[feat](trx-rs): rename AMC (AM C-QUAM) to SAM (Stereo AM) with stereo width and carrier sync controls

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

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

@@ -2955,6 +2955,13 @@ function render(update) {
       wfmStFlagEl.classList.toggle("wfm-st-flag-stereo", detected);
       wfmStFlagEl.classList.toggle("wfm-st-flag-mono", !detected);
     }
+    if (samStereoWidthEl && typeof update.filter.sam_stereo_width === "number") {
+      samStereoWidthEl.value = String(Math.round(update.filter.sam_stereo_width * 100));
+    }
+    if (samCarrierSyncEl && typeof update.filter.sam_carrier_sync === "boolean") {
+      const nextVal = update.filter.sam_carrier_sync ? "on" : "off";
+      if (samCarrierSyncEl.value !== nextVal) samCarrierSyncEl.value = nextVal;
+    }
     const hasSdrSquelchEnabled = typeof update.filter.sdr_squelch_enabled === "boolean";
     const hasSdrSquelchThreshold = typeof update.filter.sdr_squelch_threshold_db === "number";
     if (hasSdrSquelchEnabled || hasSdrSquelchThreshold) {
@@ -3915,7 +3922,7 @@ const MODE_BW_DEFAULTS = {
   LSB:    [2_700,  300,   6_000,  100],
   USB:    [2_700,  300,   6_000,  100],
   AM:     [9_000,  500,   20_000, 500],
-  "AMC-QUAM": [9_000, 500, 20_000, 500],
+  SAM:    [9_000,  500,   20_000, 500],
   FM:     [12_500, 2_500, 25_000, 500],
   AIS:    [25_000, 12_500, 50_000, 500],
   VDES:   [100_000, 25_000, 200_000, 1_000],
@@ -7487,6 +7494,9 @@ const sdrLnaGainEl = document.getElementById("sdr-lna-gain-db");
 const sdrLnaGainSetBtn = document.getElementById("sdr-lna-gain-set");
 const sdrAgcEl = document.getElementById("sdr-agc-enabled");
 const wfmStFlagEl = document.getElementById("wfm-st-flag");
+const samControlsCol = document.getElementById("sam-controls-col");
+const samStereoWidthEl = document.getElementById("sam-stereo-width");
+const samCarrierSyncEl = document.getElementById("sam-carrier-sync");
 const sdrSquelchWrapEl = document.getElementById("sdr-squelch-wrap");
 const sdrSquelchEl = document.getElementById("sdr-squelch");
 const sdrSquelchPctEl = document.getElementById("sdr-squelch-pct");
@@ -7681,6 +7691,18 @@ if (wfmDeemphasisEl) {
     postPath(`/set_wfm_deemphasis?us=${encodeURIComponent(wfmDeemphasisEl.value)}`).catch(() => {});
   });
 }
+if (samStereoWidthEl) {
+  samStereoWidthEl.addEventListener("input", () => {
+    const width = Number(samStereoWidthEl.value) / 100;
+    postPath(`/set_sam_stereo_width?width=${width}`).catch(() => {});
+  });
+}
+if (samCarrierSyncEl) {
+  samCarrierSyncEl.addEventListener("change", () => {
+    const enabled = samCarrierSyncEl.value === "on";
+    postPath(`/set_sam_carrier_sync?enabled=${enabled}`).catch(() => {});
+  });
+}
 function submitSdrGain() {
   if (!sdrGainEl) return;
   const parsed = Number.parseFloat(sdrGainEl.value);
@@ -7761,9 +7783,9 @@ if (sdrNbThresholdEl) {
   });
 }
 function updateWfmControls() {
-  if (!wfmControlsCol) return;
   const mode = (modeEl && modeEl.value ? modeEl.value : "").toUpperCase();
-  wfmControlsCol.style.display = mode === "WFM" ? "" : "none";
+  if (wfmControlsCol) wfmControlsCol.style.display = mode === "WFM" ? "" : "none";
+  if (samControlsCol) samControlsCol.style.display = mode === "SAM" ? "" : "none";
 }
 
 // Show compatibility warning for non-Chromium browsers

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

@@ -253,6 +253,22 @@
                 </div>
                 <div class="label"><span>WFM</span></div>
               </div>
+              <div class="controls-col controls-col-sam label-below-col" id="sam-controls-col" style="display:none;">
+                <div class="inline sam-controls-inline">
+                  <label class="wfm-control">
+                    <span class="wfm-control-label">Stereo Width</span>
+                    <input type="range" id="sam-stereo-width" min="0" max="100" value="100" class="status-input" />
+                  </label>
+                  <label class="wfm-control">
+                    <span class="wfm-control-label">Carrier Sync</span>
+                    <select id="sam-carrier-sync" class="status-input">
+                      <option value="on">On</option>
+                      <option value="off">Off</option>
+                    </select>
+                  </label>
+                </div>
+                <div class="label"><span>SAM</span></div>
+              </div>
               <div class="controls-col controls-col-power label-below-col" id="tx-power-col">
                 <div class="label"><span>Transmit / Power</span></div>
                 <div class="btn-grid">
@@ -411,7 +427,7 @@
                 <option value="LSB">
                 <option value="USB">
                 <option value="AM">
-                <option value="AMC-QUAM">
+                <option value="SAM">
                 <option value="FM">
                 <option value="DIG">
                 <option value="CW">

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

@@ -1122,6 +1122,36 @@ pub async fn set_wfm_denoise(
     send_command(&rig_tx, RigCommand::SetWfmDenoise(q.level), q.remote).await
 }
 
