OnAirWeather & science · Experimental
Decode Time signals with an SDR
OnAir receives Time signals. Time and frequency stations: DCF77 (77.5 kHz), MSF and WWVB (60 kHz), JJY (40 / 60 kHz), WWV / WWVH (2.5 - 20 MHz) and CHU (3.33 / 7.85 / 14.67 MHz): the time, date, summer time and leap second flags, the seconds tick, and how far the computer clock is off after the path delay.
What Time signals is
Time stations (DCF77, MSF, WWVB, JJY, WWV and others) broadcast the exact time, so radio clocks can set themselves.
Frequencies and where it is used
DCF77 (77.5 kHz), MSF, WWVB (60 kHz), JJY (40 / 60 kHz) carrier keying; WWV / WWVH 100 Hz BCD subcarrier and ticks; CHU 300 bit/s FSK (A frames). LF needs a radio that tunes below 1 MHz (SDRplay, Airspy HF+, RTL-SDR direct sampling).
In OnAir the tuning shortcut is LF and HF time codes; you can enter any frequency your radio reaches.
What OnAir shows for Time signals
Time, date, time zone, summer time and leap second flags, DUT1, the seconds tick and its jitter, the computer clock offset after the path delay from your position, level and SNR history.
This receiver is built from the published specification and checked end to end on simulated signals. It has had little or no testing on real transmissions yet, so reports and recordings on Discord are welcome.
Which radio you need
This is a shortwave mode, so the radio has to tune HF. An SDRplay, Airspy HF+ or an RTL-SDR in direct-sampling mode do that directly; with a HackRF an HF upconverter or a direct-sampling receiver is the usual route. A long wire or loop antenna matters more than the radio.
Questions about Time signals
Can I decode Time signals with an RTL-SDR?
An RTL-SDR can receive HF only in direct-sampling mode, which OnAir offers in its radio settings; results depend on the antenna. SDRplay and Airspy HF+ radios are better suited.
Is it legal to receive Time signals?
Receiving these signals is legal in most countries. OnAir is a receiver.
Can I try Time signals in OnAir without a radio?
Yes. Most modes include a built-in synthetic test signal, so you can open the screen and try the controls before you own a radio.
Try it without a radio
OnAir includes built-in synthetic test signals for most modes, so you can open this screen, see the layout and try the controls before you own a radio. The Tour button walks you through the app.