Tutorial HF beacons

Tutorial: HF beacons (NCDXF/IARU and others)

What it is

The NCDXF/IARU International Beacon Project runs 18 beacons around the world on five frequencies near 14, 18, 21, 24 and 28 MHz. Each one transmits for 10 seconds every 3 minutes, first a callsign in CW and then four dashes at decreasing power. By listening you learn which parts of the world you can hear, on which band, right now. OnAir turns that into a table, a map and a history. Australian Long Dashes and Russian single-letter beacons are included.

What you need

• An HF-capable receiver. An SDRplay or an Airspy HF+ tunes the HF bands directly. An RTL-SDR reaches HF only in direct-sampling mode (Radio settings, see Radio-RTL-SDR; the RTL-SDR Blog V4 uses its built-in up-converter). A HackRF or another radio that starts above the HF bands needs an up-converter such as Ham It Up or SpyVerter, which you pick in Radio settings so that the whole app shows the true frequency (see Supported-radios). The mode asks for 2 Msps and keeps working down to 250 ksps, so even a small radio is enough: the signals sit within about 3 kHz of the dial frequency. The mode asks 10 Msps and the usable bandwidth is 8 MHz. A narrow radio works too: with Step through the bands OnAir hops among the beacon frequencies.
• 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): 14.100, 18.110, 21.150, 24.930 and 28.200 MHz. All 18 beacons share each frequency in turn.
• Time: the 10 s slots are told by the computer clock, so it must be right to about a second (the panel shows computer clock, offset ...). See Tutorial-Time-stations-and-the-clock.
• Your position: set it in View > Map, because distances and bearings are computed from there (the panel notes me (placeholder: set it in View > Map)).

Before you start

Lower the gain until the ADC level in the status line is well below full scale: strong broadcast stations next to an amateur band overload a direct-sampling RTL-SDR easily, and the result is spurs that look like signals. Use Auto-tune or Optimise gain (see Your-first-reception) rather than guessing. Choose upper sideband for all dial frequencies in the lists below; the decoders listen from the dial frequency upwards. A DC spike in the middle of the spectrum is normal for some radios and is not a signal: leave a few kHz of offset if you can. The beacons are weak (the last step is 0.1 W), so a low-noise antenna matters; a signal you can barely see on the waterfall is enough.

Step by step

1. Connect the radio and antenna and start OnAir. Open the group HF utility and choose the entry whose name begins NCDXF/IARU.
2. Set your position in View > Map. Check that the computer clock is right.
3. Press Start. With a wide radio all five frequencies are watched together; with a narrow one tick Step through the bands and set s per stop.
4. Open Beacons (the table), Bands open, Map, History and Settings.
5. Click a beacon in the table: OnAir tunes to it and lets you listen (Click to select, tune and listen).

What you should see

Heard beacons with name, band, kHz, last heard UTC, the SNR now, the best SNR in the last hour and 24 hours and a trend. The 4 power steps are shown as n of 4. Bands open says per band how many beacons are heard and which is the farthest.

Reading the screen

Beacons: filter box (name, band, kHz), Beacon, kHz, Last heard UTC, SNR now, 1 h best, 24 h best, Trend, Note, Source; List order can be Heard first, Best SNR or Distance, and a type filter: All beacons, In the capture, NCDXF/IARU, Long Dashes, Single letters, Your own. Bands open: Band, In the list, Heard now, Open, Farthest. Map: a great-circle line to each beacon, coloured by SNR (red under 0 dB, amber under 10, green above). History: the last 24 hours of the selected beacon.

Options and settings

• Frequency error (ppm): the radio's error; signals are looked for at f * (1 + ppm * 1e-6).
• Clock ahead of UTC: correct a known computer clock error.
• Step through the bands, s per stop, Watch: for a capture narrower than the list.
• Your own beacons: edit the list file hf-beacons.json (Copy path, Reload, Restore the built-in list).
• Listen.

Troubleshooting

• Nothing heard. The beacons need an HF antenna and a band that is open; check 14.100 MHz in the daytime.
• Only the first call sign is heard. The weaker steps fade first; that is normal at the edge of coverage.
• Wrong beacon names. The computer clock is off by more than a second or two: the slot decides which beacon is which.
• Heard now, but far away. A real strength: that is why the beacons exist.
• Narrow radio misses most beacons. Use the stepping option or a wide radio.

Tips

• Check the Bands open table before calling CQ; it tells you in a minute where the band is open.
• The history over 24 hours shows the day/night change of a path.

Legal and privacy notes

The beacons are public propagation aids and receiving them is allowed. The map shows only the fixed beacon sites and your own entered position, which stays on your computer. See Legal.

Under the hood

Each NCDXF/IARU beacon sends its callsign in CW at 100 W, then four one-second dashes at 100 W, 10 W, 1 W and 0.1 W, in a 10 s slot; the 18 beacons cycle in a 3 minute schedule on each of the five frequencies, offset so that all five frequencies are active at once. OnAir measures the SNR of the carrier in narrow channels and uses the schedule and the clock to assign names.

Related

Mode-HF-beacons, Tutorial-Time-signals, Tutorial-WSPR, Tutorial-FT8, Radio-RTL-SDR, Live-map, FAQ