+#[derive(serde::Deserialize)]
+pub struct SamStereoWidthQuery {
+    pub width: f32,
+    pub remote: Option<String>,
+}
+
+#[post("/set_sam_stereo_width")]
+pub async fn set_sam_stereo_width(
+    query: web::Query<SamStereoWidthQuery>,
+    rig_tx: web::Data<mpsc::Sender<RigRequest>>,
+) -> Result<HttpResponse, Error> {
+    let q = query.into_inner();
+    send_command(&rig_tx, RigCommand::SetSamStereoWidth(q.width), q.remote).await
+}
+
+#[derive(serde::Deserialize)]
+pub struct SamCarrierSyncQuery {
+    pub enabled: bool,
+    pub remote: Option<String>,
+}
+
+#[post("/set_sam_carrier_sync")]
+pub async fn set_sam_carrier_sync(
+    query: web::Query<SamCarrierSyncQuery>,
+    rig_tx: web::Data<mpsc::Sender<RigRequest>>,
+) -> Result<HttpResponse, Error> {
+    let q = query.into_inner();
+    send_command(&rig_tx, RigCommand::SetSamCarrierSync(q.enabled), q.remote).await
+}
+
 #[post("/toggle_aprs_decode")]
 pub async fn toggle_aprs_decode(
     query: web::Query<RemoteQuery>,
@@ -1974,6 +2004,8 @@ pub fn configure(cfg: &mut web::ServiceConfig) {
         .service(set_wfm_deemphasis)
         .service(set_wfm_stereo)
         .service(set_wfm_denoise)
+        .service(set_sam_stereo_width)
+        .service(set_sam_carrier_sync)
         .service(toggle_aprs_decode)
         .service(toggle_hf_aprs_decode)
         .service(toggle_cw_decode)

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

@@ -47,5 +47,7 @@ pub enum RigCommand {
     SetWfmDeemphasis(u32),
     SetWfmStereo(bool),
     SetWfmDenoise(WfmDenoiseLevel),
+    SetSamStereoWidth(f32),
+    SetSamCarrierSync(bool),
     GetSpectrum,
 }

src/trx-core/src/rig/controller/handlers.rs

@@ -529,6 +529,8 @@ pub fn command_from_rig_command(cmd: RigCommand) -> Box<dyn RigCommandHandler> {
         | RigCommand::SetWfmDeemphasis(_)
         | RigCommand::SetWfmStereo(_)
         | RigCommand::SetWfmDenoise(_)
+        | RigCommand::SetSamStereoWidth(_)
+        | RigCommand::SetSamCarrierSync(_)
         | RigCommand::GetSpectrum => Box::new(GetSnapshotCommand),
     }
 }

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

@@ -268,6 +268,26 @@ pub trait RigSdr: Send {
         )))
     }
 
+    fn set_sam_stereo_width<'a>(
+        &'a mut self,
+        _width: f32,
+    ) -> Pin<Box<dyn Future<Output = DynResult<()>> + Send + 'a>> {
+        Box::pin(std::future::ready(Err(
+            Box::new(response::RigError::not_supported("set_sam_stereo_width"))
+                as Box<dyn std::error::Error + Send + Sync>,
+        )))
+    }
+
+    fn set_sam_carrier_sync<'a>(
+        &'a mut self,
+        _enabled: bool,
+    ) -> Pin<Box<dyn Future<Output = DynResult<()>> + Send + 'a>> {
+        Box::pin(std::future::ready(Err(
+            Box::new(response::RigError::not_supported("set_sam_carrier_sync"))
+                as Box<dyn std::error::Error + Send + Sync>,
+        )))
+    }
+
     /// Return the current filter state if this backend supports filter controls.
     fn filter_state(&self) -> Option<state::RigFilterState> {
         None

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

@@ -87,8 +87,8 @@ pub enum RigMode {
     CW,
     CWR,
     AM,
-    /// AM C-QUAM stereo (Compatible Quadrature Amplitude Modulation).
+    /// Synchronous AM (Stereo AM) — carrier-locked stereo demodulation.
-    AMC,
+    SAM,
     WFM,
     FM,
     AIS,
@@ -338,6 +338,12 @@ pub struct RigFilterState {
     pub wfm_stereo_detected: bool,
     #[serde(default = "default_wfm_denoise_level")]
     pub wfm_denoise: WfmDenoiseLevel,
+    /// SAM stereo width (0.0 = mono, 1.0 = full stereo).
+    #[serde(default = "default_sam_stereo_width")]
+    pub sam_stereo_width: f32,
+    /// SAM carrier synchronization enabled.
+    #[serde(default = "default_sam_carrier_sync")]
+    pub sam_carrier_sync: bool,
 }
 
 #[derive(Debug, Clone, Copy, Serialize, Deserialize, PartialEq, Eq)]
@@ -358,6 +364,14 @@ fn default_wfm_stereo() -> bool {
     true
 }
 
+fn default_sam_stereo_width() -> f32 {
+    1.0
+}
+
+fn default_sam_carrier_sync() -> bool {
+    true
+}
+
 fn default_wfm_denoise_level() -> WfmDenoiseLevel {
     WfmDenoiseLevel::Auto
 }

