[feat](trx-rs): add AIS decoder mode and frontend

Add dual-channel AIS decode support across the SoapySDR backend, server decode pipeline, and frontend plugins, including the new AIS tab, live bar, and map filtering.

Co-authored-by: OpenAI Codex <codex@openai.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

Cargo.lock

@@ -2375,6 +2375,13 @@ dependencies = [
  "strength_reduce",
 ]
 
+[[package]]
+name = "trx-ais"
+version = "0.1.0"
+dependencies = [
+ "trx-core",
+]
+
 [[package]]
 name = "trx-app"
 version = "0.1.0"
@@ -2591,6 +2598,7 @@ dependencies = [
  "tokio-serial",
  "toml",
  "tracing",
+ "trx-ais",
  "trx-app",
  "trx-aprs",
  "trx-backend",

Cargo.toml

@@ -4,6 +4,7 @@
 
 [workspace]
 members = [
+    "src/decoders/trx-ais",
     "src/decoders/trx-aprs",
     "src/decoders/trx-cw",
     "src/decoders/trx-decode-log",

src/decoders/trx-ais/Cargo.toml

@@ -0,0 +1,11 @@
+# SPDX-FileCopyrightText: 2026 Stanislaw Grams <stanislawgrams@gmail.com>
+#
+# SPDX-License-Identifier: BSD-2-Clause
+
+[package]
+name = "trx-ais"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+trx-core = { path = "../../trx-core" }

src/decoders/trx-ais/src/lib.rs

@@ -0,0 +1,389 @@
+// SPDX-FileCopyrightText: 2026 Stanislaw Grams <stanislawgrams@gmail.com>
+//
+// SPDX-License-Identifier: BSD-2-Clause
+
+//! Basic AIS GMSK/HDLC decoder.
+//!
+//! This decoder operates on narrowband FM-demodulated audio. It uses a simple
+//! sign slicer at the symbol rate, HDLC flag detection with NRZI decoding and
+//! bit de-stuffing, then parses common AIS position/static messages.
+
+use trx_core::decode::AisMessage;
+
+const AIS_BAUD: f32 = 9_600.0;
+
+const CRC_CCITT_TABLE: [u16; 256] = {
+    let mut table = [0u16; 256];
+    let mut i = 0usize;
+    while i < 256 {
+        let mut crc = i as u16;
+        let mut j = 0;
+        while j < 8 {
+            if crc & 1 != 0 {
+                crc = (crc >> 1) ^ 0x8408;
+            } else {
+                crc >>= 1;
+            }
+            j += 1;
+        }
+        table[i] = crc;
+        i += 1;
+    }
+    table
+};
+
+fn crc16ccitt(bytes: &[u8]) -> u16 {
+    let mut crc: u16 = 0xFFFF;
+    for &b in bytes {
+        crc = (crc >> 8) ^ CRC_CCITT_TABLE[((crc ^ b as u16) & 0xFF) as usize];
+    }
+    crc ^ 0xFFFF
+}
+
+#[derive(Debug, Clone)]
+struct RawFrame {
+    payload: Vec<u8>,
+    bits: Vec<u8>,
+    crc_ok: bool,
+}
+
+#[derive(Debug, Clone)]
+pub struct AisDecoder {
+    sample_rate: f32,
+    symbol_phase: f32,
+    dc_state: f32,
+    lp_state: f32,
+    env_state: f32,
+    prev_raw_bit: u8,
+    ones: u32,
+    in_frame: bool,
+    frame_bits: Vec<u8>,
+    frames: Vec<RawFrame>,
+}
+
+impl AisDecoder {
+    pub fn new(sample_rate: u32) -> Self {
+        Self {
+            sample_rate: sample_rate.max(1) as f32,
+            symbol_phase: 0.0,
+            dc_state: 0.0,
+            lp_state: 0.0,
+            env_state: 1e-3,
+            prev_raw_bit: 0,
+            ones: 0,
+            in_frame: false,
+            frame_bits: Vec::new(),
+            frames: Vec::new(),
+        }
+    }
+
+    pub fn reset(&mut self) {
+        self.symbol_phase = 0.0;
+        self.dc_state = 0.0;
+        self.lp_state = 0.0;
+        self.env_state = 1e-3;
+        self.prev_raw_bit = 0;
+        self.ones = 0;
+        self.in_frame = false;
+        self.frame_bits.clear();
+        self.frames.clear();
+    }
+
+    pub fn process_samples(&mut self, samples: &[f32], channel: &str) -> Vec<AisMessage> {
+        for &sample in samples {
+            self.process_sample(sample);
+        }
+
+        let frames = std::mem::take(&mut self.frames);
+        let mut out = Vec::new();
+        for frame in frames {
+            if let Some(msg) = parse_frame(frame, channel) {
+                out.push(msg);
+            }
+        }
+        out
+    }
+
+    fn process_sample(&mut self, sample: f32) {
+        // Remove slow DC drift from the FM discriminator output.
+        self.dc_state += 0.0025 * (sample - self.dc_state);
+        let dc_free = sample - self.dc_state;
+
+        // Gentle low-pass smoothing to suppress narrow impulsive noise.
+        self.lp_state += 0.28 * (dc_free - self.lp_state);
+
+        // Track envelope to keep the slicer stable on weak signals.
+        self.env_state += 0.02 * (self.lp_state.abs() - self.env_state);
+        let normalized = if self.env_state > 1e-4 {
+            self.lp_state / self.env_state
+        } else {
+            self.lp_state
+        };
+
+        self.symbol_phase += AIS_BAUD;
+        while self.symbol_phase >= self.sample_rate {
+            self.symbol_phase -= self.sample_rate;
+            let raw_bit = if normalized >= 0.0 { 1 } else { 0 };
+            self.process_symbol(raw_bit);
+        }
+    }
+
+    fn process_symbol(&mut self, raw_bit: u8) {
+        let decoded_bit = if raw_bit == self.prev_raw_bit { 1 } else { 0 };
+        self.prev_raw_bit = raw_bit;
+
+        if decoded_bit == 1 {
+            self.ones += 1;
+            return;
+        }
+
+        // A zero terminates the current run of ones.
+        if self.ones >= 7 {
+            self.in_frame = false;
+            self.frame_bits.clear();
+            self.ones = 0;
+            return;
+        }
+
+        if self.ones == 6 {
+            if self.in_frame && self.frame_bits.len() >= 256 {
+                if let Some(frame) = self.bits_to_frame() {
+                    self.frames.push(frame);
+                }
+            }
+            self.frame_bits.clear();
+            self.in_frame = true;
+            self.ones = 0;
+            return;
+        }
+
+        if self.ones == 5 {
+            if self.in_frame {
+                for _ in 0..5 {
+                    self.frame_bits.push(1);
+                }
+            }
+            self.ones = 0;
+            return;
+        }
+
+        if self.in_frame {
+            for _ in 0..self.ones {
+                self.frame_bits.push(1);
+            }
+            self.frame_bits.push(0);
+        }
+        self.ones = 0;
+    }
+
+    fn bits_to_frame(&self) -> Option<RawFrame> {
+        if self.frame_bits.len() < 24 {
+            return None;
+        }
+
+        let usable_bits = self.frame_bits.len() - (self.frame_bits.len() % 8);
+        if usable_bits < 24 {
+            return None;
+        }
+
+        let bits = self.frame_bits[..usable_bits].to_vec();
+        let mut bytes = Vec::with_capacity(usable_bits / 8);
+        for chunk in bits.chunks(8) {
+            let mut byte = 0u8;
+            for (idx, &bit) in chunk.iter().enumerate() {
+                if bit != 0 {
+                    byte |= 1 << idx;
+                }
+            }
+            bytes.push(byte);
+        }
+
+        if bytes.len() < 3 {
+            return None;
+        }
+
+        let payload_len = bytes.len() - 2;
+        let payload = bytes[..payload_len].to_vec();
+        let received_fcs = u16::from_le_bytes([bytes[payload_len], bytes[payload_len + 1]]);
+        let crc_ok = crc16ccitt(&payload) == received_fcs;
+
+        Some(RawFrame {
+            payload,
+            bits,
+            crc_ok,
+        })
+    }
+}
+
+fn parse_frame(frame: RawFrame, channel: &str) -> Option<AisMessage> {
+    if !frame.crc_ok {
+        return None;
+    }
+
+    let bits = bytes_to_msb_bits(&frame.payload);
+    if bits.len() < 40 {
+        return None;
+    }
+
+    let message_type = get_uint(&bits, 0, 6)? as u8;
+    let repeat = get_uint(&bits, 6, 2)? as u8;
+    let mmsi = get_uint(&bits, 8, 30)? as u32;
+
+    let mut msg = AisMessage {
+        ts_ms: None,
+        channel: channel.to_string(),
+        message_type,
+        repeat,
+        mmsi,
+        crc_ok: frame.crc_ok,
+        bit_len: frame.bits.len(),
+        raw_bytes: frame.payload,
+        lat: None,
+        lon: None,
+        sog_knots: None,
+        cog_deg: None,
+        heading_deg: None,
+        nav_status: None,
+        vessel_name: None,
+        callsign: None,
+        destination: None,
+    };
+
+    match message_type {
+        1..=3 => {
+            msg.nav_status = get_uint(&bits, 38, 4).map(|v| v as u8);
+            msg.sog_knots = decode_tenths(get_uint(&bits, 50, 10)?, 1023);
+            msg.lon = decode_coord(get_int(&bits, 61, 28)?, 181.0);
+            msg.lat = decode_coord(get_int(&bits, 89, 27)?, 91.0);
+            msg.cog_deg = decode_tenths(get_uint(&bits, 116, 12)?, 3600);
+            msg.heading_deg = decode_heading(get_uint(&bits, 128, 9)?);
+        }
+        18 => {
+            msg.sog_knots = decode_tenths(get_uint(&bits, 46, 10)?, 1023);
+            msg.lon = decode_coord(get_int(&bits, 57, 28)?, 181.0);
+            msg.lat = decode_coord(get_int(&bits, 85, 27)?, 91.0);
+            msg.cog_deg = decode_tenths(get_uint(&bits, 112, 12)?, 3600);
+            msg.heading_deg = decode_heading(get_uint(&bits, 124, 9)?);
+        }
+        19 => {
+            msg.sog_knots = decode_tenths(get_uint(&bits, 46, 10)?, 1023);
+            msg.lon = decode_coord(get_int(&bits, 57, 28)?, 181.0);
+            msg.lat = decode_coord(get_int(&bits, 85, 27)?, 91.0);
+            msg.cog_deg = decode_tenths(get_uint(&bits, 112, 12)?, 3600);
+            msg.heading_deg = decode_heading(get_uint(&bits, 124, 9)?);
+            msg.vessel_name = decode_sixbit_text(&bits, 143, 120);
+        }
+        5 => {
+            msg.callsign = decode_sixbit_text(&bits, 70, 42);
+            msg.vessel_name = decode_sixbit_text(&bits, 112, 120);
+            msg.destination = decode_sixbit_text(&bits, 302, 120);
+        }
+        _ => {}
+    }
+
+    Some(msg)
+}
+
+fn bytes_to_msb_bits(bytes: &[u8]) -> Vec<u8> {
+    let mut bits = Vec::with_capacity(bytes.len() * 8);
+    for &byte in bytes {
+        for shift in (0..8).rev() {
+            bits.push((byte >> shift) & 1);
+        }
+    }
+    bits
+}
+
+fn get_uint(bits: &[u8], start: usize, len: usize) -> Option<u32> {
+    if len == 0 || start.checked_add(len)? > bits.len() || len > 32 {
+        return None;
+    }
+    let mut out = 0u32;
+    for &bit in &bits[start..start + len] {
+        out = (out << 1) | u32::from(bit);
+    }
+    Some(out)
+}
+
+fn get_int(bits: &[u8], start: usize, len: usize) -> Option<i32> {
+    let raw = get_uint(bits, start, len)?;
+    if len == 0 || len > 31 {
+        return None;
+    }
+    let sign_mask = 1u32 << (len - 1);
+    if raw & sign_mask == 0 {
+        Some(raw as i32)
+    } else {
+        Some((raw as i32) - ((1u32 << len) as i32))
+    }
+}
+
+fn decode_tenths(raw: u32, invalid: u32) -> Option<f32> {
+    if raw == invalid {
+        None
+    } else {
+        Some(raw as f32 / 10.0)
+    }
+}
+
+fn decode_heading(raw: u32) -> Option<u16> {
+    if raw >= 360 {
+        None
+    } else {
+        Some(raw as u16)
+    }
+}
+
+fn decode_coord(raw: i32, invalid_abs: f64) -> Option<f64> {
+    let value = raw as f64 / 600_000.0;
+    if value.abs() >= invalid_abs {
+        None
+    } else {
+        Some(value)
+    }
+}
+
+fn decode_sixbit_text(bits: &[u8], start: usize, len: usize) -> Option<String> {
+    if start.checked_add(len)? > bits.len() || len % 6 != 0 {
+        return None;
+    }
+
+    let mut out = String::new();
+    for offset in (0..len).step_by(6) {
+        let value = get_uint(bits, start + offset, 6)? as u8;
+        let ch = if value < 32 {
+            char::from(value + 64)
+        } else {
+            char::from(value)
+        };
+        if ch != '@' {
+            out.push(ch);
+        }
+    }
+
+    let trimmed = out.trim().trim_matches('@').trim().to_string();
+    if trimmed.is_empty() {
+        None
+    } else {
+        Some(trimmed)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn decodes_signed_coordinates() {
+        assert_eq!(decode_coord(60_000, 181.0), Some(0.1));
+        assert_eq!(decode_coord(-60_000, 181.0), Some(-0.1));
+    }
+
+    #[test]
+    fn decodes_sixbit_name() {
+        let bytes = [0x10_u8, 0x41_u8, 0x11_u8, 0x92_u8, 0x08_u8, 0x00_u8];
+        let bits = bytes_to_msb_bits(&bytes);
+        let text = decode_sixbit_text(&bits, 0, 36);
+        assert!(text.is_some());
+    }
+}

