How to sync your watch, step by step
- Choose your sound source. Wired headphones or earbuds give the best results, because the watch can lie right against them. Plug them into your computer or phone; a USB-C or Lightning adapter works. Speakers can work too, including a laptop’s or phone’s built-in speakers, but usually less reliably, so try them if you have no wired headphones. Bluetooth headphones and speakers almost never work: the wireless connection removes such high frequencies.
- Set the volume to maximum, both on the device and in any volume slider for the browser. Turn off sound effects such as “audio enhancements”, equalisers or noise suppression if your device has them.
- Check your watch’s home city. The signal carries German or UK time, and the watch converts it to its home city. Many watches only listen for DCF77 or MSF when the home city is in Europe (for example London, Paris, Berlin, Rome or Athens). If you live outside Europe, set a European home city for the sync, then switch back to your own city afterwards: the watch keeps the exact seconds and simply shifts the hours.
- Place the sound source right against the watch. The receiving antenna sits along one side of the case, often near 9 or 12 o’clock. Lay the watch on a table, face up, and put one earbud on the case next to it. With speakers, put the watch directly on or against the speaker, close to where the sound comes out. Keep the watch away from the computer, monitor and phone charger, which create interference.
- Choose the signal and press “Start signal”. Keep this page open and the screen on. You will hear a high tone with a short break every second.
- Start a manual reception on the watch. On many Casio Wave Ceptor and G-Shock models: in timekeeping mode, hold the lower-right button for about two seconds until the display shows RC!, RC or READY, or the second hand moves to a reception position. The exact button differs between models, so check your watch’s manual under “manual receive”.
- Wait without moving anything. The watch needs at least two to three complete minutes of clean signal, usually five to ten minutes in total. Most watches show their reception level during this time.
- Check the result. A successful sync is usually shown as GET, OK, Y or a signal indicator, and the reception date and time appear in the watch’s receive history. Compare the watch with the clock page; it should agree to the second.
If it does not work
- Move the earbud around the watch, a few millimetres at a time, especially along the left and top edges. Position matters more than anything else.
- Try other headphones, speakers or another device. Results vary a lot between models. Cheap wired earbuds often work better than expensive headphones, and a laptop’s headphone jack often works better than a phone. If speakers do not work, try wired headphones, and the other way round.
- Try the other signal. Many European watches receive both DCF77 and MSF.
- Keep the screen on and this tab in front. Phones and browsers pause sound in background tabs, which breaks the signal.
- Reduce interference. Unplug laptop chargers, move away from LED lamps and switch off nearby monitors for the few minutes it takes.
- Check the manual reception mode. If the watch is in an automatic night-time reception mode, it may not be listening yet. Start a manual reception after the signal is already running.
How it works
The German time signal DCF77 is broadcast by PTB, Germany’s national metrology institute, on 77.5 kHz from Mainflingen near Frankfurt. Every second, the transmitter lowers its carrier for 100 milliseconds (a 0) or 200 milliseconds (a 1). Over one minute these 59 bits spell out the date and time of the next minute; a second without a break marks the start of that minute. The UK signal MSF from Anthorn works in a similar way on 60 kHz.
A sound card cannot produce such frequencies directly. This page plays an exact fraction of them instead: 15.5 kHz, one fifth of 77.5 kHz, for DCF77, and 20 kHz, one third of 60 kHz, for MSF. Headphones, speakers and their amplifiers are never perfectly linear, so they also produce faint multiples of the tone, including the real carrier frequency. It radiates as a very weak magnetic field from the cable and coils, which a watch within a few centimetres can receive. Headphones usually work best because the watch can lie right against their coil.
The timing comes from our reference clock, which is synchronised with PTB’s atomic clocks, and the delay of your device’s audio output is subtracted. The breaks therefore start within a few hundredths of a second of the real signal, well within what a watch needs.
Questions
Which watches work?
Any watch or clock that receives DCF77 or MSF: Casio Wave Ceptor and Multi-Band G-Shock, Citizen Radio-Controlled, Junghans Mega, Seiko Radio Sync and many wall and alarm clocks. Multi-band watches, which also receive the Japanese, US or Chinese signals, work too. Watches made only for those signals (JJY, WWVB or BPC) do not react to DCF77 or MSF; the manual or the case back usually lists which signals a watch supports.
I live outside Europe. Will it work?
Yes, if your watch supports DCF77 or MSF. The signal is created here on your device, so distance plays no role. Set a European home city on the watch for the sync, as described in step 3, then switch back to your own city.
Is it legal?
The emission is extremely weak and only reaches a few centimetres, far less than many household devices. Do not try to amplify it or connect it to an antenna.
Will it harm my headphones?
No. The tone is a normal audio signal within the range headphones are built for. Just avoid listening to it.