src/trx-protocol/src/codec.rs

@@ -22,7 +22,7 @@ pub fn parse_mode(s: &str) -> RigMode {
         "CW" => RigMode::CW,
         "CWR" => RigMode::CWR,
         "AM" => RigMode::AM,
-        "AMC-QUAM" | "AMC_QUAM" | "AMC" => RigMode::AMC,
+        "SAM" | "AMC-QUAM" | "AMC_QUAM" | "AMC" => RigMode::SAM,
         "FM" => RigMode::FM,
         "WFM" => RigMode::WFM,
         "AIS" => RigMode::AIS,
@@ -45,7 +45,7 @@ pub fn mode_to_string(mode: &RigMode) -> Cow<'static, str> {
         RigMode::CW => Cow::Borrowed("CW"),
         RigMode::CWR => Cow::Borrowed("CWR"),
         RigMode::AM => Cow::Borrowed("AM"),
-        RigMode::AMC => Cow::Borrowed("AMC-QUAM"),
+        RigMode::SAM => Cow::Borrowed("SAM"),
         RigMode::FM => Cow::Borrowed("FM"),
         RigMode::WFM => Cow::Borrowed("WFM"),
         RigMode::AIS => Cow::Borrowed("AIS"),
@@ -85,7 +85,8 @@ mod tests {
         assert_eq!(parse_mode("CW"), RigMode::CW);
         assert_eq!(parse_mode("CWR"), RigMode::CWR);
         assert_eq!(parse_mode("AM"), RigMode::AM);
-        assert_eq!(parse_mode("AMC-QUAM"), RigMode::AMC);
+        assert_eq!(parse_mode("SAM"), RigMode::SAM);
+        assert_eq!(parse_mode("AMC-QUAM"), RigMode::SAM);
         assert_eq!(parse_mode("FM"), RigMode::FM);
         assert_eq!(parse_mode("WFM"), RigMode::WFM);
         assert_eq!(parse_mode("AIS"), RigMode::AIS);
@@ -132,7 +133,7 @@ mod tests {
         assert_eq!(mode_to_string(&RigMode::CW), "CW");
         assert_eq!(mode_to_string(&RigMode::CWR), "CWR");
         assert_eq!(mode_to_string(&RigMode::AM), "AM");
-        assert_eq!(mode_to_string(&RigMode::AMC), "AMC-QUAM");
+        assert_eq!(mode_to_string(&RigMode::SAM), "SAM");
         assert_eq!(mode_to_string(&RigMode::FM), "FM");
         assert_eq!(mode_to_string(&RigMode::WFM), "WFM");
         assert_eq!(mode_to_string(&RigMode::AIS), "AIS");
@@ -154,7 +155,7 @@ mod tests {
             RigMode::CW,
             RigMode::CWR,
             RigMode::AM,
-            RigMode::AMC,
+            RigMode::SAM,
             RigMode::FM,
             RigMode::WFM,
             RigMode::AIS,
@@ -325,6 +326,8 @@ mod tests {
                 wfm_stereo: true,
                 wfm_stereo_detected: false,
                 wfm_denoise: trx_core::WfmDenoiseLevel::Auto,
+                sam_stereo_width: 1.0,
+                sam_carrier_sync: true,
             }),
             ..minimal_snapshot()
         })
@@ -369,6 +372,8 @@ mod tests {
                 wfm_stereo: true,
                 wfm_stereo_detected: true,
                 wfm_denoise: trx_core::WfmDenoiseLevel::Auto,
+                sam_stereo_width: 0.5,
+                sam_carrier_sync: false,
             }),
             ..minimal_snapshot()
         };
@@ -379,6 +384,8 @@ mod tests {
         assert_eq!(f.sdr_gain_db, Some(18.0));
         assert_eq!(f.wfm_deemphasis_us, 50);
         assert!(f.wfm_stereo_detected);
+        assert_eq!(f.sam_stereo_width, 0.5);
+        assert!(!f.sam_carrier_sync);
     }
 
     fn minimal_snapshot() -> trx_core::rig::state::RigSnapshot {

src/trx-protocol/src/mapping.rs

@@ -73,6 +73,8 @@ pub fn client_command_to_rig(cmd: ClientCommand) -> RigCommand {
         }
         ClientCommand::SetWfmStereo { enabled } => RigCommand::SetWfmStereo(enabled),
         ClientCommand::SetWfmDenoise { level } => RigCommand::SetWfmDenoise(level),
+        ClientCommand::SetSamStereoWidth { width } => RigCommand::SetSamStereoWidth(width),
+        ClientCommand::SetSamCarrierSync { enabled } => RigCommand::SetSamCarrierSync(enabled),
         ClientCommand::GetSpectrum => RigCommand::GetSpectrum,
     }
 }
@@ -139,6 +141,8 @@ pub fn rig_command_to_client(cmd: RigCommand) -> ClientCommand {
         }
         RigCommand::SetWfmStereo(enabled) => ClientCommand::SetWfmStereo { enabled },
         RigCommand::SetWfmDenoise(level) => ClientCommand::SetWfmDenoise { level },
+        RigCommand::SetSamStereoWidth(width) => ClientCommand::SetSamStereoWidth { width },
+        RigCommand::SetSamCarrierSync(enabled) => ClientCommand::SetSamCarrierSync { enabled },
         RigCommand::GetSpectrum => ClientCommand::GetSpectrum,
     }
 }

src/trx-protocol/src/types.rs

@@ -52,6 +52,8 @@ pub enum ClientCommand {
     SetWfmDeemphasis { deemphasis_us: u32 },
     SetWfmStereo { enabled: bool },
     SetWfmDenoise { level: WfmDenoiseLevel },
+    SetSamStereoWidth { width: f32 },
+    SetSamCarrierSync { enabled: bool },
     GetSpectrum,
 }
 

src/trx-server/src/main.rs

@@ -239,7 +239,7 @@ fn default_audio_bandwidth_for_mode(mode: &trx_core::rig::state::RigMode) -> u32
         RigMode::LSB | RigMode::USB | RigMode::DIG => 3_000,
         RigMode::PKT => 25_000,
         RigMode::CW | RigMode::CWR => 500,
-        RigMode::AM | RigMode::AMC => 9_000,
+        RigMode::AM | RigMode::SAM => 9_000,
         RigMode::FM => 12_500,
         RigMode::WFM => 180_000,
         RigMode::AIS => 25_000,

