How to sync your watch, step by step
- Choose your sound source. A phone’s built-in speaker is the easiest place to start: our test watch synced that way. Wired headphones or earbuds work too, and are worth trying if the speaker does not work on your device; plug them into your phone or computer (a USB-C or Lightning adapter works). Results differ between devices, so if one sound source fails, try another. 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. Most watches choose which signal to listen for from their home city: a European city for DCF77 and MSF (for example London, Paris, Berlin or Athens), a US city for WWVB (for example New York, Chicago, Denver or Los Angeles) and Tokyo for JJY. If you live elsewhere, set a matching 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. The US signal WWVB lowers its power for 0.2, 0.5 or 0.8 seconds and sends UTC, and the Japanese JJY does the reverse: it keeps the carrier on for 0.8, 0.5 or 0.2 seconds and sends Japan time.
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; 20 kHz, one third of 60 kHz, for MSF, WWVB and JJY 60; and 13.33 kHz, one third of 40 kHz, for JJY 40. 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. What matters most is placing the watch right against the speaker or earbud, because the field is strongest within the first few centimetres.
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
How do I sync a G-Shock GW-M5610 without a signal?
This is the model we tested, using a phone’s built-in speaker. Set the watch’s home city to a European city, open this page on your phone, set the volume to maximum and start the DCF77 signal. Place the watch directly on the phone’s speaker opening, then start a manual reception on the watch from timekeeping mode by holding the receive button (see the manual) until RC! appears. Keep both still. After a few minutes the display shows the reception result; the receive history then shows the time of the successful sync.
Which Casio models receive DCF77 or MSF?
All Casio models labelled Multi-Band 6 receive both, and many European Wave Ceptor models receive one or both. Popular examples: G-Shock GW-M5610 (tested), GW-5000, GW-B5600, GMW-B5000 and Rangeman GW-9400; Pro Trek PRW-3500; Lineage LCW-M100; Oceanus OCW-T200. Check the case back or manual for “Multi-Band 6”, “DCF77” or “MSF”; the exact model number matters more than the name.
Does it work with Citizen, Junghans and Seiko watches?
In principle, yes: their European radio-controlled models receive DCF77 or MSF in the same way. We have not tested them ourselves yet, so if you sync one successfully, let us know and we will add it here.
Can I sync a radio-controlled wall clock or weather station?
Yes, if it uses DCF77 or MSF. Hold the earbud against the clock’s receiver, usually in the back of the case, and start a manual search with the clock’s button (often marked “WAVE”, “RCC” or “SET”). Clocks often need longer than watches: allow up to 15 minutes.
Why does my watch report a failed reception?
Usually the signal is too weak or disturbed. Move the earbud a few millimetres, raise the volume, try another pair of wired earbuds or another device, and keep chargers and screens away. See “If it does not work” above.
Which watches work?
Any watch or clock that receives DCF77, MSF, WWVB or JJY: Casio Wave Ceptor and Multi-Band G-Shock, Citizen Radio-Controlled, Junghans Mega, Seiko Radio Sync and many wall and alarm clocks. Choose the signal your watch was made for; the manual or the case back usually lists them. The Chinese signal BPC is not available here yet, because its time code is not openly documented in enough detail.
I live in the US or Japan. Will it work?
Yes. Choose WWVB for watches sold in North America, or JJY for watches sold in Japan; the page picks a likely signal for your region automatically. The signal is created on your own device, so distance from the real transmitter plays no role. Multi-band watches work with any of the signals, as long as the home city matches, as described in step 3.
See all radio time signal stations of the world, with their frequencies, locations and ranges.
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.