src/trx-client/src/audio_client.rs

@@ -18,9 +18,9 @@ use tracing::{info, warn};
 use trx_frontend::RemoteRigEntry;
 
 use trx_core::audio::{
-    read_audio_msg, write_audio_msg, AudioStreamInfo, AUDIO_MSG_APRS_DECODE, AUDIO_MSG_CW_DECODE,
-    AUDIO_MSG_FT8_DECODE, AUDIO_MSG_RX_FRAME, AUDIO_MSG_STREAM_INFO, AUDIO_MSG_TX_FRAME,
-    AUDIO_MSG_WSPR_DECODE,
+    read_audio_msg, write_audio_msg, AudioStreamInfo, AUDIO_MSG_AIS_DECODE,
+    AUDIO_MSG_APRS_DECODE, AUDIO_MSG_CW_DECODE, AUDIO_MSG_FT8_DECODE, AUDIO_MSG_RX_FRAME,
+    AUDIO_MSG_STREAM_INFO, AUDIO_MSG_TX_FRAME, AUDIO_MSG_WSPR_DECODE,
 };
 use trx_core::decode::DecodedMessage;
 
@@ -148,7 +148,8 @@ async fn handle_audio_connection(
                     let _ = rx_tx.send(Bytes::from(payload));
                 }
                 Ok((
-                    AUDIO_MSG_APRS_DECODE
+                    AUDIO_MSG_AIS_DECODE
+                    | AUDIO_MSG_APRS_DECODE
                     | AUDIO_MSG_CW_DECODE
                     | AUDIO_MSG_FT8_DECODE
                     | AUDIO_MSG_WSPR_DECODE,

src/trx-client/trx-frontend/src/lib.rs

@@ -13,7 +13,7 @@ use tokio::sync::{broadcast, mpsc, watch};
 use tokio::task::JoinHandle;
 
 use trx_core::audio::AudioStreamInfo;
-use trx_core::decode::{AprsPacket, CwEvent, DecodedMessage, Ft8Message, WsprMessage};
+use trx_core::decode::{AisMessage, AprsPacket, CwEvent, DecodedMessage, Ft8Message, WsprMessage};
 use trx_core::rig::state::{RigSnapshot, SpectrumData};
 use trx_core::{DynResult, RigRequest, RigState};
 
@@ -136,6 +136,8 @@ pub struct FrontendRuntimeContext {
     pub audio_info: Option<watch::Receiver<Option<AudioStreamInfo>>>,
     /// Decode message broadcast channel
     pub decode_rx: Option<broadcast::Sender<DecodedMessage>>,
+    /// AIS decode history (timestamp, message)
+    pub ais_history: Arc<Mutex<VecDeque<(Instant, AisMessage)>>>,
     /// APRS decode history (timestamp, packet)
     pub aprs_history: Arc<Mutex<VecDeque<(Instant, AprsPacket)>>>,
     /// CW decode history (timestamp, event)
@@ -196,6 +198,7 @@ impl FrontendRuntimeContext {
             audio_tx: None,
             audio_info: None,
             decode_rx: None,
+            ais_history: Arc::new(Mutex::new(VecDeque::new())),
             aprs_history: Arc::new(Mutex::new(VecDeque::new())),
             cw_history: Arc::new(Mutex::new(VecDeque::new())),
             ft8_history: Arc::new(Mutex::new(VecDeque::new())),

src/trx-client/trx-frontend/trx-frontend-http/assets/web/app.js

@@ -845,10 +845,11 @@ function drawSignalOverlay() {
 
   if (lastFreqHz != null && currentBandwidthHz > 0) {
     const halfBw = currentBandwidthHz / 2;
-    const xL = hzToX(lastFreqHz - halfBw);
-    const xR = hzToX(lastFreqHz + halfBw);
-    const stripW = xR - xL;
-    if (stripW > 1) {
+    for (const centerHz of visibleBandwidthCenters(lastFreqHz)) {
+      const xL = hzToX(centerHz - halfBw);
+      const xR = hzToX(centerHz + halfBw);
+      const stripW = xR - xL;
+      if (stripW <= 1) continue;
       const grd = ctx.createLinearGradient(xL, 0, xR, 0);
       grd.addColorStop(0, "rgba(240,173,78,0.05)");
       grd.addColorStop(0.2, "rgba(240,173,78,0.14)");
@@ -1204,6 +1205,31 @@ function coverageGuardBandwidthHz(mode = modeEl ? modeEl.value : "") {
   return Math.max(0, Number.isFinite(maxBw) ? maxBw : currentBandwidthHz);
 }
 
+function isAisMode(mode = modeEl ? modeEl.value : "") {
+  return String(mode || "").toUpperCase() === "AIS";
+}
+
+function coverageSpanForMode(freqHz, bandwidthHz = coverageGuardBandwidthHz(), mode = modeEl ? modeEl.value : "") {
+  if (!Number.isFinite(freqHz)) return null;
+  const safeBw = Math.max(0, Number.isFinite(bandwidthHz) ? bandwidthHz : 0);
+  let loHz = freqHz - safeBw / 2;
+  let hiHz = freqHz + safeBw / 2;
+  if (isAisMode(mode)) {
+    const aisBFreqHz = freqHz + 50_000;
+    loHz = Math.min(loHz, aisBFreqHz - safeBw / 2);
+    hiHz = Math.max(hiHz, aisBFreqHz + safeBw / 2);
+  }
+  return { loHz, hiHz };
+}
+
+function visibleBandwidthCenters(freqHz = lastFreqHz, mode = modeEl ? modeEl.value : "") {
+  if (!Number.isFinite(freqHz)) return [];
+  if (isAisMode(mode)) {
+    return [freqHz, freqHz + 50_000];
+  }
+  return [freqHz];
+}
+
 function effectiveSpectrumCoverageSpanHz(sampleRateHz) {
   const sampleRate = Number(sampleRateHz);
   if (!Number.isFinite(sampleRate) || sampleRate <= 0) return 0;
@@ -1220,17 +1246,17 @@ function requiredCenterFreqForCoverageInFrame(data, freqHz, bandwidthHz = covera
     return null;
   }
 
-  const safeBw = Math.max(0, Number.isFinite(bandwidthHz) ? bandwidthHz : 0);
   const halfSpanHz = sampleRate / 2;
-  const requiredHalfSpanHz = safeBw / 2 + spectrumCoverageMarginHz;
-  if (requiredHalfSpanHz * 2 >= sampleRate) {
+  const span = coverageSpanForMode(freqHz, bandwidthHz);
+  if (!span) return null;
+  const requiredLoHz = span.loHz - spectrumCoverageMarginHz;
+  const requiredHiHz = span.hiHz + spectrumCoverageMarginHz;
+  if (requiredHiHz - requiredLoHz >= sampleRate) {
     return alignFreqToRigStep(Math.round(freqHz));
   }
 
   const currentLoHz = currentCenterHz - halfSpanHz;
   const currentHiHz = currentCenterHz + halfSpanHz;
-  const requiredLoHz = freqHz - requiredHalfSpanHz;
-  const requiredHiHz = freqHz + requiredHalfSpanHz;
   if (requiredLoHz >= currentLoHz && requiredHiHz <= currentHiHz) {
     return null;
   }
@@ -1300,8 +1326,11 @@ function sweetSpotCandidateForFrame(data, freqHz, bandwidthHz) {
 
   const halfUsableSpanHz = usableSpanHz / 2;
   const fullHalfSpanHz = sampleRate / 2;
-  const guardHalfSpanHz = bandwidthHz / 2 + spectrumCoverageMarginHz;
-  if (guardHalfSpanHz * 2 >= usableSpanHz) {
+  const span = coverageSpanForMode(freqHz, bandwidthHz);
+  if (!span) return null;
+  const requiredLoHz = span.loHz - spectrumCoverageMarginHz;
+  const requiredHiHz = span.hiHz + spectrumCoverageMarginHz;
+  if (requiredHiHz - requiredLoHz >= usableSpanHz) {
     const fallbackCenterHz = requiredCenterFreqForCoverageInFrame(data, freqHz, bandwidthHz);
     if (!Number.isFinite(fallbackCenterHz)) return null;
     return { centerHz: fallbackCenterHz, score: Number.POSITIVE_INFINITY };
@@ -1310,8 +1339,8 @@ function sweetSpotCandidateForFrame(data, freqHz, bandwidthHz) {
   const evalHalfSpanHz = Math.max(0, (sampleRate - usableSpanHz) / 2);
   const evalMinCenterHz = currentCenterHz - evalHalfSpanHz;
   const evalMaxCenterHz = currentCenterHz + evalHalfSpanHz;
-  const fitMinCenterHz = freqHz + guardHalfSpanHz - halfUsableSpanHz;
-  const fitMaxCenterHz = freqHz - guardHalfSpanHz + halfUsableSpanHz;
+  const fitMinCenterHz = requiredHiHz - halfUsableSpanHz;
+  const fitMaxCenterHz = requiredLoHz + halfUsableSpanHz;
   const minCenterHz = Math.max(evalMinCenterHz, fitMinCenterHz);
   const maxCenterHz = Math.min(evalMaxCenterHz, fitMaxCenterHz);
   if (!Number.isFinite(minCenterHz) || !Number.isFinite(maxCenterHz) || minCenterHz > maxCenterHz) {
@@ -1334,8 +1363,8 @@ function sweetSpotCandidateForFrame(data, freqHz, bandwidthHz) {
 
   let bestStartIdx = null;
   let bestScore = Number.POSITIVE_INFINITY;
-  const signalLoHz = freqHz - bandwidthHz / 2;
-  const signalHiHz = freqHz + bandwidthHz / 2;
+  const signalLoHz = span.loHz;
+  const signalHiHz = span.hiHz;
 
   for (let startIdx = startMinIdx; startIdx <= startMaxIdx; startIdx += 1) {
     const endIdx = Math.min(maxIdx, startIdx + usableBins);
@@ -1351,7 +1380,8 @@ function sweetSpotCandidateForFrame(data, freqHz, bandwidthHz) {
     }
 
