feat(cw): add built-in CW Morse code decoder for linear transponders

- Add CwDsp with FIR bandpass filter, envelope detection, Goertzel tone detector
- Add CwDecoder with real-time Morse timing analysis and character lookup
- Add CW state/actions to RadarState, wire into RadarViewModel
- Add collapsible CW decoder panel to transceivers page
- 19 unit tests covering DSP, Morse table, and decoder state
- Shares IAudioCapture with SSTV, auto-stops SSTV when CW starts

.hermes/plans/2026-07-31_113800-cw-decoder-implementation.md

@@ -0,0 +1,781 @@
+# CW Morse Code Decoder — Implementation Plan
+
+> **For Hermes:** Use subagent-driven-development skill to implement this plan task-by-task.
+
+**Goal:** Add a built-in Morse Code (CW) decoder to the Look4Sat linear satellite transceiver interface. Captures audio from the microphone, decodes CW in real-time, and displays the decoded text inline without blocking existing features.
+
+**Architecture:** Domain layer DSP (bandpass filter + envelope detection + timing logic) mirrors the existing `SstvDecoder` pattern. State managed in `RadarState` / `RadarViewModel`. UI is a compact collapsible panel inside the `TransceiverItem` expanded card, below the Doppler calculator, using the same `IAudioCapture` abstraction for microphone access.
+
+**Tech Stack:** Kotlin, Jetpack Compose, Android AudioRecord (via existing `IAudioCapture`), pure Kotlin DSP (no NDK), `kotlinx.coroutines.flow`.
+
+---
+
+## Current Context
+
+The app already has:
+- **`IAudioCapture`** (`core/domain/.../usecase/IAudioCapture.kt`) — platform abstraction for microphone audio capture, emits `Flow<FloatArray>` at configurable sample rate
+- **`SstvDecoder`** (`core/domain/.../sstv/SstvDecoder.kt`) — full audio→image decoder for SSTV, the architectural pattern to follow
+- **`SstvDsp`** (`core/domain/.../sstv/SstvDsp.kt`) — DSP utilities (FFT, window functions, filters) — reusable for CW
+- **`RadarViewModel`** — manages SSTV lifecycle (init decoder, start/stop recording, handle permission)
+- **`TransceiversPage.kt`** — expanded transceiver card with Doppler calculator already added
+- **`RadarState.kt`** — `SstvSubState` pattern to follow for CW substate
+
+**CW decoding pipeline (audio → text):**
+```
+Audio buffer → Bandpass filter (~600-800 Hz) → Envelope detection → Threshold → 
+Timing (dit/dash/symbol/word gaps) → Morse character lookup → Live text output
+```
+
+**Key frequencies:**
+- CW tone: typically 600-800 Hz (user-selectable)
+- Sampling rate: 8000 Hz (reuse from SSTV, adequate for ~1 kHz bandwidth)
+- Dit timing: 30-60 ms at typical 20-30 WPM (auto-baud rate detection)
+
+---
+
+## Step-by-step Plan
+
+### Task 1: Create CW decoder DSP (domain layer)
+
+**Objective:** Implement the core CW signal processing: bandpass filter, envelope detection, and timing logic to convert audio samples to dit/dash symbols.
+
+**Files:**
+- Create: `core/domain/src/main/java/com/rtbishop/look4sat/core/domain/cw/CwDsp.kt`
+- Create: `core/domain/src/main/java/com/rtbishop/look4sat/core/domain/cw/CwDecoder.kt`
+- Modify: `core/domain/build.gradle.kts` (no changes needed — pure Kotlin)
+
+**Step 1: Create `CwDsp.kt` — DSP utilities for CW decoding**
+
+```kotlin
+package com.rtbishop.look4sat.core.domain.cw
+
+import kotlin.math.PI
+import kotlin.math.cos
+import kotlin.math.exp
+import kotlin.math.log10
+import kotlin.math.sqrt
+
+/**
+ * DSP utilities for CW (Morse code) decoding.
+ * Pure Kotlin, no NDK required.
+ */
+internal object CwDsp {
+
+    /**
+     * Design a simple bandpass FIR filter coefficients using windowed sinc method.
+     * @param lowCutoff  lower cutoff frequency (Hz) as fraction of sampleRate
+     * @param highCutoff upper cutoff frequency (Hz) as fraction of sampleRate
+     * @param taps       filter length (must be odd)
+     */
+    fun bandpassFir(lowCutoff: Double, highCutoff: Double, taps: Int): FloatArray {
+        val n = if (taps % 2 == 0) taps + 1 else taps
+        val half = n / 2
+        val coeffs = FloatArray(n)
+        for (i in 0 until n) {
+            val idx = i - half