src/trx-server/src/rig_task.rs

@@ -666,6 +666,38 @@ async fn process_command(
             let _ = ctx.state_tx.send(ctx.state.clone());
             return snapshot_from(ctx.state);
         }
+        RigCommand::SetSamStereoWidth(width) => {
+            if let Some(sdr) = ctx.rig.as_sdr() {
+                if let Err(e) = sdr.set_sam_stereo_width(width).await {
+                    return Err(RigError::communication(format!(
+                        "set_sam_stereo_width: {e}"
+                    )));
+                }
+            } else {
+                return Err(RigError::not_supported("set_sam_stereo_width"));
+            }
+            if let Some(f) = ctx.state.filter.as_mut() {
+                f.sam_stereo_width = width;
+            }
+            let _ = ctx.state_tx.send(ctx.state.clone());
+            return snapshot_from(ctx.state);
+        }
+        RigCommand::SetSamCarrierSync(enabled) => {
+            if let Some(sdr) = ctx.rig.as_sdr() {
+                if let Err(e) = sdr.set_sam_carrier_sync(enabled).await {
+                    return Err(RigError::communication(format!(
+                        "set_sam_carrier_sync: {e}"
+                    )));
+                }
+            } else {
+                return Err(RigError::not_supported("set_sam_carrier_sync"));
+            }
+            if let Some(f) = ctx.state.filter.as_mut() {
+                f.sam_carrier_sync = enabled;
+            }
+            let _ = ctx.state_tx.send(ctx.state.clone());
+            return snapshot_from(ctx.state);
+        }
         RigCommand::SetCenterFreq(freq) => {
             if let Some(sdr) = ctx.rig.as_sdr() {
                 if let Err(e) = sdr.set_center_freq(freq).await {

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

@@ -519,7 +519,7 @@ fn encode_mode(mode: &RigMode) -> DynResult<char> {
         RigMode::CWR => Ok('7'),
         RigMode::PKT => Ok('9'),
         RigMode::WFM => Ok('4'),
-        RigMode::AMC => Err("Unsupported mode for FT-450D".into()),
+        RigMode::SAM => Err("Unsupported mode for FT-450D".into()),
         RigMode::Other(_) => Err("Unsupported mode for FT-450D".into()),
     }
 }

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

@@ -603,7 +603,7 @@ fn encode_mode(mode: &RigMode) -> Option<u8> {
         RigMode::FM => 0x08,
         RigMode::DIG => 0x0A,
         RigMode::PKT => 0x0C,
-        RigMode::AIS | RigMode::VDES | RigMode::AMC | RigMode::Other(_) => return None,
+        RigMode::AIS | RigMode::VDES | RigMode::SAM | RigMode::Other(_) => return None,
     })
 }
 

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

@@ -3,18 +3,18 @@
 // SPDX-License-Identifier: BSD-2-Clause
 
 mod am;
-mod amcquam;
 mod fm;
 mod math;
 mod math_arm;
 mod math_x86;
+mod sam;
 mod ssb;
 mod wfm;
 
 use num_complex::Complex;
 use trx_core::rig::state::RigMode;
 
-pub use self::amcquam::CquamDemod;
+pub use self::sam::SamDemod;
 pub use self::wfm::WfmStereoDecoder;
 
 /// Shared DC blocker used by narrowband and WFM audio paths.
@@ -147,8 +147,8 @@ pub enum Demodulator {
     Cw,
     /// Pass-through (DIG, PKT): same as USB.
     Passthrough,
-    /// AM C-QUAM stereo: synchronous IQ detection with carrier phase tracking.
+    /// Synchronous AM (Stereo AM): carrier-locked IQ detection with stereo decode.
-    AmCQuam,
+    Sam,
 }
 
 impl Demodulator {
@@ -158,7 +158,7 @@ impl Demodulator {
             RigMode::USB => Self::Usb,
             RigMode::LSB => Self::Lsb,
             RigMode::AM => Self::Am,
-            RigMode::AMC => Self::AmCQuam,
+            RigMode::SAM => Self::Sam,
             RigMode::FM => Self::Fm,
             RigMode::WFM => Self::Wfm,
             RigMode::AIS | RigMode::VDES => Self::Fm,
@@ -175,7 +175,7 @@ impl Demodulator {
         match self {
             Self::Usb | Self::Passthrough => ssb::demod_usb(samples),
             Self::Lsb => ssb::demod_lsb(samples),
-            Self::Am | Self::AmCQuam => am::demod_am(samples),
+            Self::Am | Self::Sam => am::demod_am(samples),
             Self::Fm | Self::Wfm => fm::demod_fm(samples),
             Self::Cw => ssb::demod_cw(samples),
         }
@@ -201,7 +201,7 @@ mod tests {
             Demodulator::Passthrough
         );
         assert_eq!(Demodulator::for_mode(&RigMode::PKT), Demodulator::Fm);
-        assert_eq!(Demodulator::for_mode(&RigMode::AMC), Demodulator::AmCQuam);
+        assert_eq!(Demodulator::for_mode(&RigMode::SAM), Demodulator::Sam);
     }
 
     #[test]
@@ -215,7 +215,7 @@ mod tests {
             Demodulator::Wfm,
             Demodulator::Cw,
             Demodulator::Passthrough,
-            Demodulator::AmCQuam,
+            Demodulator::Sam,
         ];
         for demod in &demodulators {
             assert!(