     // Keep a very small bias toward a reasonably centered passband when scores are close.
-    const centeredOffsetHz = Math.abs(candidateCenterHz - freqHz);
+    const spanMidHz = (span.loHz + span.hiHz) / 2;
+    const centeredOffsetHz = Math.abs(candidateCenterHz - spanMidHz);
     score *= 1 + centeredOffsetHz / Math.max(usableSpanHz, 1) * 0.08;
     if (score < bestScore) {
       bestScore = score;
@@ -1388,13 +1418,16 @@ function sweetSpotProbeCenters(data, freqHz, bandwidthHz) {
   if (!Number.isFinite(usableSpanHz) || usableSpanHz <= 0) return [];
 
   const halfUsableSpanHz = usableSpanHz / 2;
-  const guardHalfSpanHz = bandwidthHz / 2 + spectrumCoverageMarginHz;
-  if (guardHalfSpanHz * 2 >= usableSpanHz) {
+  const span = coverageSpanForMode(freqHz, bandwidthHz);
+  if (!span) return [];
+  const requiredLoHz = span.loHz - spectrumCoverageMarginHz;
+  const requiredHiHz = span.hiHz + spectrumCoverageMarginHz;
+  if (requiredHiHz - requiredLoHz >= usableSpanHz) {
     return [alignFreqToRigStep(Math.round(freqHz))];
   }
 
-  const minCenterHz = freqHz + guardHalfSpanHz - halfUsableSpanHz;
-  const maxCenterHz = freqHz - guardHalfSpanHz + halfUsableSpanHz;
+  const minCenterHz = requiredHiHz - halfUsableSpanHz;
+  const maxCenterHz = requiredLoHz + halfUsableSpanHz;
   if (!Number.isFinite(minCenterHz) || !Number.isFinite(maxCenterHz) || minCenterHz > maxCenterHz) {
     return [];
   }
@@ -1486,15 +1519,17 @@ function tunedFrequencyForCenterCoverage(centerHz, freqHz = lastFreqHz, bandwidt
   const sampleRate = effectiveSpectrumCoverageSpanHz(lastSpectrumData.sample_rate);
   if (!Number.isFinite(sampleRate) || sampleRate <= 0) return null;
 
-  const safeBw = Math.max(0, Number.isFinite(bandwidthHz) ? bandwidthHz : 0);
+  const span = coverageSpanForMode(freqHz, bandwidthHz);
+  if (!span) return null;
   const halfSpanHz = sampleRate / 2;
-  const requiredHalfSpanHz = safeBw / 2 + spectrumCoverageMarginHz;
-  if (requiredHalfSpanHz * 2 >= sampleRate) {
+  const requiredLoOffset = freqHz - (span.loHz - spectrumCoverageMarginHz);
+  const requiredHiOffset = (span.hiHz + spectrumCoverageMarginHz) - freqHz;
+  if (requiredLoOffset + requiredHiOffset >= sampleRate) {
     return alignFreqToRigStep(Math.round(centerHz));
   }
 
-  const minFreqHz = centerHz - halfSpanHz + requiredHalfSpanHz;
-  const maxFreqHz = centerHz + halfSpanHz - requiredHalfSpanHz;
+  const minFreqHz = centerHz - halfSpanHz + requiredLoOffset;
+  const maxFreqHz = centerHz + halfSpanHz - requiredHiOffset;
   if (freqHz >= minFreqHz && freqHz <= maxFreqHz) {
     return null;
   }
@@ -1953,10 +1988,15 @@ function render(update) {
     }
   }
   const modeUpper = update.status && update.status.mode ? normalizeMode(update.status.mode).toUpperCase() : "";
+  const aisStatus = document.getElementById("ais-status");
   const aprsStatus = document.getElementById("aprs-status");
   const cwStatus = document.getElementById("cw-status");
   const ft8Status = document.getElementById("ft8-status");
   const wsprStatus = document.getElementById("wspr-status");
+  if (aisStatus && modeUpper !== "AIS" && aisStatus.textContent === "Receiving") {
+    aisStatus.textContent = "Connected, listening for packets";
+  }
+  if (window.updateAisBar) window.updateAisBar();
   if (aprsStatus && modeUpper !== "PKT" && aprsStatus.textContent === "Receiving") {
     aprsStatus.textContent = "Connected, listening for packets";
   }
@@ -2644,6 +2684,7 @@ const MODE_BW_DEFAULTS = {
   USB:    [2_700,  300,   6_000,  100],
   AM:     [9_000,  500,   20_000, 500],
   FM:     [12_500, 2_500, 25_000, 500],
+  AIS:    [25_000, 12_500, 50_000, 500],
   WFM:    [180_000, 50_000,300_000,5_000],
   DIG:    [3_000,  300,   6_000,  100],
   PKT:    [25_000, 300,  50_000,  500],
@@ -2925,8 +2966,9 @@ let aprsRadioPath = null;
 const stationMarkers = new Map();
 const locatorMarkers = new Map();
 const mapMarkers = new Set();
-const mapFilter = { aprs: true, ft8: true, wspr: true };
+const mapFilter = { ais: true, aprs: true, ft8: true, wspr: true };
 const APRS_TRACK_MAX_POINTS = 64;
+const aisMarkers = new Map();
 
 window.clearMapMarkersByType = function(type) {
   if (type === "aprs") {
@@ -2944,6 +2986,17 @@ window.clearMapMarkersByType = function(type) {
     return;
   }
 
+  if (type === "ais") {
+    aisMarkers.forEach((entry) => {
+      if (entry && entry.marker) {
+        if (aprsMap && aprsMap.hasLayer(entry.marker)) entry.marker.removeFrom(aprsMap);
+        mapMarkers.delete(entry.marker);
+      }
+    });
+    aisMarkers.clear();
+    return;
+  }
+
   if (type === "ft8" || type === "wspr") {
     const prefix = `${type}:`;
     for (const [key, entry] of locatorMarkers.entries()) {
@@ -3041,9 +3094,16 @@ function initAprsMap() {
   }
   applyMapFilter();
 
+  const aisFilter = document.getElementById("map-filter-ais");
   const aprsFilter = document.getElementById("map-filter-aprs");
   const ft8Filter = document.getElementById("map-filter-ft8");
   const wsprFilter = document.getElementById("map-filter-wspr");
+  if (aisFilter) {
+    aisFilter.addEventListener("change", () => {
+      mapFilter.ais = aisFilter.checked;
+      applyMapFilter();
+    });
+  }
   if (aprsFilter) {
     aprsFilter.addEventListener("change", () => {
       mapFilter.aprs = aprsFilter.checked;
@@ -3188,6 +3248,30 @@ function buildAprsPopupHtml(call, lat, lon, info, pkt) {
     `</div>`;
 }
 
+function buildAisPopupHtml(msg) {
+  const age = msg?._tsMs ? formatTimeAgo(msg._tsMs) : null;
+  const distKm = (serverLat != null && serverLon != null && msg?.lat != null && msg?.lon != null)
+    ? haversineKm(serverLat, serverLon, msg.lat, msg.lon)
+    : null;
+  const distStr = distKm != null
+    ? (distKm < 1 ? `${Math.round(distKm * 1000)} m` : `${distKm.toFixed(1)} km`)
+    : null;
+  const meta = [age, distStr, msg?.channel ? `AIS ${escapeMapHtml(msg.channel)}` : null].filter(Boolean).join(" &middot; ");
+  let rows = "";
+  rows += `<tr><td class="aprs-popup-label">MMSI</td><td>${escapeMapHtml(String(msg.mmsi || "--"))}</td></tr>`;
+  rows += `<tr><td class="aprs-popup-label">Type</td><td>${escapeMapHtml(String(msg.message_type || "--"))}</td></tr>`;
+  if (msg?.sog_knots != null) rows += `<tr><td class="aprs-popup-label">SOG</td><td>${Number(msg.sog_knots).toFixed(1)} kn</td></tr>`;
+  if (msg?.cog_deg != null) rows += `<tr><td class="aprs-popup-label">COG</td><td>${Number(msg.cog_deg).toFixed(1)}&deg;</td></tr>`;
+  if (msg?.lat != null && msg?.lon != null) rows += `<tr><td class="aprs-popup-label">Pos</td><td>${msg.lat.toFixed(5)}, ${msg.lon.toFixed(5)}</td></tr>`;
+  const info = [msg?.vessel_name, msg?.callsign, msg?.destination].filter(Boolean).map(escapeMapHtml).join(" · ");
+  return `<div class="aprs-popup">` +
+    `<div class="aprs-popup-call">${escapeMapHtml(msg?.vessel_name || `MMSI ${msg?.mmsi || "--"}`)}</div>` +
+    (meta ? `<div class="aprs-popup-meta">${meta}</div>` : "") +
+    (rows ? `<table class="aprs-popup-table">${rows}</table>` : "") +
+    (info ? `<div class="aprs-popup-info">${info}</div>` : "") +
+    `</div>`;
+}
+
 function aprsPositionsEqual(a, b) {
   if (!a || !b) return false;
   return Math.abs(a[0] - b[0]) < 0.000001 && Math.abs(a[1] - b[1]) < 0.000001;
@@ -3276,6 +3360,31 @@ window.aprsMapAddStation = function(call, lat, lon, info, symbolTable, symbolCod
   }
 };
 
