ADS-B aircraft decoding → AetherMap (FLEX-8600 + 1090 transverter, in-app via VITA-49 IQ)

Start with src/core/PanadapterStream.h and src/models/DaxIqModel.h to investigate the FlexLib/SmartSDR VITA-49 IQ stream API and determine the commandable sample rate and format. Then review src/core/WfmDemodulator.h and the listed map integration points; Phase 0 is done when the achievable rate and transverter mapping are confirmed, or the external-decoder fallback is selected.

ADS-B aircraft decoding → AetherMap (FLEX-8600 + 1090 transverter, in-app via VITA-49 IQ)

Tracking issue + implementation plan for decoding 1090 MHz ADS-B (Mode S Extended Squitter) in-app on the FlexRadio, using a 1090→IF transverter into the 8600's transverter port and the radio's wideband VITA-49 IQ stream, then plotting live aircraft on the built-in Qt map ("AetherMap"). Backed by a verified deep-research pass + a repo integration survey.

Architecture

1090 MHz antenna
   → 1090→IF transverter (down-convert to an HF/6 m IF, e.g. 1090 MHz → 28 MHz)
   → FLEX-8600 transverter port  (RX 30 kHz–54 MHz; dedicated XVTR ports)
   → radio direct-samples @ 16-bit / 245.76 Msps
   → wideband VITA-49 IF Data (time-domain IQ) stream over Gigabit Ethernet
   → AetherSDR: VITA-49 IQ ingest
   → 1090ES PPM demodulator (in-app)          ← magnitude → preamble correlate → PPM slice → 112-bit frames
   → Mode S decoder (in-app)                  ← CRC/ICAO, DF17/18 typecodes, CPR
   → ICAO-keyed aircraft roster
   → AetherMap aircraft layer

No dongle, no DAX-IQ. The demod lives in AetherSDR (same model dump1090 uses: raw IQ in → messages out).

Why this is feasible (the numbers)

The only thing the DAX-IQ 192 kHz cap ever told us is that the DAX export app is throttled — it streams ~12 Mbps when the link can do 1000. Nothing physical blocks a wider stream.

The one open empirical item (Phase 0)

What IQ sample rate will the 8600's firmware/FlexLib actually emit on a directly-commanded VITA-49 IF Data stream? We need ~2 Msps (≥~1.5 Msps workable with graceful sensitivity loss) across the ADS-B channel. This is now a software/API question, not physics — resolve it before committing Phase 2.

Verified signal & protocol facts (sources in the research report)

• Modulation: PPM at 1090 MHz, 1 Mbit/s, 8 µs four-pulse preamble (pulses at 0.0–0.5, 1.0–1.5, 3.5–4.0, 4.5–5.0 µs), then 56 or 112 µs of data. [mode-s.org, MathWorks]
• Frames: ADS-B = DF17/DF18, 112-bit. Structure: 5-bit DF + … + 24-bit parity. [mode-s.org]
• CRC: generator 0xFFF409 (24-bit; 0x1FFF409/0xFFFA0480 equivalents). The 24 parity bits are XOR-overlaid with the ICAO address, so the ICAO addr is recovered by recomputing the CRC and XORing the received parity. [EUROCONTROL, mode-s.org]
• Type codes (DF17/18): TC1–4 ident+category, TC5–8 surface position, TC9–18 airborne baro position, TC19 velocity, TC20–22 GNSS position, TC28 status, TC29 target state, TC31 op status. [pyModeS]
• CPR: even/odd pairing; global decode needs an even+odd pair in a time window; local decode needs a reference (airborne ≤180 NM, surface ≤45 NM). [pyModeS]

Decode references & licensing

• antirez/dump1090 — BSD. Best reference for the PPM demod + CRC (the algorithm we port for the in-app demodulator), no copyleft friction.
• readsb / pyModeS — GPLv3. Excellent references for CPR / typecode parsing; AetherSDR is already GPLv3 so linking is compatible, but per project precedent (HdlcCodec, Direwolf-derived AFSK demod) we implement in-tree from the BSD source + mode-s.org specs.

Codebase integration points (from survey)

Phased implementation plan

Phase 0 — pin the VITA-49 IQ rate (gates Phase 2)

• Investigate the FlexLib/SmartSDR stream create/IQ-stream API: max commandable IF Data sample rate from a native client (vs the DAX-IQ 192 kHz default), sample format (expected 32-bit float I/Q), and per-stream bandwidth on the 8600.
• Confirm transverter (XVTR) configuration: LO/offset so AetherSDR maps the IF ↔ 1090 MHz and labels the slice correctly; decide whether to use the radio's native XVTR config or app-side offset.
• Outcome: confirm ≥~1.5–2 Msps is achievable. If not, fall back to the optional external-decoder ingest (Phase 3).

Phase 1 — decode core + roster + map (no RF; build in parallel with Phase 0)

• ModeSDecoder (in-tree, from antirez BSD + mode-s.org): DF demux, CRC 0xFFF409 + ICAO recovery, DF17/18 typecode parse (ident/category, airborne+surface position, velocity), CPR global (even/odd) + local-with-reference. Unit-tested against known 112-bit message vectors (Principle XI).
• AdsbAircraftList — ICAO-hex-keyed roster (mirror AprsStationList): callsign, lat/lon, alt_baro (number or on-ground), gs, track/heading, baro/geom rate, squawk, emergency, category (A0–D7), first/last-heard; TTL eviction of stale tracks.
• ADS-B tab in the AetherModem dialog → MapView aircraft layer: markers + labels (callsign/alt/speed), click-card (full surveillance set), altitude/category color legend, optional track trails, home/QTH from radio GPS or grid.
• Nested-JSON config: transverter offset, TTL, trail length, filters, units.

Phase 2 — wideband VITA-49 IQ ingest + in-app demodulator

• Command + receive the wideband VITA-49 IF Data stream tuned to the ADS-B IF (per Phase 0).
• Mode1090Demod (from antirez BSD), on its own worker thread: magnitude |I+jQ| → preamble correlation (8 µs template) → PPM bit slicing → 112-bit frames → feed the same ModeSDecoder from Phase 1.
• UI: signal/rate stats, message-rate + CRC-pass meters; live decode → map.

Phase 3 — optional alternative source (nice-to-have)

• AdsbBeastClient — also accept Beast (port 30005) / SBS-CSV (30003) from an external dump1090/readsb. Lets users without a transverter use a cheap dongle, and is an excellent test harness for Phases 1–2 (replay real message streams into ModeSDecoder).

Out of scope (v1)

• UAT (978 MHz); MLAT; feeding aggregators; historical playback.
• ADS-B transmit (RX only).

Open questions

1. Phase 0 result — the commandable VITA-49 IQ rate on the 8600 (the one gating unknown).
2. Transverter mapping via native XVTR config vs app-side offset.
3. Map performance with hundreds of simultaneous aircraft + trails (may need marker batching beyond the PSK Reporter pattern).

Constitution touchpoints

• Principle V — nested-JSON config per feature.
• Principle XI — ModeSDecoder unit tests against known vectors; live decode → map screenshot.
• Cross-platform — VITA-49 ingest + Qt are portable; verify Linux/macOS/Windows.
• License — derive demod/decode from BSD antirez/dump1090; GPLv3 readsb/pyModeS as references.

The FLEX-8600 (245.76 Msps direct sampling, 14 MHz instantaneous bandwidth, Gigabit Ethernet, VITA-49 IQ) is a fully capable ADS-B front end via a 1090→IF transverter — no external dongle required. Plan synthesized from a verified deep-research report (5 angles, 20 sources, 25 claims adversarially verified) + a repo integration survey.