Tutorial Time signals

Tutorial: Time signals (WWV, DCF77, MSF, JJY and more)

What it is

Time stations broadcast the exact time on long wave and shortwave. OnAir decodes the time code, shows the date, time, summer time and leap second flags, measures the seconds tick and, with the Clock tab, compares the computer clock with the station and can set it. It is also how you get the clock exact for FT8, WSPR and the HF beacons.

What you need

• A radio that reaches the station: the long-wave ones (DCF77 77.5 kHz, MSF and WWVB 60 kHz, JJY 40 kHz) need a radio that tunes that low, for example an SDRplay (down to 1 kHz) or an Airspy HF+ (check your radio's lower limit), plus a loop or a long wire; HF stations (WWV and WWVH 2.5, 5, 10, 15 MHz) work with any radio that reaches them. The mode asks 256 ksps and works from 48 ksps.
• An HF antenna: a long wire of 10 m or more as far from household electronics as you can get it, a dipole cut for the band, or a magnetic loop for a noisy site. Keep the feed line away from switching power supplies and LED lighting, which are the usual source of S9 noise on a city balcony.
• Frequencies (database): 60 kHz (WWVB, MSF, JJY-60 share it), 77.5 kHz DCF77 (Mainflingen), 40 kHz JJY, 66.67 kHz RBU, 50 kHz RTZ, 68.5 kHz BPC, 162 kHz ALS162, 2.5, 5, 10, 15 MHz WWV/WWVH/BPM, 20 MHz WWV, 3.33, 7.85 and 14.67 MHz CHU, and RWM on 4.996, 9.996 and 14.996 MHz. The panel picks the station from the frequency (from the frequency).

Before you start

Lower the gain until the level is clear of full scale; the signals are narrow carriers. On 60 kHz three stations share the frequency; choose the one you expect in the station setting of the panel. In a city, the time code can be buried in switching noise: a loop antenna away from computers helps.

Step by step

1. Connect the radio and antenna and start OnAir. Open the group Weather & science and choose LF and HF time codes.
2. Enter the frequency of a station you can hear. The panel names the station (Station ... from the frequency).
3. Press Start. The panel says searching for the seconds, then seconds found, waiting for a whole minute, then time decoded (one minute) and time decoded, two minutes agree.
4. Open Time for the decoded date and time, Minutes for the symbols of each minute and Clock for the computer clock.
5. In Clock, choose the source (GPS or time station) and press Sync now only if you want to set the clock; see Tutorial-Time-stations-and-the-clock.

What you should see

A decoded UTC time, the station's local time with the time zone and summer time flag, DUT1, leap second announcement, the minute symbols (0 / 1 bits, M marker, - no keying, ? not read), the seconds tick position in milliseconds and its jitter, and the computer clock offset after allowing for the path delay from your position (from the ADS-B receiver position).

Reading the screen

Time: %s UTC, station time, date, day of the week, day of the year, summer time, leap second, DUT1, TAI - UTC, BPM seconds and the level and SNR. Minutes: the symbols for each minute received. Clock: Sync computer clock (source, measured offset, Sync now), and the optional NTP server for the LAN (off by default).

Options and settings

• Station and the 60 kHz preference.
• Listen and the tone/audio options.
• Act as NTP server (LAN): off by default; hobby accuracy.
• Recording of demodulated audio can be opened too (Audio, not IQ, with the tone and the recorder clock error).

Troubleshooting

• Seconds found but no time. A whole minute is needed; wait two minutes for confirmation.
• The offset jumps by 100 ms. The radio's USB buffering adds a delay; OnAir uses the earliest arrival, so the figure is typically a few ms.
• BPM or HLA do not decode. BPM sends its coded time in the pure carrier slots of every half hour; HLA (Korea) is on 5 MHz only.
• Sync refused. The signal is not locked or the offset is over 10 minutes; set the clock by hand first.
• Nothing at 77.5 kHz. Your radio does not tune that low, or the antenna is too short.

Tips

• Choose the station with the cleanest signal; the offset after path delay should agree between stations within a few ms.
• Check the clock before an FT8 or WSPR session: Tutorial-FT8.

Legal and privacy notes

Time signals are public. Setting the computer clock needs administrator rights, which the system asks for on Sync now. The NTP server option is off by default and only for your LAN. See Legal.

Under the hood

Time codes differ: DCF77 sends AM second marks and a PM code, WWVB a BCD code with phase modulation (not used), MSF two bits per second, JJY BCD in AM, WWV and WWVH BCD on a 100 Hz subcarrier plus 1000 and 1200 Hz ticks, BPM (China) UT1 and UTC alternating. OnAir reads the amplitude code of each station and cross-checks two minutes.

Related

Mode-Time-signals, Tutorial-Time-stations-and-the-clock, Tutorial-HF-beacons, Tutorial-FT8, Radio-SDRplay, Radio-Airspy, FAQ