+window.aisMapAddVessel = function(msg) {
+  if (msg == null || msg.lat == null || msg.lon == null || !Number.isFinite(msg.mmsi)) return;
+  if (!aprsMap) initAprsMap();
+  const key = String(msg.mmsi);
+  const popupHtml = buildAisPopupHtml(msg);
+  const existing = aisMarkers.get(key);
+  if (existing && existing.marker) {
+    existing.msg = msg;
+    existing.marker.setLatLng([msg.lat, msg.lon]);
+    existing.marker.setPopupContent(popupHtml);
+    return;
+  }
+  if (!aprsMap) return;
+  const marker = L.circleMarker([msg.lat, msg.lon], {
+    radius: 6,
+    color: "#e2553d",
+    fillColor: "#ff7559",
+    fillOpacity: 0.82,
+  }).addTo(aprsMap).bindPopup(popupHtml);
+  marker.__trxType = "ais";
+  mapMarkers.add(marker);
+  aisMarkers.set(key, { marker, msg });
+  applyMapFilter();
+};
+
 function maidenheadToBounds(grid) {
   if (!grid || grid.length < 4) return null;
   const g = grid.toUpperCase();
@@ -3310,6 +3419,7 @@ function applyMapFilter() {
   mapMarkers.forEach((marker) => {
     const type = marker.__trxType;
     const visible =
+      (type === "ais" && mapFilter.ais) ||
       (type === "aprs" && mapFilter.aprs) ||
       (type === "ft8" && mapFilter.ft8) ||
       (type === "wspr" && mapFilter.wspr);
@@ -3999,15 +4109,18 @@ document.getElementById("copyright-year").textContent = new Date().getFullYear()
 let decodeSource = null;
 let decodeConnected = false;
 function updateDecodeStatus(text) {
+  const ais = document.getElementById("ais-status");
   const aprs = document.getElementById("aprs-status");
   const cw = document.getElementById("cw-status");
   const ft8 = document.getElementById("ft8-status");
+  if (ais && ais.textContent !== "Receiving") ais.textContent = text;
   if (aprs && aprs.textContent !== "Receiving") aprs.textContent = text;
   if (cw && cw.textContent !== "Receiving") cw.textContent = text;
   if (ft8 && ft8.textContent !== "Receiving") ft8.textContent = text;
 }
 function connectDecode() {
   if (decodeSource) { decodeSource.close(); }
+  if (window.resetAisHistoryView) window.resetAisHistoryView();
   if (window.resetAprsHistoryView) window.resetAprsHistoryView();
   if (window.resetCwHistoryView) window.resetCwHistoryView();
   if (window.resetFt8HistoryView) window.resetFt8HistoryView();
@@ -4020,6 +4133,7 @@ function connectDecode() {
   decodeSource.onmessage = (evt) => {
     try {
       const msg = JSON.parse(evt.data);
+      if (msg.type === "ais" && window.onServerAis) window.onServerAis(msg);
       if (msg.type === "aprs" && window.onServerAprs) window.onServerAprs(msg);
       if (msg.type === "cw" && window.onServerCw) window.onServerCw(msg);
       if (msg.type === "ft8" && window.onServerFt8) window.onServerFt8(msg);
@@ -4796,36 +4910,38 @@ function drawSpectrum(data) {
   // ── BW strip (drawn before spectrum so traces appear on top) ──────────────
   if (lastFreqHz != null && currentBandwidthHz > 0) {
     if (_bwDragEdge) {
-      const xMid = hzToX(lastFreqHz);
-      // Bottom bookmark tab centered on the dial frequency, shown only while resizing BW
+      // Bottom bookmark tab centered on each visible channel, shown while resizing BW
       const bwText = formatBwLabel(currentBandwidthHz);
-      ctx.save();
-      ctx.font = `bold ${Math.round(10 * dpr)}px sans-serif`;
-      const tw = ctx.measureText(bwText).width;
-      const PAD  = 6 * dpr;
-      const TAB_H = 16 * dpr;
-      const TAB_OFFSET = 4 * dpr;
-      const tabX = Math.max(0, Math.min(W - tw - PAD * 2, xMid - (tw + PAD * 2) / 2));
-      const tabBottom = H - TAB_OFFSET;
-      const tabY = tabBottom - TAB_H;
-      const r = 3 * dpr;
-      // Rounded-bottom tab shape (flat top)
-      ctx.fillStyle = "rgba(240,173,78,0.85)";
-      ctx.beginPath();
-      ctx.moveTo(tabX, tabY);
-      ctx.lineTo(tabX + tw + PAD * 2, tabY);
-      ctx.lineTo(tabX + tw + PAD * 2, tabBottom - r);
-      ctx.arcTo(tabX + tw + PAD * 2, tabBottom, tabX + tw + PAD * 2 - r, tabBottom, r);
-      ctx.lineTo(tabX + r, tabBottom);
-      ctx.arcTo(tabX, tabBottom, tabX, tabBottom - r, r);
-      ctx.lineTo(tabX, tabY);
-      ctx.closePath();
-      ctx.fill();
-      // Tab text
-      ctx.fillStyle = spectrumBgColor();
-      ctx.textAlign = "left";
-      ctx.fillText(bwText, tabX + PAD, tabBottom - 4 * dpr);
-      ctx.restore();
+      for (const centerHz of visibleBandwidthCenters(lastFreqHz)) {
+        const xMid = hzToX(centerHz);
+        ctx.save();
+        ctx.font = `bold ${Math.round(10 * dpr)}px sans-serif`;
+        const tw = ctx.measureText(bwText).width;
+        const PAD  = 6 * dpr;
+        const TAB_H = 16 * dpr;
+        const TAB_OFFSET = 4 * dpr;
+        const tabX = Math.max(0, Math.min(W - tw - PAD * 2, xMid - (tw + PAD * 2) / 2));
+        const tabBottom = H - TAB_OFFSET;
+        const tabY = tabBottom - TAB_H;
+        const r = 3 * dpr;
+        // Rounded-bottom tab shape (flat top)
+        ctx.fillStyle = "rgba(240,173,78,0.85)";
+        ctx.beginPath();
+        ctx.moveTo(tabX, tabY);
+        ctx.lineTo(tabX + tw + PAD * 2, tabY);
+        ctx.lineTo(tabX + tw + PAD * 2, tabBottom - r);
+        ctx.arcTo(tabX + tw + PAD * 2, tabBottom, tabX + tw + PAD * 2 - r, tabBottom, r);
+        ctx.lineTo(tabX + r, tabBottom);
+        ctx.arcTo(tabX, tabBottom, tabX, tabBottom - r, r);
+        ctx.lineTo(tabX, tabY);
+        ctx.closePath();
+        ctx.fill();
+        // Tab text
+        ctx.fillStyle = spectrumBgColor();
+        ctx.textAlign = "left";
+        ctx.fillText(bwText, tabX + PAD, tabBottom - 4 * dpr);
+        ctx.restore();
+      }
     }
   }
 
@@ -5188,11 +5304,24 @@ if (overviewCanvas) {
 function getBwEdgeHit(cssX, cssW, range) {
   if (!lastFreqHz || !currentBandwidthHz || !lastSpectrumData) return null;
   const halfBw = currentBandwidthHz / 2;
-  const xL = ((lastFreqHz - halfBw - range.visLoHz) / range.visSpanHz) * cssW;
-  const xR = ((lastFreqHz + halfBw - range.visLoHz) / range.visSpanHz) * cssW;
   const HIT = 8;
-  if (Math.abs(cssX - xL) < HIT) return "left";
-  if (Math.abs(cssX - xR) < HIT) return "right";
+  let bestEdge = null;
+  let bestDist = Number.POSITIVE_INFINITY;
+  for (const centerHz of visibleBandwidthCenters(lastFreqHz)) {
+    const xL = ((centerHz - halfBw - range.visLoHz) / range.visSpanHz) * cssW;
+    const xR = ((centerHz + halfBw - range.visLoHz) / range.visSpanHz) * cssW;
+    const distL = Math.abs(cssX - xL);
+    const distR = Math.abs(cssX - xR);
+    if (distL < HIT && distL < bestDist) {
+      bestEdge = "left";
+      bestDist = distL;
+    }
+    if (distR < HIT && distR < bestDist) {
+      bestEdge = "right";
+      bestDist = distR;
+    }
+  }
+  if (bestEdge) return bestEdge;
   return null;
 }
 

src/trx-client/trx-frontend/trx-frontend-http/assets/web/index.html

@@ -78,6 +78,7 @@
       <div class="overview-strip">
         <canvas id="overview-canvas" aria-hidden="true"></canvas>
         <div id="rds-ps-overlay" aria-live="polite" aria-label="RDS station name"></div>
+        <div id="ais-bar-overlay" aria-live="polite" aria-label="Recent AIS messages"></div>
         <div id="aprs-bar-overlay" aria-live="polite" aria-label="Recent APRS frames"></div>
       </div>
       <div id="spectrum-bookmark-axis"></div>
@@ -348,6 +349,7 @@
     <div id="tab-plugins" class="tab-panel" style="display:none;">
       <div class="sub-tab-bar">
         <button class="sub-tab active" data-subtab="overview">Overview</button>
+        <button class="sub-tab" data-subtab="ais">AIS</button>
         <button class="sub-tab" data-subtab="aprs">APRS</button>
         <button class="sub-tab" data-subtab="cw">CW</button>
         <button class="sub-tab" data-subtab="ft8">FT8</button>
@@ -355,6 +357,12 @@
         <button class="sub-tab" data-subtab="rds">RDS</button>
       </div>
       <div id="subtab-overview" class="sub-tab-panel">
+        <div class="plugin-item">
+          <strong>AIS Decoder</strong>
+          <div style="color:var(--text-muted); font-size:0.85rem; margin-top:0.2rem;">
+            Decodes dual-channel AIS traffic from RX audio using 9.6 kbit/s GMSK and HDLC.
+          </div>
+        </div>
         <div class="plugin-item">
           <strong>APRS Decoder</strong>
           <div style="color:var(--text-muted); font-size:0.85rem; margin-top:0.2rem;">
@@ -411,6 +419,14 @@
         </div>
         <pre id="rds-raw" class="rds-raw">--</pre>
       </div>
+      <div id="subtab-ais" class="sub-tab-panel" style="display:none;">
+        <div class="aprs-controls">
+          <button id="ais-clear-btn" type="button">Clear</button>
+          <input id="ais-filter" class="ft8-filter" type="text" placeholder="Filter (e.g. MMSI, vessel, A)" />
+          <small id="ais-status" style="color:var(--text-muted);">Waiting for server decode</small>
+        </div>
+        <div id="ais-messages"></div>
+      </div>
       <div id="subtab-aprs" class="sub-tab-panel" style="display:none;">
         <div class="aprs-controls">
           <button id="aprs-clear-btn" type="button">Clear</button>
@@ -469,6 +485,7 @@
     </div>
     <div id="tab-map" class="tab-panel" style="display:none;">
       <div class="map-controls">
+        <label><input type="checkbox" id="map-filter-ais" checked /> AIS</label>
         <label><input type="checkbox" id="map-filter-aprs" checked /> APRS</label>
         <label><input type="checkbox" id="map-filter-ft8" checked /> FT8</label>
         <label><input type="checkbox" id="map-filter-wspr" checked /> WSPR</label>
@@ -504,6 +521,7 @@
     </div>
   </div>
   <script src="/app.js"></script>
+  <script src="/ais.js"></script>
   <script src="/aprs.js"></script>
   <script src="/ft8.js"></script>
   <script src="/wspr.js"></script>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/ais.js

