Tutorial Time stations and the clock

A time station broadcasts the exact time; OnAir can measure your clock against it and, when you click, correct it.

What you need

• For the LF stations (DCF77 77.5 kHz, MSF, WWVB 60 kHz, JJY 40 / 60 kHz) a radio that tunes below 1 MHz (SDRplay, Airspy HF+, RTL-SDR direct sampling). BPC (68.5 kHz) is below most radios: it needs an LF-capable radio or an up-converter.
• For the HF stations (WWV, WWVH, BPM, HLA) any radio that reaches 2.5 to 15 MHz.

Steps

1. Choose Time signals (group Weather and science) and pick a station. WWV / WWVH share 2.5, 5, 10 and 15 MHz; BPM shares them too, so choose BPM by hand. CHU was removed from this mode in 0.2.6.
2. Press Start. The Time view shows the decoded time, date, time zone, summer-time and leap-second flags, DUT1, the seconds tick and its jitter; Minutes shows each decoded minute frame.
3. The Clock view compares the received time, after the path delay from your position, with the computer clock and shows the offset. Set your position first.
4. Press Listen to hear the station.

Sync the computer clock

The Sync computer clock panel (Time signals and GNSS screens) uses GPS (read in the GNSS mode) or a time station (read in the Time signals mode) as its source.

• The radio runs one mode at a time: switch to the mode of the source and wait until it locks (for a station, until two decoded minutes agree).
• Sync now moves the computer clock by the measured offset. The system asks for the administrator password (macOS), a UAC prompt (Windows) or a polkit prompt (Linux). Nothing happens until you click, and it is never done automatically. A command you can copy is also shown.
• Accuracy: the offset includes the radio's USB and driver buffering, typically 5 to 30 ms, plus the path with a time station. It tells you whether the clock is seconds or hundreds of milliseconds off, not whether it is within 1 ms.
• An optional hobby NTP server can serve the corrected clock to other computers on your network (UDP port 123, or 1123 without administrator rights). It is off at every start, answers only private (LAN) addresses, and is for hobby use only. Do not expose it to the internet.

Related: Time signals, GNSS, FT8 and WSPR.