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

@@ -1,126 +0,0 @@
-// SPDX-FileCopyrightText: 2026 Stan Grams <sjg@haxx.space>
-//
-// SPDX-License-Identifier: BSD-2-Clause
-
-use super::DcBlocker;
-use num_complex::Complex;
-
-/// C-QUAM (Compatible Quadrature AM) stereo demodulator.
-///
-/// Tracks the AM carrier phase using a first-order IIR filter on the baseband
-/// DC component (τ ≈ 50 ms), rotates each sample to align I with the sum
-/// audio and Q with the difference audio, then reconstructs L/R stereo.
-///
-/// Input: AGC-normalised baseband IQ samples at audio sample rate.
-/// Output: interleaved stereo PCM [L0, R0, L1, R1, …]
-pub struct CquamDemod {
-    /// IIR-tracked in-phase carrier estimate.
-    carrier_re: f32,
-    /// IIR-tracked quadrature carrier estimate.
-    carrier_im: f32,
-    /// IIR smoothing coefficient (close to 1 → slow tracking).
-    alpha: f32,
-    /// DC blocker for left channel output (removes the carrier-level DC).
-    dc_l: DcBlocker,
-    /// DC blocker for right channel output.
-    dc_r: DcBlocker,
-}
-
-impl CquamDemod {
-    /// Create a new C-QUAM demodulator for the given audio sample rate.
-    pub fn new(audio_sample_rate: u32) -> Self {
-        let sr = audio_sample_rate.max(1) as f32;
-        // 50 ms tracking time constant — slow enough not to follow audio
-        // modulation (lowest speech fundamental ~100 Hz → period 10 ms),
-        // fast enough to follow SDR frequency offset drift.
-        let alpha = (-1.0f32 / (0.05 * sr)).exp();
-        Self {
-            carrier_re: 1.0,
-            carrier_im: 0.0,
-            alpha,
-            dc_l: DcBlocker::new(0.999),
-            dc_r: DcBlocker::new(0.999),
-        }
-    }
-
-    /// Demodulate a block of AGC-normalised baseband IQ samples into
-    /// interleaved stereo audio.
-    pub fn demodulate_stereo(&mut self, samples: &[Complex<f32>]) -> Vec<f32> {
-        let mut out = Vec::with_capacity(samples.len() * 2);
-        let alpha = self.alpha;
-        let one_minus_alpha = 1.0 - alpha;
-
-        for &s in samples {
-            // Advance the carrier IIR tracker.  In steady state the DC
-            // component of s is the carrier phasor e^{jφ}.
-            self.carrier_re = alpha * self.carrier_re + one_minus_alpha * s.re;
-            self.carrier_im = alpha * self.carrier_im + one_minus_alpha * s.im;
-
-            // Rotate s by −φ to phase-align I with (1 + m_s) and Q with m_d.
-            let mag_sq = self.carrier_re * self.carrier_re + self.carrier_im * self.carrier_im;
-            let (i_corr, q_corr) = if mag_sq > 1e-8 {
-                let inv = mag_sq.sqrt().recip();
-                let cos_phi = self.carrier_re * inv;
-                let sin_phi = self.carrier_im * inv;
-                // s · e^{-jφ}
-                (
-                    s.re * cos_phi + s.im * sin_phi,
-                    -s.re * sin_phi + s.im * cos_phi,
-                )
-            } else {
-                (s.re, s.im)
-            };
-
-            // Stereo decode.
-            // I ≈ 1 + (L+R)/2,  Q ≈ (L−R)/2
-            // L_raw = I + Q = 1 + L  →  DC-block → L audio
-            // R_raw = I − Q = 1 + R  →  DC-block → R audio
-            out.push(self.dc_l.process(i_corr + q_corr));
-            out.push(self.dc_r.process(i_corr - q_corr));
-        }
-        out
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn test_cquam_silence_is_silent() {
-        let mut demod = CquamDemod::new(8_000);
-        let samples = vec![Complex::new(0.0f32, 0.0); 256];
-        let out = demod.demodulate_stereo(&samples);
-        assert_eq!(out.len(), 512);
-        for &s in &out {
-            assert!(
-                s.abs() < 1e-5,
-                "silence should produce near-zero output, got {s}"
-            );
-        }
-    }
-
-    #[test]
-    fn test_cquam_pure_am_mono() {
-        // A pure AM carrier (no Q modulation) should produce equal L and R.
-        let mut demod = CquamDemod::new(8_000);
-        // Let the carrier tracker settle for 1 s worth of samples.
-        let settle: Vec<Complex<f32>> = (0..8_000)
-            .map(|i| {
-                let t = i as f32 / 8_000.0;
-                let audio = 0.5 * (2.0 * std::f32::consts::PI * 440.0 * t).sin();
-                Complex::new(1.0 + audio, 0.0)
-            })
-            .collect();
-        let out = demod.demodulate_stereo(&settle);
-        // After settling, L and R should be roughly equal (within 0.02 amplitude).
-        for chunk in out.chunks_exact(2).skip(4_000) {
-            let l = chunk[0];
-            let r = chunk[1];
-            assert!(
-                (l - r).abs() < 0.02,
-                "pure AM mono should have L ≈ R, got L={l:.4} R={r:.4}"
-            );
-        }
-    }
-}