@@ -0,0 +1,165 @@
+// --- AIS Decoder Plugin (server-side decode) ---
+const aisStatus = document.getElementById("ais-status");
+const aisMessagesEl = document.getElementById("ais-messages");
+const aisFilterInput = document.getElementById("ais-filter");
+const aisClearBtn = document.getElementById("ais-clear-btn");
+const aisBarOverlay = document.getElementById("ais-bar-overlay");
+const AIS_MAX_MESSAGES = 200;
+const AIS_BAR_WINDOW_MS = 15 * 60 * 1000;
+let aisFilterText = "";
+let aisMessageHistory = [];
+
+function aisDisplayName(msg) {
+  return msg.vessel_name || msg.callsign || `MMSI ${msg.mmsi}`;
+}
+
+function renderAisRow(msg) {
+  const row = document.createElement("div");
+  row.className = "ais-message";
+  const ts = msg._ts || new Date().toLocaleTimeString([], { hour: "2-digit", minute: "2-digit", second: "2-digit" });
+  const name = aisDisplayName(msg);
+  const channel = msg.channel ? `AIS-${msg.channel}` : "AIS";
+  const pos = msg.lat != null && msg.lon != null
+    ? ` <a class="aprs-pos" href="javascript:void(0)" onclick="window.navigateToAprsMap(${msg.lat},${msg.lon})">${msg.lat.toFixed(4)}, ${msg.lon.toFixed(4)}</a>`
+    : "";
+  const motion = [
+    msg.sog_knots != null ? `${Number(msg.sog_knots).toFixed(1)} kn` : null,
+    msg.cog_deg != null ? `${Number(msg.cog_deg).toFixed(1)}°` : null,
+  ].filter(Boolean).join(" · ");
+  row.dataset.filterText = [
+    name,
+    msg.mmsi,
+    msg.channel,
+    msg.vessel_name,
+    msg.callsign,
+    msg.destination,
+  ]
+    .filter(Boolean)
+    .join(" ")
+    .toUpperCase();
+  row.innerHTML =
+    `<span class="ais-time">${ts}</span>` +
+    `<span class="ais-call">${escapeMapHtml(name)}</span> ` +
+    `<span class="aprs-time">[${escapeMapHtml(channel)}]</span> ` +
+    `<span>MMSI ${escapeMapHtml(String(msg.mmsi))}</span>` +
+    (motion ? ` <span>${escapeMapHtml(motion)}</span>` : "") +
+    pos;
+  applyAisFilterToRow(row);
+  return row;
+}
+
+function applyAisFilterToRow(row) {
+  if (!aisFilterText) {
+    row.style.display = "";
+    return;
+  }
+  const message = row.dataset.filterText || "";
+  row.style.display = message.includes(aisFilterText) ? "" : "none";
+}
+
+function applyAisFilterToAll() {
+  if (!aisMessagesEl) return;
+  const rows = aisMessagesEl.querySelectorAll(".ais-message");
+  rows.forEach((row) => applyAisFilterToRow(row));
+}
+
+function updateAisBar() {
+  if (!aisBarOverlay) return;
+  const isAis = (document.getElementById("mode")?.value || "").toUpperCase() === "AIS";
+  const cutoffMs = Date.now() - AIS_BAR_WINDOW_MS;
+  const messages = aisMessageHistory.filter((msg) => msg._tsMs >= cutoffMs);
+  if (!isAis || messages.length === 0) {
+    aisBarOverlay.style.display = "none";
+    aisBarOverlay.innerHTML = "";
+    return;
+  }
+
+  let html = '<div class="aprs-bar-header"><span class="aprs-bar-title"><span class="aprs-bar-title-word">AIS</span><span class="aprs-bar-title-word">Live</span></span><span class="aprs-bar-clear-wrap"><span class="aprs-bar-clear" role="button" tabindex="0" onclick="window.clearAisBar()" onkeydown="if(event.key===\'Enter\'||event.key===\' \'){event.preventDefault();window.clearAisBar();}" aria-label="Clear AIS overlay">Clear</span></span><span class="aprs-bar-window">Last 15 minutes</span></div>';
+  for (const msg of messages) {
+    const ts = msg._ts ? `<span class="aprs-bar-time">${msg._ts}</span>` : "";
+    const pin = msg.lat != null && msg.lon != null
+      ? `<button class="aprs-bar-pin" title="${msg.lat.toFixed(4)}, ${msg.lon.toFixed(4)}" onclick="window.navigateToAprsMap(${msg.lat},${msg.lon})">📍</button>`
+      : "";
+    const name = `<span class="ais-call">${escapeMapHtml(aisDisplayName(msg))}</span>`;
+    const channel = msg.channel ? ` AIS-${escapeMapHtml(msg.channel)}` : "";
+    const details = [
+      `MMSI ${escapeMapHtml(String(msg.mmsi))}`,
+      msg.sog_knots != null ? `${Number(msg.sog_knots).toFixed(1)} kn` : null,
+      msg.cog_deg != null ? `${Number(msg.cog_deg).toFixed(1)}°` : null,
+    ].filter(Boolean).join(" · ");
+    html += `<div class="aprs-bar-frame">` +
+      `<div class="aprs-bar-frame-main">${ts}${pin}${name}${channel}: ${details}</div>` +
+      `</div>`;
+  }
+  aisBarOverlay.innerHTML = html;
+  aisBarOverlay.style.display = "flex";
+}
+window.updateAisBar = updateAisBar;
+window.clearAisBar = function() {
+  window.resetAisHistoryView();
+};
+
+window.resetAisHistoryView = function() {
+  if (aisMessagesEl) aisMessagesEl.innerHTML = "";
+  aisMessageHistory = [];
+  updateAisBar();
+  if (window.clearMapMarkersByType) window.clearMapMarkersByType("ais");
+};
+
+function addAisMessage(msg) {
+  const tsMs = Number.isFinite(msg.ts_ms) ? Number(msg.ts_ms) : Date.now();
+  msg._tsMs = tsMs;
+  msg._ts = new Date(tsMs).toLocaleTimeString([], { hour: "2-digit", minute: "2-digit", second: "2-digit" });
+
+  aisMessageHistory.unshift(msg);
+  if (aisMessageHistory.length > AIS_MAX_MESSAGES) aisMessageHistory.length = AIS_MAX_MESSAGES;
+  updateAisBar();
+
+  if (aisMessagesEl) {
+    const row = renderAisRow(msg);
+    aisMessagesEl.prepend(row);
+    while (aisMessagesEl.children.length > AIS_MAX_MESSAGES) {
+      aisMessagesEl.removeChild(aisMessagesEl.lastChild);
+    }
+  }
+
+  if (msg.lat != null && msg.lon != null && window.aisMapAddVessel) {
+    window.aisMapAddVessel(msg);
+  }
+}
+
+if (aisClearBtn) {
+  aisClearBtn.addEventListener("click", async () => {
+    try {
+      await postPath("/clear_ais_decode");
+      window.resetAisHistoryView();
+    } catch (e) {
+      console.error("AIS clear failed", e);
+    }
+  });
+}
+
+if (aisFilterInput) {
+  aisFilterInput.addEventListener("input", () => {
+    aisFilterText = aisFilterInput.value.trim().toUpperCase();
+    applyAisFilterToAll();
+  });
+}
+
+window.onServerAis = function(msg) {
+  if (aisStatus) aisStatus.textContent = "Receiving";
+  addAisMessage({
+    channel: msg.channel,
+    message_type: msg.message_type,
+    mmsi: msg.mmsi,
+    lat: msg.lat,
+    lon: msg.lon,
+    sog_knots: msg.sog_knots,
+    cog_deg: msg.cog_deg,
+    heading_deg: msg.heading_deg,
+    vessel_name: msg.vessel_name,
+    callsign: msg.callsign,
+    destination: msg.destination,
+    ts_ms: msg.ts_ms,
+  });
+};

src/trx-client/trx-frontend/trx-frontend-http/assets/web/style.css

@@ -629,7 +629,8 @@ small { color: var(--text-muted); }
   color: var(--text-muted);
   background: color-mix(in srgb, var(--card-bg) 62%, transparent);
 }
-#aprs-bar-overlay {
+#aprs-bar-overlay,
+#ais-bar-overlay {
   display: none;
   position: absolute;
   top: 50%;
@@ -1087,11 +1088,16 @@ small { color: var(--text-muted); }
 .sub-tab:hover:not(.active) { color: var(--text); }
 #aprs-map { min-height: 150px; border-radius: 6px; }
 .aprs-controls { display: flex; gap: 0.6rem; align-items: center; margin-bottom: 0.75rem; }
-#aprs-packets { max-height: 360px; overflow-y: auto; border: 1px solid var(--border-light); border-radius: 6px; background: var(--input-bg); font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace; }
+#aprs-packets,
+#ais-messages { max-height: 360px; overflow-y: auto; border: 1px solid var(--border-light); border-radius: 6px; background: var(--input-bg); font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace; }
 .aprs-packet { font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace; font-size: 0.82rem; padding: 0.35rem 0.5rem; border-bottom: 1px solid var(--border); line-height: 1.4; }
 .aprs-packet:last-child { border-bottom: none; }
+.ais-message { font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace; font-size: 0.82rem; padding: 0.35rem 0.5rem; border-bottom: 1px solid var(--border); line-height: 1.4; }
+.ais-message:last-child { border-bottom: none; }
 .aprs-call { color: var(--accent-green); font-weight: 600; }
+.ais-call { color: var(--accent-red); font-weight: 600; }
 .aprs-time { color: var(--text-muted); margin-right: 0.5rem; }
+.ais-time { color: var(--text-muted); margin-right: 0.5rem; }
 .aprs-symbol { display: inline-block; width: 24px; height: 24px; background-size: 384px 192px; vertical-align: middle; margin-right: 0.3rem; }
 .aprs-pos { color: var(--accent-green); text-decoration: none; margin-left: 0.3rem; font-size: 0.8rem; }
 .aprs-pos:hover { text-decoration: underline; }

src/trx-client/trx-frontend/trx-frontend-http/src/api.rs

@@ -258,6 +258,11 @@ pub async fn decode_events(
 
     let history = {
         let mut out = Vec::new();
+        out.extend(
+            crate::server::audio::snapshot_ais_history(context.get_ref())
+                .into_iter()
+                .map(trx_core::decode::DecodedMessage::Ais),
+        );
         out.extend(
             crate::server::audio::snapshot_aprs_history(context.get_ref())
                 .into_iter()
@@ -685,6 +690,14 @@ pub async fn clear_aprs_decode(
     send_command(&rig_tx, RigCommand::ResetAprsDecoder).await
 }
 
+#[post("/clear_ais_decode")]
+pub async fn clear_ais_decode(
+    context: web::Data<Arc<FrontendRuntimeContext>>,
+) -> Result<HttpResponse, Error> {
+    crate::server::audio::clear_ais_history(context.get_ref());
+    Ok(HttpResponse::Ok().finish())
+}
+
 #[post("/clear_cw_decode")]
 pub async fn clear_cw_decode(
     context: web::Data<Arc<FrontendRuntimeContext>>,
@@ -938,6 +951,7 @@ pub fn configure(cfg: &mut web::ServiceConfig) {
         .service(set_cw_tone)
         .service(toggle_ft8_decode)
         .service(toggle_wspr_decode)
+        .service(clear_ais_decode)
         .service(clear_aprs_decode)
         .service(clear_cw_decode)
         .service(clear_ft8_decode)
@@ -954,6 +968,7 @@ pub fn configure(cfg: &mut web::ServiceConfig) {
         .service(logo)
         .service(style_css)
         .service(app_js)
+        .service(ais_js)
         .service(aprs_js)
         .service(ft8_js)
         .service(wspr_js)
@@ -1020,6 +1035,16 @@ async fn aprs_js() -> impl Responder {
         .body(status::APRS_JS)
 }
 
+#[get("/ais.js")]
+async fn ais_js() -> impl Responder {
+    HttpResponse::Ok()
+        .insert_header((
+            header::CONTENT_TYPE,
+            "application/javascript; charset=utf-8",
+        ))
+        .body(status::AIS_JS)
+}
+
 #[get("/ft8.js")]
 async fn ft8_js() -> impl Responder {
     HttpResponse::Ok()

src/trx-client/trx-frontend/trx-frontend-http/src/audio.rs

@@ -20,7 +20,7 @@ use bytes::Bytes;
 use tokio::sync::broadcast;
 use tracing::warn;
 
-use trx_core::decode::{AprsPacket, CwEvent, DecodedMessage, Ft8Message, WsprMessage};
+use trx_core::decode::{AisMessage, AprsPacket, CwEvent, DecodedMessage, Ft8Message, WsprMessage};
 use trx_frontend::FrontendRuntimeContext;
 
 const HISTORY_RETENTION: Duration = Duration::from_secs(24 * 60 * 60);
@@ -34,6 +34,24 @@ fn prune_aprs_history(history: &mut VecDeque<(Instant, AprsPacket)>) {
     }
 }
 
+fn prune_ais_history(history: &mut VecDeque<(Instant, AisMessage)>) {
+    while let Some((ts, _)) = history.front() {
+        if ts.elapsed() <= HISTORY_RETENTION {
+            break;
+        }
+        history.pop_front();
+    }
+}
+
+fn record_ais(context: &FrontendRuntimeContext, msg: AisMessage) {
+    let mut history = context
+        .ais_history
+        .lock()
+        .expect("ais history mutex poisoned");
+    history.push_back((Instant::now(), msg));
+    prune_ais_history(&mut history);
+}
+
 fn prune_cw_history(history: &mut VecDeque<(Instant, CwEvent)>) {
     while let Some((ts, _)) = history.front() {
         if ts.elapsed() <= HISTORY_RETENTION {
@@ -113,6 +131,22 @@ pub fn snapshot_aprs_history(context: &FrontendRuntimeContext) -> Vec<AprsPacket
         .collect()
 }
 
+pub fn snapshot_ais_history(context: &FrontendRuntimeContext) -> Vec<AisMessage> {
+    let mut history = context
+        .ais_history
+        .lock()
+        .expect("ais history mutex poisoned");
+    prune_ais_history(&mut history);
+    history
+        .iter()
+        .map(|(ts, msg)| {
+            let mut msg = msg.clone();
+            msg.ts_ms = Some(timestamp_ms_for_elapsed(ts.elapsed()));
+            msg
+        })
+        .collect()
+}
+
 pub fn snapshot_cw_history(context: &FrontendRuntimeContext) -> Vec<CwEvent> {
     let mut history = context
         .cw_history
@@ -148,6 +182,14 @@ pub fn clear_aprs_history(context: &FrontendRuntimeContext) {
     history.clear();
 }
 
