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Meteor LRPT is an external receive app for Meteor M2-series satellites that transmit LRPT (Low Rate Picture Transmission) near 137 MHz. It runs the radio in a wideband capture–style configuration, decodes the LRPT bitstream on the M4 baseband processor, and can record decoded data to the SD card. Optional MSU-MR processing (visible imaging) runs on the M0 application core and can write BMP files and a small LCD preview.

Where to find it

Receive → Meteor LRPT

Note

Pull : https://github.com/portapack-mayhem/mayhem-firmware/pull/3175 Tools : https://github.com/user-attachments/files/27760145/tools_meteor_lrpt.zip Binaries : https://github.com/user-attachments/files/27731032/hackrf_usb.zip

Antenna and frequency

• Meteor M2-3 / M2-4 LRPT is commonly received near 137.9 MHz (primary). A backup downlink near 137.1 MHz may appear on some passes; check current satellite information for your pass.
• The repository includes a Freqman preset file you can copy to the SD card: sdcard/FREQMAN/METEOR_LRPT.TXT. See Freqman manager and SD Card Content.
• these might help 👇🏻

Main controls

• Frequency: Centre frequency for LRPT (keypad or encoder; stored with app settings if enabled globally).
• RF Amp / LNA / VGA: Same idea as other receivers. If nothing decodes, avoid overdriving the front end. See Receive Quality Issues for gain behaviour.
• Volume: Audio level for the receiver UI (same pattern as other RX apps).

Troubleshooting

• No decode / flat waterfall: Check frequency for the current satellite, RHCP antenna, gain (not clipped), and M2-x / Interlv / 80k toggles vs the pass you are actually receiving.
• Recording drops / yellow REC: Reduce SPEC bandwidth, use a faster SD card, shorten cable, or record C8 instead of wider IQ where applicable (see Capture).
• Interleaved pass but garbage CADU: Confirm whether the pass is truly interleaved; confirm SOFT block size matches mode (8192 vs 16384). When in doubt, archive IQ with Capture and compare offline using repo tools under tools/meteor_lrpt/.
• MSU-MR never writes BMP: Confirm CADU file path, that CADU ASM/lock is sane, and that JPEG is baseline (not progressive). Inspect drop_bits per G4_PRODUCT.md in the repo.

Decoder options (checkboxes)

• M2-x: Select when receiving Meteor M2-x style LRPT .
• Interlv (interleaved): M2-x interleaved mode. When enabled together with a working M0 deinterleave path, the firmware uses the dual-stream deinterleave + dual Viterbi pipeline.
• Diff: NRZ-M / differential decoding option (matches the SatDump “diff” style path for the selected mode).
• Leg.corr: Legacy correlator path (for non–M2-x style receptions).
• 80k sym: Use only when you intentionally capture 80 ksymbol/s test modes. Leave off for normal 72 ksymbol/s passes.
• BMP: Saves a thin grayscale strip driven by JPEG preview heuristics on M4 — not a full MSU-MR colour product. For real images, use MSU-MR below.

Waterfall / bandwidth

The app expects a SPEC-style bandwidth suitable for LRPT (commonly 150 kHz or 250 kHz). Very wide bandwidths increase CPU and SD load; if recording glitches, reduce bandwidth or use a faster SD card (same idea as Capture yellow REC warnings).

Recording — CADU and SOFT

Two record rows may appear (similar pattern to other apps using Capture / record views):

• CADU row: Records post–Reed–Solomon 1020-byte CADU frames (logical frame length used by the decoder). Raw bytes use extension .C8 on SD (aligned with Mayhem raw S8 recording conventions).
• SOFT row: Records signed 8-bit soft symbols (I/Q pairs) for offline comparison or advanced debugging.

Critical: Do not enable CADU and SOFT recording at the same time. The baseband exposes only one capture stream at a time; enabling both can conflict.

Block sizes for SOFT files

• 16384 bytes per write: legacy / M2-x non-interleaved soft path.
• 8192 bytes per write: M2-x + Interleaved when the M0 IPC + deinterleave path is active.

SD card layout

• Recordings and products default under folder /LRPT on the SD card.
• Ensure the card is formatted and has free space before long passes. See How to Format SDCard if needed.

MSU-MR (G4) — images on SD

When MSU-MR is enabled, an M0 worker scans CADU data, extracts MSU-MR JPEG payloads where possible, decodes baseline JPEG with embedded TJpgDec, and writes 24-bit BMP files such as:

/LRPT/msumr_<apid>_<timestamp>.bmp

Operator workflow (short)

1. Record CADU with the CADU record row during the pass (recommended for a clean archive).
2. Default tail file path for the worker is /LRPT/g4_cadu.C8 — point it at your CADU capture (same .C8 convention as the CADU recorder), or adjust the Path in the app if your filename differs.
3. Enable MSU-MR and watch the status line counters (c / j / b, drops, optional ro ring overflow count when Live is on).
4. Live: Optional path where post-RS CADU is pushed from M4 into a small fixed RAM ring for near–real-time decode. If M0 cannot keep up, overflow is counted and some CADUs are dropped by design (lossless archival still prefers record to SD first).
5. Img and ^ / v: Optional paging viewer over the last decoded BMP (read-only file access).

Progressive JPEG is not supported (decoder limitation).

Related wiki pages

• Capture — IQ recording, bandwidth, REC colour warnings, .C16 / .C8 context
• C16 format — complex sample file layout when you also archive IQ
• Freqman manager — loading METEOR_LRPT.TXT
• Receive Quality Issues — gain and overload
• SD Card Content — folder layout on SD
• External apps informations — how external apps load baseband images