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

@@ -0,0 +1,182 @@
+// SPDX-FileCopyrightText: 2026 Stan Grams <sjg@haxx.space>
+//
+// SPDX-License-Identifier: BSD-2-Clause
+
+use super::DcBlocker;
+use num_complex::Complex;
+
+/// Synchronous AM (Stereo AM) demodulator with carrier synchronization.
+///
+/// Tracks the AM carrier phase using a first-order IIR filter on the baseband
+/// DC component (τ ≈ 50 ms), rotates each sample to align I with the sum
+/// audio and Q with the difference audio, then reconstructs L/R stereo.
+///
+/// `stereo_width` controls the L/R separation (0.0 = mono, 1.0 = full stereo).
+/// `carrier_sync` enables/disables the carrier phase tracking PLL.
+///
+/// Input: AGC-normalised baseband IQ samples at audio sample rate.
+/// Output: interleaved stereo PCM [L0, R0, L1, R1, …]
+pub struct SamDemod {
+    /// IIR-tracked in-phase carrier estimate.
+    carrier_re: f32,
+    /// IIR-tracked quadrature carrier estimate.
+    carrier_im: f32,
+    /// IIR smoothing coefficient (close to 1 → slow tracking).
+    alpha: f32,
+    /// DC blocker for left channel output (removes the carrier-level DC).
+    dc_l: DcBlocker,
+    /// DC blocker for right channel output.
+    dc_r: DcBlocker,
+    /// Stereo width: 0.0 = mono, 1.0 = full stereo separation.
+    stereo_width: f32,
+    /// Whether carrier phase synchronization is active.
+    carrier_sync: bool,
+}
+
+impl SamDemod {
+    /// Create a new SAM demodulator for the given audio sample rate.
+    pub fn new(audio_sample_rate: u32) -> Self {
+        let sr = audio_sample_rate.max(1) as f32;
+        // 50 ms tracking time constant — slow enough not to follow audio
+        // modulation (lowest speech fundamental ~100 Hz → period 10 ms),
+        // fast enough to follow SDR frequency offset drift.
+        let alpha = (-1.0f32 / (0.05 * sr)).exp();
+        Self {
+            carrier_re: 1.0,
+            carrier_im: 0.0,
+            alpha,
+            dc_l: DcBlocker::new(0.999),
+            dc_r: DcBlocker::new(0.999),
+            stereo_width: 1.0,
+            carrier_sync: true,
+        }
+    }
+
+    /// Set stereo width (0.0 = mono, 1.0 = full stereo).
+    pub fn set_stereo_width(&mut self, width: f32) {
+        self.stereo_width = width.clamp(0.0, 1.0);
+    }
+
+    /// Enable or disable carrier phase synchronization.
+    pub fn set_carrier_sync(&mut self, enabled: bool) {
+        self.carrier_sync = enabled;
+        if !enabled {
+            // Reset carrier tracker to default (real axis aligned).
+            self.carrier_re = 1.0;
+            self.carrier_im = 0.0;
+        }
+    }
+
+    /// Demodulate a block of AGC-normalised baseband IQ samples into
+    /// interleaved stereo audio.
+    pub fn demodulate_stereo(&mut self, samples: &[Complex<f32>]) -> Vec<f32> {
+        let mut out = Vec::with_capacity(samples.len() * 2);
+        let alpha = self.alpha;
+        let one_minus_alpha = 1.0 - alpha;
+        let w = self.stereo_width;
+
+        for &s in samples {
+            let (i_corr, q_corr) = if self.carrier_sync {
+                // Advance the carrier IIR tracker.  In steady state the DC
+                // component of s is the carrier phasor e^{jφ}.
+                self.carrier_re = alpha * self.carrier_re + one_minus_alpha * s.re;
+                self.carrier_im = alpha * self.carrier_im + one_minus_alpha * s.im;
+
+                // Rotate s by −φ to phase-align I with (1 + m_s) and Q with m_d.
+                let mag_sq = self.carrier_re * self.carrier_re + self.carrier_im * self.carrier_im;
+                if mag_sq > 1e-8 {
+                    let inv = mag_sq.sqrt().recip();
+                    let cos_phi = self.carrier_re * inv;
+                    let sin_phi = self.carrier_im * inv;
+                    // s · e^{-jφ}
+                    (
+                        s.re * cos_phi + s.im * sin_phi,
+                        -s.re * sin_phi + s.im * cos_phi,
+                    )
+                } else {
+                    (s.re, s.im)
+                }
+            } else {
+                // No carrier sync — treat I/Q as-is (envelope detection).
+                (s.re, s.im)
+            };
+
+            // Stereo decode.
+            // I ≈ 1 + (L+R)/2,  Q ≈ (L−R)/2
+            // L_raw = I + w*Q = 1 + L  →  DC-block → L audio
+            // R_raw = I − w*Q = 1 + R  →  DC-block → R audio
+            let l = self.dc_l.process(i_corr + w * q_corr);
+            let r = self.dc_r.process(i_corr - w * q_corr);
+            out.push(l);
+            out.push(r);
+        }
+        out
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_sam_silence_is_silent() {
+        let mut demod = SamDemod::new(8_000);
+        let samples = vec![Complex::new(0.0f32, 0.0); 256];
+        let out = demod.demodulate_stereo(&samples);
+        assert_eq!(out.len(), 512);
+        for &s in &out {
+            assert!(
+                s.abs() < 1e-5,
+                "silence should produce near-zero output, got {s}"
+            );
+        }
+    }
+
+    #[test]
+    fn test_sam_pure_am_mono() {
+        // A pure AM carrier (no Q modulation) should produce equal L and R.
+        let mut demod = SamDemod::new(8_000);
+        // Let the carrier tracker settle for 1 s worth of samples.
+        let settle: Vec<Complex<f32>> = (0..8_000)
+            .map(|i| {
+                let t = i as f32 / 8_000.0;
+                let audio = 0.5 * (2.0 * std::f32::consts::PI * 440.0 * t).sin();
+                Complex::new(1.0 + audio, 0.0)
+            })
+            .collect();
+        let out = demod.demodulate_stereo(&settle);
+        // After settling, L and R should be roughly equal (within 0.02 amplitude).
+        for chunk in out.chunks_exact(2).skip(4_000) {
+            let l = chunk[0];
+            let r = chunk[1];
+            assert!(
+                (l - r).abs() < 0.02,
+                "pure AM mono should have L ≈ R, got L={l:.4} R={r:.4}"
+            );
+        }
+    }
+
+    #[test]
+    fn test_sam_stereo_width_zero_is_mono() {
+        let mut demod = SamDemod::new(8_000);
+        demod.set_stereo_width(0.0);
+        // Feed carrier with Q modulation — should still be mono.
+        let samples: Vec<Complex<f32>> = (0..8_000)
+            .map(|i| {
+                let t = i as f32 / 8_000.0;
+                let audio = 0.3 * (2.0 * std::f32::consts::PI * 1000.0 * t).sin();
+                Complex::new(1.0, audio)
+            })
+            .collect();
+        let out = demod.demodulate_stereo(&samples);
+        // With width=0, L and R should be identical.
+        for chunk in out.chunks_exact(2).skip(4_000) {
+            let l = chunk[0];
+            let r = chunk[1];
+            assert!(
+                (l - r).abs() < 1e-5,
+                "width=0 should produce identical L/R, got L={l:.4} R={r:.4}"
+            );
+        }
+    }
+}