+pub fn clear_ais_history(context: &FrontendRuntimeContext) {
+    let mut history = context
+        .ais_history
+        .lock()
+        .expect("ais history mutex poisoned");
+    history.clear();
+}
+
 fn timestamp_ms_for_elapsed(elapsed: Duration) -> i64 {
     let wall_clock = SystemTime::now()
         .checked_sub(elapsed)
@@ -206,6 +248,7 @@ pub fn start_decode_history_collector(context: Arc<FrontendRuntimeContext>) {
         loop {
             match rx.recv().await {
                 Ok(msg) => match msg {
+                    DecodedMessage::Ais(msg) => record_ais(&context, msg),
                     DecodedMessage::Aprs(pkt) => record_aprs(&context, pkt),
                     DecodedMessage::Cw(evt) => record_cw(&context, evt),
                     DecodedMessage::Ft8(msg) => record_ft8(&context, msg),

src/trx-client/trx-frontend/trx-frontend-http/src/status.rs

@@ -9,6 +9,7 @@ const CLIENT_BUILD_DATE: &str = env!("TRX_CLIENT_BUILD_DATE");
 const INDEX_HTML: &str = include_str!("../assets/web/index.html");
 pub const STYLE_CSS: &str = include_str!("../assets/web/style.css");
 pub const APP_JS: &str = include_str!("../assets/web/app.js");
+pub const AIS_JS: &str = include_str!("../assets/web/plugins/ais.js");
 pub const APRS_JS: &str = include_str!("../assets/web/plugins/aprs.js");
 pub const FT8_JS: &str = include_str!("../assets/web/plugins/ft8.js");
 pub const WSPR_JS: &str = include_str!("../assets/web/plugins/wspr.js");

src/trx-core/src/audio.rs

@@ -15,6 +15,7 @@ pub const AUDIO_MSG_APRS_DECODE: u8 = 0x03;
 pub const AUDIO_MSG_CW_DECODE: u8 = 0x04;
 pub const AUDIO_MSG_FT8_DECODE: u8 = 0x05;
 pub const AUDIO_MSG_WSPR_DECODE: u8 = 0x06;
+pub const AUDIO_MSG_AIS_DECODE: u8 = 0x07;
 
 /// Maximum payload size (1 MB) to reject bogus frames early.
 const MAX_PAYLOAD_SIZE: u32 = 1_048_576;

src/trx-core/src/decode.rs

@@ -2,7 +2,7 @@
 //
 // SPDX-License-Identifier: BSD-2-Clause
 
-//! Shared types for server-side decoded messages (APRS, CW).
+//! Shared types for server-side decoded messages (APRS, AIS, CW).
 
 use serde::{Deserialize, Serialize};
 
@@ -10,6 +10,8 @@ use serde::{Deserialize, Serialize};
 #[derive(Debug, Clone, Serialize, Deserialize)]
 #[serde(tag = "type")]
 pub enum DecodedMessage {
+    #[serde(rename = "ais")]
+    Ais(AisMessage),
     #[serde(rename = "aprs")]
     Aprs(AprsPacket),
     #[serde(rename = "cw")]
@@ -20,6 +22,37 @@ pub enum DecodedMessage {
     Wspr(WsprMessage),
 }
 
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AisMessage {
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub ts_ms: Option<i64>,
+    pub channel: String,
+    pub message_type: u8,
+    pub repeat: u8,
+    pub mmsi: u32,
+    pub crc_ok: bool,
+    pub bit_len: usize,
+    pub raw_bytes: Vec<u8>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub lat: Option<f64>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub lon: Option<f64>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub sog_knots: Option<f32>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub cog_deg: Option<f32>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub heading_deg: Option<u16>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub nav_status: Option<u8>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub vessel_name: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub callsign: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub destination: Option<String>,
+}
+
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct AprsPacket {
     #[serde(skip_serializing_if = "Option::is_none")]

src/trx-core/src/rig/mod.rs

@@ -72,6 +72,18 @@ pub trait AudioSource: Send + Sync {
     /// Subscribe to demodulated PCM audio from the primary channel.
     /// Returns a broadcast receiver that yields 20ms frames of mono f32 PCM.
     fn subscribe_pcm(&self) -> tokio::sync::broadcast::Receiver<Vec<f32>>;
+
+    /// Subscribe to PCM from a specific backend channel when available.
+    /// Channel `0` is always the primary channel.
+    fn subscribe_pcm_channel(&self, channel_idx: usize) -> tokio::sync::broadcast::Receiver<Vec<f32>> {
+        if channel_idx == 0 {
+            self.subscribe_pcm()
+        } else {
+            let (tx, rx) = tokio::sync::broadcast::channel(1);
+            drop(tx);
+            rx
+        }
+    }
 }
 
 /// Common interface for rig backends.

src/trx-core/src/rig/state.rs

@@ -70,6 +70,7 @@ pub enum RigMode {
     AM,
     WFM,
     FM,
+    AIS,
     DIG,
     PKT,
     Other(String),

src/trx-protocol/src/codec.rs

@@ -11,7 +11,7 @@ use trx_core::rig::state::RigMode;
 
 /// Parse a mode string into a RigMode.
 ///
-/// Handles LSB, USB, CW, CWR, AM, FM, WFM, DIG, DIGI, PKT, PACKET.
+/// Handles LSB, USB, CW, CWR, AM, FM, WFM, AIS, DIG, DIGI, PKT, PACKET.
 /// Falls back to Other(string) for unknown modes.
 pub fn parse_mode(s: &str) -> RigMode {
     match s.to_uppercase().as_str() {
@@ -22,6 +22,7 @@ pub fn parse_mode(s: &str) -> RigMode {
         "AM" => RigMode::AM,
         "FM" => RigMode::FM,
         "WFM" => RigMode::WFM,
+        "AIS" => RigMode::AIS,
         "DIG" | "DIGI" => RigMode::DIG,
         "PKT" | "PACKET" => RigMode::PKT,
         other => RigMode::Other(other.to_string()),
@@ -41,6 +42,7 @@ pub fn mode_to_string(mode: &RigMode) -> String {
         RigMode::AM => "AM".to_string(),
         RigMode::FM => "FM".to_string(),
         RigMode::WFM => "WFM".to_string(),
+        RigMode::AIS => "AIS".to_string(),
         RigMode::DIG => "DIG".to_string(),
         RigMode::PKT => "PKT".to_string(),
         RigMode::Other(s) => s.clone(),
@@ -78,6 +80,7 @@ mod tests {
         assert_eq!(parse_mode("AM"), RigMode::AM);
         assert_eq!(parse_mode("FM"), RigMode::FM);
         assert_eq!(parse_mode("WFM"), RigMode::WFM);
+        assert_eq!(parse_mode("AIS"), RigMode::AIS);
     }
 
     #[test]
@@ -122,6 +125,7 @@ mod tests {
         assert_eq!(mode_to_string(&RigMode::AM), "AM");
         assert_eq!(mode_to_string(&RigMode::FM), "FM");
         assert_eq!(mode_to_string(&RigMode::WFM), "WFM");
+        assert_eq!(mode_to_string(&RigMode::AIS), "AIS");
         assert_eq!(mode_to_string(&RigMode::DIG), "DIG");
         assert_eq!(mode_to_string(&RigMode::PKT), "PKT");
     }
@@ -141,6 +145,7 @@ mod tests {
             RigMode::AM,
             RigMode::FM,
             RigMode::WFM,
+            RigMode::AIS,
             RigMode::DIG,
             RigMode::PKT,
         ];

src/trx-server/Cargo.toml

@@ -27,6 +27,7 @@ cpal = "0.15"
 opus = "0.3"
 trx-app = { path = "../trx-app" }
 trx-backend = { path = "trx-backend", features = ["soapysdr"] }
+trx-ais = { path = "../decoders/trx-ais" }
 trx-core = { path = "../trx-core" }
 trx-aprs = { path = "../decoders/trx-aprs" }
 trx-cw = { path = "../decoders/trx-cw" }

src/trx-server/src/audio.rs

@@ -15,13 +15,14 @@ use tokio::net::{TcpListener, TcpStream};
 use tokio::sync::{broadcast, mpsc, watch};
 use tracing::{error, info, warn};
 
+use trx_ais::AisDecoder;
 use trx_aprs::AprsDecoder;
 use trx_core::audio::{
-    read_audio_msg, write_audio_msg, AudioStreamInfo, AUDIO_MSG_APRS_DECODE, AUDIO_MSG_CW_DECODE,
-    AUDIO_MSG_FT8_DECODE, AUDIO_MSG_RX_FRAME, AUDIO_MSG_STREAM_INFO, AUDIO_MSG_TX_FRAME,
-    AUDIO_MSG_WSPR_DECODE,
+    read_audio_msg, write_audio_msg, AudioStreamInfo, AUDIO_MSG_AIS_DECODE,
+    AUDIO_MSG_APRS_DECODE, AUDIO_MSG_CW_DECODE, AUDIO_MSG_FT8_DECODE, AUDIO_MSG_RX_FRAME,
+    AUDIO_MSG_STREAM_INFO, AUDIO_MSG_TX_FRAME, AUDIO_MSG_WSPR_DECODE,
 };
-use trx_core::decode::{AprsPacket, DecodedMessage, Ft8Message, WsprMessage};
+use trx_core::decode::{AisMessage, AprsPacket, DecodedMessage, Ft8Message, WsprMessage};
 use trx_core::rig::state::{RigMode, RigState};
 use trx_cw::CwDecoder;
 use trx_ft8::Ft8Decoder;
@@ -31,6 +32,7 @@ use crate::config::AudioConfig;
 use trx_decode_log::DecoderLoggers;
 
 const APRS_HISTORY_RETENTION: Duration = Duration::from_secs(24 * 60 * 60);
+const AIS_HISTORY_RETENTION: Duration = Duration::from_secs(24 * 60 * 60);
 const FT8_HISTORY_RETENTION: Duration = Duration::from_secs(24 * 60 * 60);
 const WSPR_HISTORY_RETENTION: Duration = Duration::from_secs(24 * 60 * 60);
 const FT8_SAMPLE_RATE: u32 = 12_000;
@@ -124,6 +126,7 @@ fn classify_stream_error(err: &str) -> &'static str {
 /// instance can maintain its own independent history.  Pass an
 /// `Arc<DecoderHistories>` into every decoder task and into the audio listener.
 pub struct DecoderHistories {
+    ais: Mutex<VecDeque<(Instant, AisMessage)>>,
     aprs: Mutex<VecDeque<(Instant, AprsPacket)>>,
     ft8: Mutex<VecDeque<(Instant, Ft8Message)>>,
     wspr: Mutex<VecDeque<(Instant, WsprMessage)>>,
@@ -132,12 +135,38 @@ pub struct DecoderHistories {
 impl DecoderHistories {
     pub fn new() -> Arc<Self> {
         Arc::new(Self {
+            ais: Mutex::new(VecDeque::new()),
             aprs: Mutex::new(VecDeque::new()),
             ft8: Mutex::new(VecDeque::new()),
             wspr: Mutex::new(VecDeque::new()),
         })
     }
 
+    // --- AIS ---
+
+    fn prune_ais(history: &mut VecDeque<(Instant, AisMessage)>) {
+        let cutoff = Instant::now() - AIS_HISTORY_RETENTION;
+        while let Some((ts, _)) = history.front() {
+            if *ts < cutoff {
+                history.pop_front();
+            } else {
+                break;
+            }
+        }
+    }
+
+    pub fn record_ais_message(&self, msg: AisMessage) {
+        let mut h = self.ais.lock().expect("ais history mutex poisoned");
+        h.push_back((Instant::now(), msg));
+        Self::prune_ais(&mut h);
+    }
+
+    pub fn snapshot_ais_history(&self) -> Vec<AisMessage> {
+        let mut h = self.ais.lock().expect("ais history mutex poisoned");
+        Self::prune_ais(&mut h);
+        h.iter().map(|(_, msg)| msg.clone()).collect()
+    }
+
     // --- APRS ---
 
     fn prune_aprs(history: &mut VecDeque<(Instant, AprsPacket)>) {
@@ -817,6 +846,104 @@ pub async fn run_aprs_decoder(
     }
 }
 
