needed. The phase code is not decoded by the program.