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

@@ -6,7 +6,7 @@ use num_complex::Complex;
 use tokio::sync::broadcast;
 use trx_core::rig::state::{RdsData, RigMode, WfmDenoiseLevel};
 
-use crate::demod::{CquamDemod, DcBlocker, Demodulator, SoftAgc, WfmStereoDecoder};
+use crate::demod::{DcBlocker, Demodulator, SamDemod, SoftAgc, WfmStereoDecoder};
 
 use super::{BlockFirFilterPair, IQ_BLOCK_SIZE};
 
@@ -196,7 +196,7 @@ fn agc_for_mode(mode: &RigMode, audio_sample_rate: u32) -> SoftAgc {
     let sr = audio_sample_rate.max(1) as f32;
     match mode {
         RigMode::CW | RigMode::CWR => SoftAgc::new(sr, 1.0, 50.0, 0.5, 30.0),
-        RigMode::AM | RigMode::AMC => SoftAgc::new(sr, 5.0, 200.0, 0.5, 36.0),
+        RigMode::AM | RigMode::SAM => SoftAgc::new(sr, 5.0, 200.0, 0.5, 36.0),
         _ => SoftAgc::new(sr, 5.0, 500.0, 0.5, 30.0),
     }
 }
@@ -210,7 +210,7 @@ fn iq_agc_for_mode(mode: &RigMode, sample_rate: u32) -> Option<SoftAgc> {
         // DC blocker always sees the same steady-state bias (~0.7) regardless
         // of RF signal strength.  Fast attack (0.5 ms) catches sudden carrier
         // appearance; 50 ms release tracks slow fading without distorting audio.
-        RigMode::AM | RigMode::AMC => Some(SoftAgc::new(sr, 0.5, 50.0, 0.7, 30.0)),
+        RigMode::AM | RigMode::SAM => Some(SoftAgc::new(sr, 0.5, 50.0, 0.7, 30.0)),
         RigMode::WFM => None,
         _ => None,
     }
@@ -219,8 +219,8 @@ fn iq_agc_for_mode(mode: &RigMode, sample_rate: u32) -> Option<SoftAgc> {
 fn dc_for_mode(mode: &RigMode) -> Option<DcBlocker> {
     match mode {
         RigMode::WFM => None,
-        // AMC: DC is handled inside CquamDemod per channel (L and R separately).
+        // SAM: DC is handled inside SamDemod per channel (L and R separately).
-        RigMode::AMC => None,
+        RigMode::SAM => None,
         // AM: the envelope detector output has a large carrier-amplitude DC
         // bias (A_c).  r=0.999 gives τ≈125 ms at 8 kHz, tracking carrier
         // level ~10× faster than r=0.9999 while still passing all audio
@@ -235,7 +235,7 @@ fn default_bandwidth_for_mode(mode: &RigMode) -> u32 {
         RigMode::LSB | RigMode::USB | RigMode::DIG => 3_000,
         RigMode::PKT => 25_000,
         RigMode::CW | RigMode::CWR => 500,
-        RigMode::AM | RigMode::AMC => 9_000,
+        RigMode::AM | RigMode::SAM => 9_000,
         RigMode::FM => 12_500,
         RigMode::WFM => 180_000,
         RigMode::AIS => 25_000,
@@ -288,7 +288,7 @@ pub struct ChannelDsp {
     resample_phase: f64,
     resample_phase_inc: f64,
     wfm_decoder: Option<WfmStereoDecoder>,
-    cquam_decoder: Option<CquamDemod>,
+    sam_decoder: Option<SamDemod>,
     iq_agc: Option<SoftAgc>,
     audio_agc: SoftAgc,
     audio_dc: Option<DcBlocker>,
@@ -301,9 +301,9 @@ pub struct ChannelDsp {
 impl ChannelDsp {
     fn clamp_bandwidth_for_mode(mode: &RigMode, bandwidth_hz: u32) -> u32 {
         match mode {
-            // C-QUAM requires ≥ 9 kHz to capture both sum (L+R) and difference
+            // SAM stereo requires ≥ 9 kHz to capture both sum (L+R) and difference
             // (L−R) sidebands; narrower bandwidths would discard stereo content.
-            RigMode::AMC => bandwidth_hz.max(9_000),
+            RigMode::SAM => bandwidth_hz.max(9_000),
             _ => bandwidth_hz,
         }
     }
@@ -385,10 +385,10 @@ impl ChannelDsp {
         } else {
             self.wfm_decoder = None;
         }
-        if self.mode == RigMode::AMC {
+        if self.mode == RigMode::SAM {
-            self.cquam_decoder = Some(CquamDemod::new(self.audio_sample_rate));
+            self.sam_decoder = Some(SamDemod::new(self.audio_sample_rate));
         } else {
-            self.cquam_decoder = None;
+            self.sam_decoder = None;
         }
         self.iq_agc = iq_agc_for_mode(&self.mode, channel_sample_rate);
         self.audio_agc = agc_for_mode(&self.mode, self.audio_sample_rate);
@@ -488,8 +488,8 @@ impl ChannelDsp {
             } else {
                 None
             },
-            cquam_decoder: if *mode == RigMode::AMC {
+            sam_decoder: if *mode == RigMode::SAM {
-                Some(CquamDemod::new(audio_sample_rate))
+                Some(SamDemod::new(audio_sample_rate))
             } else {
                 None
             },
@@ -548,6 +548,18 @@ impl ChannelDsp {
         }
     }
 
