ACARS SDR Setup and Frequency Selection

[Pavel]

Short answer: Select a local VHF ACARS channel from a current regional source, use AM demodulation with clean unsquelched audio and route it to an ACARS decoder. Frequencies and activity vary by country and airport, so do not copy a distant list without verification.

Before you start​

• Confirm that reception and message handling are lawful in your location, and avoid publishing personal or sensitive message content.
• Use the correct channel plan, modulation and decoder for AIS, classic ACARS, VDL Mode 2 or an unknown signal; they are not interchangeable audio decoders.

Step-by-step method​

1. Step 1: Choose one known active regional channel and tune a nearby airband voice signal first to verify AM reception and antenna performance.
2. Step 2: Set AM with roughly 8 to 12 kHz receive bandwidth, accurate frequency correction and moderate manual gain. Keep the signal centered during short data bursts.
3. Step 3: Route unprocessed audio to the decoder, disable enhancements and set level below clipping. Open squelch or use a threshold that never cuts the burst preamble.
4. Step 4: Run for at least an hour during active flight periods and inspect valid frames. Redact message content, aircraft identifiers and private data before sharing.

Concrete example​

A visible burst on a known ACARS frequency that produces no frames should be checked for AM mode, audio sample rate, clipping and squelch before changing antennas. A decoder cannot recover a clipped or truncated burst.

How to judge the result​

The setup is working when repeated bursts decode with valid framing and timestamps, and the same audio path remains stable across application restarts.

What to record​

• Record center frequency, sample rate, occupied bandwidth, symbol or burst timing and a short redacted I/Q sample for identification work.
• For AIS and ACARS, compare valid decoded messages over equal periods rather than raw waterfall intensity.
• A signal that stays at the same display offset when the receiver retunes may be an internal spur rather than an over-the-air transmission.

Common mistakes​

• Changing several hardware, software or RF variables at once, which removes the controlled comparison needed to identify the cause.
• Treating one autoscaled screenshot or one unusually good result as proof without recording the settings and repeating the test.
• Publishing decoded operational or personal message text can create privacy and legal issues even when reception itself is permitted.

Final check​

Replay only a lawful redacted sample with its original metadata and confirm the decoder or identification result. Remove message content and sensitive identifiers before any public upload.