+fn downmix_if_needed(frame: Vec<f32>, channels: u16) -> Vec<f32> {
+    if channels <= 1 {
+        return frame;
+    }
+
+    let num_frames = frame.len() / channels as usize;
+    let mut mono = Vec::with_capacity(num_frames);
+    for i in 0..num_frames {
+        mono.push(frame[i * channels as usize]);
+    }
+    mono
+}
+
+/// Run the AIS decoder task. Only processes PCM when rig mode is AIS.
+pub async fn run_ais_decoder(
+    sample_rate: u32,
+    channels: u16,
+    mut pcm_a_rx: broadcast::Receiver<Vec<f32>>,
+    mut pcm_b_rx: broadcast::Receiver<Vec<f32>>,
+    mut state_rx: watch::Receiver<RigState>,
+    decode_tx: broadcast::Sender<DecodedMessage>,
+    histories: Arc<DecoderHistories>,
+) {
+    info!("AIS decoder started ({}Hz, {} ch)", sample_rate, channels);
+    let mut decoder_a = AisDecoder::new(sample_rate);
+    let mut decoder_b = AisDecoder::new(sample_rate);
+    let mut was_active = false;
+    let mut active = matches!(state_rx.borrow().status.mode, RigMode::AIS);
+
+    loop {
+        if !active {
+            match state_rx.changed().await {
+                Ok(()) => {
+                    let state = state_rx.borrow();
+                    active = matches!(state.status.mode, RigMode::AIS);
+                    if active {
+                        pcm_a_rx = pcm_a_rx.resubscribe();
+                        pcm_b_rx = pcm_b_rx.resubscribe();
+                    }
+                }
+                Err(_) => break,
+            }
+            continue;
+        }
+
+        tokio::select! {
+            recv = pcm_a_rx.recv() => {
+                match recv {
+                    Ok(frame) => {
+                        was_active = true;
+                        for msg in decoder_a.process_samples(&downmix_if_needed(frame, channels), "A") {
+                            histories.record_ais_message(msg.clone());
+                            let _ = decode_tx.send(DecodedMessage::Ais(msg));
+                        }
+                    }
+                    Err(broadcast::error::RecvError::Lagged(n)) => {
+                        warn!("AIS decoder A: dropped {} PCM frames", n);
+                    }
+                    Err(broadcast::error::RecvError::Closed) => break,
+                }
+            }
+            recv = pcm_b_rx.recv() => {
+                match recv {
+                    Ok(frame) => {
+                        was_active = true;
+                        for msg in decoder_b.process_samples(&downmix_if_needed(frame, channels), "B") {
+                            histories.record_ais_message(msg.clone());
+                            let _ = decode_tx.send(DecodedMessage::Ais(msg));
+                        }
+                    }
+                    Err(broadcast::error::RecvError::Lagged(n)) => {
+                        warn!("AIS decoder B: dropped {} PCM frames", n);
+                    }
+                    Err(broadcast::error::RecvError::Closed) => break,
+                }
+            }
+            changed = state_rx.changed() => {
+                match changed {
+                    Ok(()) => {
+                        let state = state_rx.borrow();
+                        active = matches!(state.status.mode, RigMode::AIS);
+                        if !active && was_active {
+                            decoder_a.reset();
+                            decoder_b.reset();
+                            was_active = false;
+                        }
+                        if active {
+                            pcm_a_rx = pcm_a_rx.resubscribe();
+                            pcm_b_rx = pcm_b_rx.resubscribe();
+                        }
+                    }
+                    Err(_) => break,
+                }
+            }
+        }
+    }
+}
+
 /// Run the CW decoder task. Only processes PCM when rig mode is CW or CWR.
 pub async fn run_cw_decoder(
     sample_rate: u32,
@@ -1332,6 +1459,15 @@ async fn handle_audio_client(
     let info_json = serde_json::to_vec(&stream_info).map_err(std::io::Error::other)?;
     write_audio_msg(&mut writer, AUDIO_MSG_STREAM_INFO, &info_json).await?;
 
+    // Send APRS history to newly connected client.
+    let history = histories.snapshot_ais_history();
+    for msg in history {
+        let msg = DecodedMessage::Ais(msg);
+        let msg_type = AUDIO_MSG_AIS_DECODE;
+        if let Ok(json) = serde_json::to_vec(&msg) {
+            write_audio_msg(&mut writer, msg_type, &json).await?;
+        }
+    }
     // Send APRS history to newly connected client.
     let history = histories.snapshot_aprs_history();
     for pkt in history {
@@ -1385,6 +1521,7 @@ async fn handle_audio_client(
                     match result {
                         Ok(msg) => {
                             let msg_type = match &msg {
+                                DecodedMessage::Ais(_) => AUDIO_MSG_AIS_DECODE,
                                 DecodedMessage::Aprs(_) => AUDIO_MSG_APRS_DECODE,
                                 DecodedMessage::Cw(_) => AUDIO_MSG_CW_DECODE,
                                 DecodedMessage::Ft8(_) => AUDIO_MSG_FT8_DECODE,

src/trx-server/src/main.rs

@@ -244,6 +244,7 @@ fn default_audio_bandwidth_for_mode(mode: &trx_core::rig::state::RigMode) -> u32
         RigMode::AM => 9_000,
         RigMode::FM => 12_500,
         RigMode::WFM => 180_000,
+        RigMode::AIS => 25_000,
         RigMode::Other(_) => 3_000,
     }
 }
@@ -264,6 +265,7 @@ fn parse_rig_mode(
         "AM" => RigMode::AM,
         "WFM" => RigMode::WFM,
         "FM" => RigMode::FM,
+        "AIS" => RigMode::AIS,
         "DIG" => RigMode::DIG,
         "PKT" => RigMode::PKT,
         _ => initial_mode.clone(),
@@ -274,10 +276,18 @@ fn parse_rig_mode(
 type SdrRigBuildResult = DynResult<(
     Box<dyn trx_core::rig::RigCat>,
     tokio::sync::broadcast::Receiver<Vec<f32>>,
+    (
+        tokio::sync::broadcast::Receiver<Vec<f32>>,
+        tokio::sync::broadcast::Receiver<Vec<f32>>,
+    ),
 )>;
 
 type OptionalSdrRig = Option<Box<dyn trx_core::rig::RigCat>>;
 type OptionalSdrPcmRx = Option<broadcast::Receiver<Vec<f32>>>;
+type OptionalSdrAisPcmRx = Option<(
+    broadcast::Receiver<Vec<f32>>,
+    broadcast::Receiver<Vec<f32>>,
+)>;
 
 /// Build a `SoapySdrRig` with full channel config from a `RigInstanceConfig`.
 #[cfg(feature = "soapysdr")]
@@ -312,6 +322,7 @@ fn build_sdr_rig_from_instance(rig_cfg: &RigInstanceConfig) -> SdrRigBuildResult
             64,
         ));
     }
+    let ais_channel_base_idx = channels.len();
 
     let sdr_rig = trx_backend::SoapySdrRig::new_with_config(
         args,
@@ -333,7 +344,11 @@ fn build_sdr_rig_from_instance(rig_cfg: &RigInstanceConfig) -> SdrRigBuildResult
     )?;
 
     let pcm_rx = sdr_rig.subscribe_pcm();
-    Ok((Box::new(sdr_rig) as Box<dyn trx_core::rig::RigCat>, pcm_rx))
+    let ais_pcm = (
+        sdr_rig.subscribe_pcm_channel(ais_channel_base_idx),
+        sdr_rig.subscribe_pcm_channel(ais_channel_base_idx + 1),
+    );
+    Ok((Box::new(sdr_rig) as Box<dyn trx_core::rig::RigCat>, pcm_rx, ais_pcm))
 }
 
 /// Build a `RigTaskConfig` for a single rig instance.
@@ -408,6 +423,10 @@ fn spawn_rig_audio_stack(
     longitude: Option<f64>,
     listen_override: Option<IpAddr>,
     sdr_pcm_rx: Option<broadcast::Receiver<Vec<f32>>>,
+    sdr_ais_pcm_rx: Option<(
+        broadcast::Receiver<Vec<f32>>,
+        broadcast::Receiver<Vec<f32>>,
+    )>,
 ) -> Vec<JoinHandle<()>> {
     let mut handles: Vec<JoinHandle<()>> = Vec::new();
 
@@ -593,6 +612,21 @@ fn spawn_rig_audio_stack(
             }
         }));
 
+        if let Some((ais_a_pcm_rx, ais_b_pcm_rx)) = sdr_ais_pcm_rx {
+            let ais_state_rx = state_rx.clone();
+            let ais_decode_tx = decode_tx.clone();
+            let ais_shutdown_rx = shutdown_rx.clone();
+            let ais_histories = histories.clone();
+            let ais_sr = rig_cfg.audio.sample_rate;
+            let ais_ch = rig_cfg.audio.channels as u16;
+            handles.push(tokio::spawn(async move {
+                tokio::select! {
+                    _ = audio::run_ais_decoder(ais_sr, ais_ch, ais_a_pcm_rx, ais_b_pcm_rx, ais_state_rx, ais_decode_tx, ais_histories) => {}
+                    _ = wait_for_shutdown(ais_shutdown_rx) => {}
+                }
+            }));
+        }
+
         // Spawn CW decoder task (no histories needed — CW has no persistent history)
         let cw_pcm_rx = pcm_tx.subscribe();
         let cw_state_rx = state_rx.clone();
@@ -819,16 +853,16 @@ async fn main() -> DynResult<()> {
 
         // Build SDR rig when applicable.
         #[cfg(feature = "soapysdr")]
-        let (sdr_prebuilt_rig, sdr_pcm_rx): (OptionalSdrRig, OptionalSdrPcmRx) =
+        let (sdr_prebuilt_rig, sdr_pcm_rx, sdr_ais_pcm_rx): (OptionalSdrRig, OptionalSdrPcmRx, OptionalSdrAisPcmRx) =
             if rig_cfg.rig.access.access_type.as_deref() == Some("sdr") {
-                let (rig, pcm_rx) = build_sdr_rig_from_instance(rig_cfg)?;
-                (Some(rig), Some(pcm_rx))
+                let (rig, pcm_rx, ais_pcm_rx) = build_sdr_rig_from_instance(rig_cfg)?;
+                (Some(rig), Some(pcm_rx), Some(ais_pcm_rx))
             } else {
-                (None, None)
+                (None, None, None)
             };
 
         #[cfg(not(feature = "soapysdr"))]
-        let (sdr_prebuilt_rig, sdr_pcm_rx): (OptionalSdrRig, OptionalSdrPcmRx) = (None, None);
+        let (sdr_prebuilt_rig, sdr_pcm_rx, sdr_ais_pcm_rx): (OptionalSdrRig, OptionalSdrPcmRx, OptionalSdrAisPcmRx) = (None, None, None);
 
         let histories = DecoderHistories::new();
 
