Tutorial Datawell Buoy HF Link

Tutorial: Datawell wave-buoy HF link

What it is. Datawell Waverider buoys float at sea and measure the movement of the water. They send their data to a shore station on HF (25.5 to 35.5 MHz, up to 45 MHz on request) as simple FSK. OnAir decodes the 2FSK format (HXV: the DWR-MkIII, DWR-G and WR-SG buoys) from Datawell's published reference manual: displacements, wave height and period, water temperature, GPS position and the directional spectrum. The 4FSK format (HVA, DWR4) is not public, so only the tones and the bit stream are shown. It is a niche mode, interesting for people who live near the coast and listen on the upper HF band.

What you need

• Radio. Anything that tunes 25.5 to 35.5 MHz (up to 45 MHz on request). The mode asks for 250 ksps; the lowest rate that works is 24 ksps. An RTL-SDR, RX-888, SDRplay, HackRF or Airspy covers this range. See Supported-radios.
• Antenna. A vertical or dipole cut for around 29 to 30 MHz, outdoors. Ground-wave range of the buoys is about 50 km.
• Frequencies from the repository's frequency database and the mode's own list. The app default is 30.475 MHz. The mode lists the buoy channels sigidwiki publishes as presets; click one to tune it. The buoy's own channel is set by its owner, so others are possible. A sample recording was also checked at 29.525 MHz. The channels sit near the 10 m amateur band (28.0 to 29.7 MHz).

Before you start

• Gain: moderate. Strong signals nearby (the 10 m amateur band is next door) can overload the radio; lower the gain if the amateur signals appear in the capture.
• Keep the signal off the DC spike.
• The signal is received as USB, with the two tones about 129 Hz apart for 2FSK and about 78 Hz apart for 4FSK.

Step by step

1. Mode list, group HF utility, entry Wave buoys, HF.
2. In the Link tab choose a channel from the list of buoy channels (columns Channel, MHz, State, Format, "click to tune"), or type the frequency.
3. Press Start.
4. The format selector in the tuning bar is automatic (2FSK or 4MFSK by signal width). Choose one by hand if a buoy sends the other format than expected ("a wrong-format signal").
5. Wait for "looking for the 64-bit vector alignment (three clean vectors in a row, about 2.5 s of good signal)".

What you should see

A clear FSK signal with two tones, then the vector lock, then the heave curve and sea-state numbers.

Reading the screen

• Link. The signal spectrum (centre, tones), the symbol rate (81.92 symbols per second), the lock state and a bit-stream view (higher tone = 1).
• Waves. Heave, north and west displacements of the buoy: 12-bit sign-magnitude centimetres in 64-bit vectors at 1.28 Hz. Vectors the parity code repaired are drawn too; isolated spikes can be repairs.
• Sea state. One system word per 14 s block, 16 words (225 s) for a full set, which gives wave height and period, temperatures, GPS position and the spectrum points: PSD m2/Hz, Direction, Spread, Relative. Copy spectrum puts the spectrum on the clipboard.
• Frames. For the 4FSK format only: frames cut where the bit stream repeats, with the CRC attempts (Time UTC, CRC attempt, Frame (hex), fails). Since the coding is not public, no CRC is known to fit.
• Notes. Sources and what each part rests on, including that the parity code (BCH(63,51)) was found from a real recording and is not published.

Options and settings

Format: automatic, 2FSK or 4FSK. Clear empties the lists.

Troubleshooting

• No FSK-like signal heard yet. Check the channel, the antenna and the time of day; HF conditions change.
• Locks but spikes. Weak signal; parity repairs are shown, three or more bit errors drop or mis-repair a vector.
• 4FSK only shows bits. Expected; the coding is not public.
• Signal looks wrong. Select the format by hand.
• Interference from amateurs. The band is shared; reduce the gain or use a narrower filter.

Tips

Compare with the sample recordings on sigidwiki if you cannot hear a buoy.

Legal and privacy notes

Receive only. Datawell manuals say a transmit licence is needed in territorial waters and that 28.0 to 29.7 MHz is reserved for amateur radio; whether and how you may receive and keep this telemetry depends on your country. See Legal.

Under the hood

2FSK (HXV): 81.92 bit/s, 64-bit vectors every 0.78 s (16-bit cyclic word, heave, north and west in cm, 12 parity bits); 18 vectors make a block (sync word 0x7FFF, one system word, 16 spectrum words), 16 blocks a full set. Datawell Waverider reference manual, section 5.7. 4FSK (HVA): 163.84 bit/s.

Related

Mode-Datawell-Buoy-HF-Link, Tutorial-Weather-fax, Signal-samples, Troubleshooting