Mode FLARM

FLARM aircraft: gliders and light aircraft on 868 MHz.

Group	Aviation
Default frequency	868.3 MHz
Default sample rate	1 Msps
In the mode list	Gliders, 868.2 / 868.4 MHz

Step-by-step: Tutorial-FLARM

What FLARM is

FLARM is the collision-avoidance broadcast of gliders and light aircraft on 868 MHz.

Frequencies and settings

Glider and light-aircraft collision-avoidance broadcasts on 868.2 and 868.4 MHz (both from one radio on 868.3 MHz, at least 1 Msps, so an RTL-SDR works), 2-FSK 100 kchip/s Manchester.

Setting	Value
Start frequency	868.3 MHz
Tuning range of the mode table	860 to 930 MHz
Sample rate asked	1 Msps
Lowest working rate	1 Msps
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 Gliders, 868.2 / 868.4 MHz.

What OnAir shows

The old protocol is decoded (device ID, aircraft type, altitude, speed, track, climb, level, distance and bearing) in a table and on the live map; the newer protocol is only counted ("FLARM (new protocol)"), without positions. Receive only, as the Open Glider Network does: positions are what the aircraft broadcast openly. The no-track and stealth flags are respected: such aircraft (and anonymous addresses) are never shown, logged, saved or exported, only counted as "privacy-flagged aircraft". Needs the receiver position (shared with ADS-B) and the computer clock set right (the packet key changes every 64 s).

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

Tips and caveats

• Checked with generated signals and impairments; recordings of real signals welcome.
• Which radio: Usually yes for narrowband signals: an RTL-SDR tunes roughly 24 MHz to 1.7 GHz at up to about 2.4 Msps. Wide signals such as TV channels need a faster radio, and OnAir says next to the source what the selected radio can do.
• 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, HFDL, Airband, VOR, ILS, NDB, Drone Remote ID, UAT, DJI drones