@@ -889,6 +923,7 @@ async fn main() -> DynResult<()> {
             longitude,
             audio_listen_override,
             sdr_pcm_rx,
+            sdr_ais_pcm_rx,
         );
         task_handles.extend(audio_handles);
 

src/trx-server/src/rig_task.rs

@@ -773,7 +773,7 @@ fn map_signal_strength(mode: &RigMode, raw: u8) -> i32 {
     // FT-817 returns 0-15 for signal strength
     // Map to approximate dBm / S-units
     match mode {
-        RigMode::FM | RigMode::WFM => -120 + (raw as i32 * 6),
+        RigMode::FM | RigMode::WFM | RigMode::AIS => -120 + (raw as i32 * 6),
         _ => -127 + (raw as i32 * 6),
     }
 }

src/trx-server/trx-backend/src/dummy.rs

@@ -93,6 +93,7 @@ impl DummyRig {
                         RigMode::AM,
                         RigMode::FM,
                         RigMode::WFM,
+                        RigMode::AIS,
                         RigMode::DIG,
                         RigMode::PKT,
                     ],

src/trx-server/trx-backend/trx-backend-ft450d/src/lib.rs

@@ -164,6 +164,7 @@ impl Ft450d {
                     RigMode::AM,
                     RigMode::WFM,
                     RigMode::FM,
+                    RigMode::AIS,
                     RigMode::DIG,
                     RigMode::PKT,
                 ],
@@ -511,6 +512,7 @@ fn encode_mode(mode: &RigMode) -> DynResult<char> {
         RigMode::USB => Ok('2'),
         RigMode::CW => Ok('3'),
         RigMode::FM => Ok('4'),
+        RigMode::AIS => Ok('4'),
         RigMode::AM => Ok('5'),
         RigMode::DIG => Ok('6'),
         RigMode::CWR => Ok('7'),

src/trx-server/trx-backend/trx-backend-ft817/src/lib.rs

@@ -195,6 +195,7 @@ impl Ft817 {
                     RigMode::AM,
                     RigMode::WFM,
                     RigMode::FM,
+                    RigMode::AIS,
                     RigMode::DIG,
                     RigMode::PKT,
                 ],
@@ -588,6 +589,7 @@ fn encode_mode(mode: &RigMode) -> u8 {
         RigMode::AM => 0x04,
         RigMode::WFM => 0x06,
         RigMode::FM => 0x08,
+        RigMode::AIS => 0x08,
         RigMode::DIG => 0x0A,
         RigMode::PKT => 0x0C,
         RigMode::Other(_) => 0x00,

src/trx-server/trx-backend/trx-backend-soapysdr/src/demod.rs

@@ -156,6 +156,7 @@ impl Demodulator {
             RigMode::AM => Self::Am,
             RigMode::FM => Self::Fm,
             RigMode::WFM => Self::Wfm,
+            RigMode::AIS => Self::Fm,
             RigMode::CW | RigMode::CWR => Self::Cw,
             RigMode::DIG => Self::Passthrough,
             // VHF/UHF packet radio (APRS, AX.25) is FM-encoded AFSK.
@@ -187,6 +188,7 @@ mod tests {
         assert_eq!(Demodulator::for_mode(&RigMode::AM), Demodulator::Am);
         assert_eq!(Demodulator::for_mode(&RigMode::FM), Demodulator::Fm);
         assert_eq!(Demodulator::for_mode(&RigMode::WFM), Demodulator::Wfm);
+        assert_eq!(Demodulator::for_mode(&RigMode::AIS), Demodulator::Fm);
         assert_eq!(Demodulator::for_mode(&RigMode::CW), Demodulator::Cw);
         assert_eq!(Demodulator::for_mode(&RigMode::CWR), Demodulator::Cw);
         assert_eq!(

src/trx-server/trx-backend/trx-backend-soapysdr/src/dsp/channel.rs

@@ -23,6 +23,7 @@ fn iq_agc_for_mode(mode: &RigMode, sample_rate: u32) -> Option<SoftAgc> {
     let sr = sample_rate.max(1) as f32;
     match mode {
         RigMode::FM | RigMode::PKT => Some(SoftAgc::new(sr, 0.5, 150.0, 0.8, 12.0)),
+        RigMode::AIS => Some(SoftAgc::new(sr, 0.5, 150.0, 0.8, 12.0)),
         RigMode::WFM => None,
         _ => None,
     }
@@ -43,6 +44,7 @@ fn default_bandwidth_for_mode(mode: &RigMode) -> u32 {
         RigMode::AM => 9_000,
         RigMode::FM => 12_500,
         RigMode::WFM => 180_000,
+        RigMode::AIS => 25_000,
         RigMode::Other(_) => 3_000,
     }
 }

src/trx-server/trx-backend/trx-backend-soapysdr/src/lib.rs

@@ -17,6 +17,8 @@ use trx_core::rig::{
 };
 use trx_core::{DynResult, RigMode};
 
+const AIS_CHANNEL_SPACING_HZ: i64 = 50_000;
+
 /// RX-only backend for any SoapySDR-compatible device.
 pub struct SoapySdrRig {
     info: RigInfo,
@@ -47,9 +49,23 @@ pub struct SoapySdrRig {
     gain_db: f64,
     /// Optional hard ceiling for the applied hardware gain in dB.
     max_gain_db: Option<f64>,
+    /// Hidden AIS decoder channels (A and B) when available.
+    ais_channel_indices: Option<(usize, usize)>,
 }
 
 impl SoapySdrRig {
+    fn default_bandwidth_for_mode(mode: &RigMode) -> u32 {
+        match mode {
+            RigMode::LSB | RigMode::USB | RigMode::DIG => 3_000,
+            RigMode::PKT | RigMode::AIS => 25_000,
+            RigMode::CW | RigMode::CWR => 500,
+            RigMode::AM => 9_000,
+            RigMode::FM => 12_500,
+            RigMode::WFM => 180_000,
+            RigMode::Other(_) => 3_000,
+        }
+    }
+
     /// Full constructor.  All channel configuration is passed as plain
     /// parameters so this crate does not need to depend on `trx-server`
     /// (which is a binary, not a library crate).
@@ -130,6 +146,21 @@ impl SoapySdrRig {
             effective_gain_db,
         )?);
 
+        let primary_channel_count = channels.len();
+        let mut all_channels = channels.to_vec();
+        all_channels.push((
+            (initial_freq.hz as i64 - hardware_center_hz) as f64,
+            RigMode::FM,
+            25_000,
+            96,
+        ));
+        all_channels.push((
+            (initial_freq.hz as i64 + AIS_CHANNEL_SPACING_HZ - hardware_center_hz) as f64,
+            RigMode::FM,
+            25_000,
+            96,
+        ));
+
         let pipeline = dsp::SdrPipeline::start(
             iq_source,
             sdr_sample_rate,
@@ -138,7 +169,7 @@ impl SoapySdrRig {
             frame_duration_ms,
             wfm_deemphasis_us,
             true, // wfm_stereo: enabled by default
-            channels,
+            &all_channels,
         );
 
         let info = RigInfo {
@@ -160,6 +191,7 @@ impl SoapySdrRig {
                     RigMode::AM,
                     RigMode::WFM,
                     RigMode::FM,
+                    RigMode::AIS,
                     RigMode::DIG,
                     RigMode::PKT,
                 ],
@@ -209,6 +241,7 @@ impl SoapySdrRig {
             wfm_denoise: WfmDenoiseLevel::Auto,
             gain_db,
             max_gain_db,
+            ais_channel_indices: Some((primary_channel_count, primary_channel_count + 1)),
         })
     }
 
@@ -233,6 +266,36 @@ impl SoapySdrRig {
             0,         // center_offset_hz
         )
     }
+
+    fn update_ais_channel_offsets(&self) {
+        let Some((ais_a_idx, ais_b_idx)) = self.ais_channel_indices else {
+            return;
+        };
+
+        if let Some(dsp_arc) = self.pipeline.channel_dsps.get(ais_a_idx) {
+            let if_hz = (self.freq.hz as i64 - self.center_hz) as f64;
+            dsp_arc.lock().unwrap().set_channel_if_hz(if_hz);
+        }
+        if let Some(dsp_arc) = self.pipeline.channel_dsps.get(ais_b_idx) {
+            let if_hz = (self.freq.hz as i64 + AIS_CHANNEL_SPACING_HZ - self.center_hz) as f64;
+            dsp_arc.lock().unwrap().set_channel_if_hz(if_hz);
+        }
+    }
+
+    fn apply_ais_channel_filters(&self) {
+        let Some((ais_a_idx, ais_b_idx)) = self.ais_channel_indices else {
+            return;
+        };
+
+        for idx in [ais_a_idx, ais_b_idx] {
+            if let Some(dsp_arc) = self.pipeline.channel_dsps.get(idx) {
+                dsp_arc
+                    .lock()
+                    .unwrap()
+                    .set_filter(self.bandwidth_hz, self.fir_taps as usize);
+            }
+        }
+    }
 }
 
 // ---------------------------------------------------------------------------
@@ -251,7 +314,11 @@ impl Rig for SoapySdrRig {
 
 impl AudioSource for SoapySdrRig {
     fn subscribe_pcm(&self) -> tokio::sync::broadcast::Receiver<Vec<f32>> {
-        if let Some(sender) = self.pipeline.pcm_senders.get(self.primary_channel_idx) {
+        self.subscribe_pcm_channel(self.primary_channel_idx)
+    }
+
+    fn subscribe_pcm_channel(&self, channel_idx: usize) -> tokio::sync::broadcast::Receiver<Vec<f32>> {
+        if let Some(sender) = self.pipeline.pcm_senders.get(channel_idx) {
             sender.subscribe()
         } else {
             // No channels configured — return a receiver that will never
@@ -284,9 +351,14 @@ impl RigCat for SoapySdrRig {
             self.freq = freq;
             let half_span_hz = i128::from(self.pipeline.sdr_sample_rate) / 2;
             let current_center_hz = i128::from(self.center_hz);
-            let target_hz = i128::from(freq.hz);
-            let within_current_span = target_hz >= current_center_hz - half_span_hz
-                && target_hz <= current_center_hz + half_span_hz;
+            let target_lo_hz = i128::from(freq.hz);
+            let target_hi_hz = if self.mode == RigMode::AIS {
+                i128::from(freq.hz) + i128::from(AIS_CHANNEL_SPACING_HZ)
+            } else {
+                i128::from(freq.hz)
+            };
+            let within_current_span = target_lo_hz >= current_center_hz - half_span_hz
+                && target_hi_hz <= current_center_hz + half_span_hz;
 
             if !within_current_span {
                 // Only retune when the requested dial frequency leaves the
@@ -306,6 +378,7 @@ impl RigCat for SoapySdrRig {
                     dsp.reset_wfm_state();
                 }
             }
+            self.update_ais_channel_offsets();
             Ok(())
         })
     }
@@ -324,6 +397,7 @@ impl RigCat for SoapySdrRig {
                 let channel_if_hz = (self.freq.hz as i64 - self.center_hz) as f64;
                 dsp_arc.lock().unwrap().set_channel_if_hz(channel_if_hz);
             }
+            self.update_ais_channel_offsets();
             Ok(())
         })
     }
@@ -335,10 +409,14 @@ impl RigCat for SoapySdrRig {
         Box::pin(async move {
             tracing::debug!("SoapySdrRig: set_mode -> {:?}", mode);
             self.mode = mode.clone();
+            self.bandwidth_hz = Self::default_bandwidth_for_mode(&mode);
             // Update the primary channel's demodulator in the live pipeline.
             if let Some(dsp_arc) = self.pipeline.channel_dsps.get(self.primary_channel_idx) {
-                dsp_arc.lock().unwrap().set_mode(&mode);
+                let mut dsp = dsp_arc.lock().unwrap();
+                dsp.set_mode(&mode);
+                dsp.set_filter(self.bandwidth_hz, self.fir_taps as usize);
             }
+            self.apply_ais_channel_filters();
             Ok(())
         })
     }
@@ -490,6 +568,7 @@ impl RigCat for SoapySdrRig {
                     .unwrap()
                     .set_filter(bandwidth_hz, self.fir_taps as usize);
             }
+            self.apply_ais_channel_filters();
             Ok(())
         })
     }
@@ -507,6 +586,7 @@ impl RigCat for SoapySdrRig {
                     .unwrap()
                     .set_filter(self.bandwidth_hz, taps as usize);
             }
+            self.apply_ais_channel_filters();
             Ok(())
         })
     }