+    pub fn set_sam_stereo_width(&mut self, width: f32) {
+        if let Some(decoder) = &mut self.sam_decoder {
+            decoder.set_stereo_width(width);
+        }
+    }
+
+    pub fn set_sam_carrier_sync(&mut self, enabled: bool) {
+        if let Some(decoder) = &mut self.sam_decoder {
+            decoder.set_carrier_sync(enabled);
+        }
+    }
+
     pub fn set_wfm_denoise(&mut self, level: WfmDenoiseLevel) {
         self.wfm_denoise = level;
         if let Some(decoder) = &mut self.wfm_decoder {
@@ -709,7 +721,7 @@ impl ChannelDsp {
                 *sample = (*sample * WFM_OUTPUT_GAIN).clamp(-1.0, 1.0);
             }
             out
-        } else if let Some(decoder) = self.cquam_decoder.as_mut() {
+        } else if let Some(decoder) = self.sam_decoder.as_mut() {
             let stereo = decoder.demodulate_stereo(decimated);
             // Apply stereo-aware AGC (shared gain preserves L/R balance).
             let mut out = Vec::with_capacity(stereo.len());

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

@@ -48,6 +48,10 @@ pub struct SoapySdrRig {
     wfm_stereo: bool,
     /// Whether WFM stereo denoise is enabled.
     wfm_denoise: WfmDenoiseLevel,
+    /// SAM stereo width (0.0 = mono, 1.0 = full stereo).
+    sam_stereo_width: f32,
+    /// SAM carrier synchronization enabled.
+    sam_carrier_sync: bool,
     /// Requested hardware gain setting in dB.
     gain_db: f64,
     /// Optional hard ceiling for the applied hardware gain in dB.
@@ -77,7 +81,7 @@ impl SoapySdrRig {
             RigMode::PKT | RigMode::AIS => 25_000,
             RigMode::VDES => 100_000,
             RigMode::CW | RigMode::CWR => 500,
-            RigMode::AM | RigMode::AMC => 9_000,
+            RigMode::AM | RigMode::SAM => 9_000,
             RigMode::FM => 12_500,
             RigMode::WFM => 180_000,
             RigMode::Other(_) => 3_000,
@@ -251,7 +255,7 @@ impl SoapySdrRig {
                     RigMode::CW,
                     RigMode::CWR,
                     RigMode::AM,
-                    RigMode::AMC,
+                    RigMode::SAM,
                     RigMode::WFM,
                     RigMode::FM,
                     RigMode::AIS,
@@ -311,6 +315,8 @@ impl SoapySdrRig {
             wfm_deemphasis_us,
             wfm_stereo: true,
             wfm_denoise: WfmDenoiseLevel::Auto,
+            sam_stereo_width: 1.0,
+            sam_carrier_sync: true,
             gain_db,
             max_gain_db,
             lna_gain_db: initial_lna_gain_db,
@@ -856,6 +862,38 @@ impl RigSdr for SoapySdrRig {
         })
     }
 
+    fn set_sam_stereo_width<'a>(
+        &'a mut self,
+        width: f32,
+    ) -> Pin<Box<dyn std::future::Future<Output = DynResult<()>> + Send + 'a>> {
+        Box::pin(async move {
+            self.sam_stereo_width = width.clamp(0.0, 1.0);
+            {
+                let dsps = self.pipeline.channel_dsps.read().unwrap();
+                if let Some(dsp_arc) = dsps.get(self.primary_channel_idx) {
+                    dsp_arc.lock().unwrap().set_sam_stereo_width(width);
+                }
+            }
+            Ok(())
+        })
+    }
+
+    fn set_sam_carrier_sync<'a>(
+        &'a mut self,
+        enabled: bool,
+    ) -> Pin<Box<dyn std::future::Future<Output = DynResult<()>> + Send + 'a>> {
+        Box::pin(async move {
+            self.sam_carrier_sync = enabled;
+            {
+                let dsps = self.pipeline.channel_dsps.read().unwrap();
+                if let Some(dsp_arc) = dsps.get(self.primary_channel_idx) {
+                    dsp_arc.lock().unwrap().set_sam_carrier_sync(enabled);
+                }
+            }
+            Ok(())
+        })
+    }
+
     fn filter_state(&self) -> Option<RigFilterState> {
         let wfm_stereo_detected = self
             .pipeline
@@ -883,6 +921,8 @@ impl RigSdr for SoapySdrRig {
             wfm_stereo: self.wfm_stereo,
             wfm_stereo_detected,
             wfm_denoise: self.wfm_denoise,
+            sam_stereo_width: self.sam_stereo_width,
+            sam_carrier_sync: self.sam_carrier_sync,
         })
     }
 

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

@@ -43,7 +43,7 @@ fn default_bandwidth_hz(mode: &RigMode) -> u32 {
     match mode {
         RigMode::CW | RigMode::CWR => 500,
         RigMode::LSB | RigMode::USB | RigMode::DIG => 3_000,
-        RigMode::AM | RigMode::AMC => 9_000,
+        RigMode::AM | RigMode::SAM => 9_000,
         RigMode::FM => 12_500,
         RigMode::WFM => 180_000,
         RigMode::PKT | RigMode::AIS => 25_000,