Mode HFDL

HFDL: ACARS, squitters and positions of aircraft over oceans and remote areas, on HF.

Group	Aviation
Default frequency	8.9 MHz
Default sample rate	2 Msps
In the mode list	Data link, 8.9 MHz

Step-by-step: Tutorial-HFDL

What HFDL is

HFDL is the HF data link that gives aircraft on oceanic and polar routes a data connection to ground stations when VHF is out of range.

Frequencies and settings

Aircraft data link on HF, 3 - 22 MHz.

Setting	Value
Start frequency	8.9 MHz
Tuning range of the mode table	2 to 30 MHz
Sample rate asked	2 Msps
Lowest working rate	24 ksps
Channel width	400 kHz

OnAir takes any frequency you type; the numbers above are the mode's starting point and the range its table describes. In the app the shortcut label is Data link, 8.9 MHz.

What OnAir shows

Squitters and ground stations, ACARS, positions on a map; every channel in the band at once.

The mode's own tab has these screens: Messages, Map, Aircraft, Ground stations, Channels. The other tabs (Overview, Receiver, Scan, History) are described on the Main window page.

Tips and caveats

• Real off-air bursts decode (release 0.2.4).
• Which radio: 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.
• Try it without a radio: most modes include a built-in synthetic test signal, so you can open the screen and try the controls first.
• Receiving and the law: Receiving aircraft broadcasts is legal in many countries, but some restrict listening to or using what you hear. OnAir is a receiver. Check the rules where you live. See Legal.

Related pages

• All modes, Aviation
• Supported radios, Troubleshooting, FAQ
• More in Aviation: ADS-B, Mode S uplink, ACARS, VDL2, VDL4, Airband, VOR, ILS, NDB, Drone Remote ID, UAT, FLARM, DJI drones