Mode Mode S uplink

Mode S uplink: interrogators, rotation periods, aircraft asked for registers, TCAS coordination.

Group	Aviation
Default frequency	1030 MHz
Default sample rate	10 Msps
In the mode list	Interrogations, 1030 MHz

Step-by-step: Tutorial-Mode-S-uplink

What Mode S uplink is

On 1030 MHz, secondary radars and collision-avoidance systems interrogate aircraft transponders. Decoding the interrogations shows which radars are around and what they ask for.

Frequencies and settings

Radar and ACAS interrogations, 1030 MHz (needs 8 Msps).

Setting	Value
Start frequency	1030 MHz
Tuning range of the mode table	1025 to 1035 MHz
Sample rate asked	10 Msps
Lowest working rate	8 Msps
Channel width	8 MHz

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 Interrogations, 1030 MHz.

What OnAir shows

Interrogator codes and rotation periods, aircraft and the registers asked for, TCAS coordination.

The mode's own tab has these screens: Interrogators, Aircraft, TCAS, Log. 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: No: this mode needs a radio that samples at 8 Msps or more, and an RTL-SDR reaches about 2.4 Msps.
• 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, ACARS, VDL2, VDL4, HFDL, Airband, VOR, ILS, NDB, Drone Remote ID, UAT, FLARM, DJI drones