Web Multiband Simulator

Link: chuanjin-su.github.io/web-multiband/

A browser-based tool to synchronize radio-controlled watches (such as Casio Multiband watches and Citizen Atomic Timekeeping watches) by simulating longwave atomic clock radio signals directly through your computer or smartphone speakers.

Supported Protocols

This simulator supports the major global time signal stations:

• BPC (China): 68.5 kHz (17.125 kHz sawtooth, 4th harmonic)
• WWVB (USA): 60 kHz (20 kHz square wave, 3rd harmonic)
• DCF77 (Germany/Europe): 77.5 kHz (15.5 kHz square, 5th harmonic)
• MSF (UK): 60 kHz (20 kHz square wave, 3rd harmonic)
• JJY (Japan): 40 kHz (13.333 kHz square wave, 3rd harmonic)

How It Works

Atomic clocks require high-frequency radio waves (e.g., 60 kHz to 77.5 kHz) to synchronize. However, standard computer sound cards cannot output audio above ~22 kHz due to the Nyquist limit.

To bypass this hardware limitation, this simulator relies on audio clipping and harmonics:

1. The Web Audio API generates a specific lower-frequency base tone (e.g., a 20 kHz square wave or 15.5 kHz sawtooth).
2. By maximizing your device's volume, the physical audio amplifier is intentionally overdriven.
3. This overdriving "clips" the waveform, turning it into a square-like wave that physically emits high-energy electromagnetic harmonics (3rd, 4th, or 5th order).
4. These electromagnetic harmonics hit the exact target frequencies (e.g., $15.5 \text{ kHz} \times 5 = 77.5 \text{ kHz}$) required by your watch's internal antenna.

How to Use

1. Verify Time Accuracy: Ensure your computer's clock is perfectly synced. You can ping a public NTP server or use an online time service.
2. Select Protocol: Choose the time signal your specific watch expects to receive.
3. Maximize Volume: Turn your computer or smartphone volume up to 100%. This is strictly required to induce the clipping distortion that generates the necessary radio harmonics.
4. Position the Watch: Place your radio-controlled watch as close to the speaker or headphones as possible.
5. Transmit: Press Start Transmitting and put your watch into its manual receive mode. Wait several minutes, as these protocols transmit only one data frame per minute.

Testing and Results

This project is tested limitedly on a MacBook Pro (2021) with a Casio G-Shock GWM5610 and a Casio Pro Trek PRW-61FC. Results may vary based on your device's hardware and environmental conditions.

Signal	GWM5610	PRW-61FC
WWVB	✅	✅
BPC	✅	✅
DCF77	✅	✅
MSF	✅	✅
JJY	✅	✅

In addition, since the author only relies on WWVB, the other protocols may not be fully tested. Feedback and contributions are very welcome to improve the simulator's accuracy and usability!

Notes

• This simulator is designed for educational and experimental purposes. Results may vary based on your device's hardware and environmental conditions.
• This tool is heavily inspired on the open-source project web-jjy.