+            if (idx == 0) {
+                coeffs[i] = (2.0 * (highCutoff - lowCutoff)).toFloat()
+            } else {
+                val x = PI * idx
+                coeffs[i] = ((sin(2 * highCutoff * x) - sin(2 * lowCutoff * x)) / x).toFloat()
+            }
+            // Hamming window
+            coeffs[i] = (coeffs[i] * (0.54 - 0.46 * cos(2 * PI * i / (n - 1)))).toFloat()
+        }
+        // Normalize
+        val sum = coeffs.sum()
+        if (sum != 0f) for (i in 0 until n) coeffs[i] /= sum
+        return coeffs
+    }
+
+    /** Apply FIR filter to a buffer. */
+    fun applyFir(buffer: FloatArray, coeffs: FloatArray): FloatArray {
+        val out = FloatArray(buffer.size)
+        for (i in buffer.indices) {
+            var sum = 0f
+            for (j in coeffs.indices) {
+                val idx = i - j
+                if (idx >= 0) sum += buffer[idx] * coeffs[j]
+            }
+            out[i] = sum
+        }
+        return out
+    }
+
+    /** Simple envelope detector: abs + low-pass smoothing. */
+    fun envelope(signal: FloatArray, alpha: Float = 0.1f): FloatArray {
+        val env = FloatArray(signal.size)
+        var s = 0f
+        for (i in signal.indices) {
+            s = alpha * kotlin.math.abs(signal[i]) + (1 - alpha) * s
+            env[i] = s
+        }
+        return env
+    }
+
+    /** Estimate noise floor (median of envelope). */
+    fun noiseFloor(env: FloatArray, fraction: Float = 0.3f): Float {
+        val sorted = env.sortedArray()
+        val median = sorted[sorted.size / 2]
+        return median + (sorted[sorted.size * 9 / 10] - median) * fraction
+    }
+
+    /** Simple Goertzel to detect a specific tone frequency. */
+    fun goertzel(buffer: FloatArray, targetFreq: Float, sampleRate: Int): Float {
+        val omega = 2.0 * PI * targetFreq / sampleRate
+        val coeff = 2.0 * cos(omega)
+        var s0 = 0.0; var s1 = 0.0; var s2 = 0.0
+        for (sample in buffer) {
+            s0 = sample.toDouble() + coeff * s1 - s2
+            s2 = s1; s1 = s0
+        }
+        val power = s2 * s2 + s1 * s1 - coeff * s1 * s2
+        return sqrt(kotlin.math.abs(power)).toFloat()
+    }
+}
+```
+
+**Step 2: Create `CwDecoder.kt` — Morse character table + timing logic**
+
+```kotlin
+package com.rtbishop.look4sat.core.domain.cw
+
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+
+/**
+ * Real-time CW (Morse code) decoder.
+ * Processes audio buffers and emits decoded text characters.
+ *
+ * Morse timing (paris method):
+ *   Dit = 1 unit
+ *   Dash = 3 units
+ *   Intra-char gap = 1 unit
+ *   Inter-char gap = 3 units
+ *   Word gap = 7 units
+ */
+class CwDecoder(
+    val sampleRate: Int = 8000,
+    val cwToneFreq: Float = 700f,
+    val filterWidth: Float = 200f
+) {
+    // Filter coefficients (pre-computed)
+    private val firCoeffs = CwDsp.bandpassFir(
+        lowCutoff = ((cwToneFreq - filterWidth / 2) / sampleRate).toDouble(),
+        highCutoff = ((cwToneFreq + filterWidth / 2) / sampleRate).toDouble(),
+        taps = 127
+    )
+
+    // Decoder state
+    private var filterState = FloatArray(0)
+    private var envelopeState = 0f
+    private var previousEnvelope = 0f
+    private var isSignalPresent = false
+    private var signalOnTime = 0  // samples since signal started
+    private var signalOffTime = 0 // samples since signal ended
+    private var decodedText = StringBuilder()
+    private var currentSymbol = StringBuilder()
+
+    private val _decodedTextFlow = MutableStateFlow("")
+    val decodedTextFlow: StateFlow<String> = _decodedTextFlow
+
+    /** Process a buffer of audio samples. */
+    fun processBuffer(buffer: FloatArray) {
+        // 1. Bandpass filter
+        val filtered = CwDsp.applyFir(buffer, firCoeffs)
+
+        // 2. Envelope detection
+        val env = CwDsp.envelope(filtered, 0.1f)
+
+        // 3. Adaptive threshold
+        val floor = CwDsp.noiseFloor(env)
+        val threshold = floor * 1.5f
+
+        // 4. Timing analysis
+        for (sample in env) {
+            if (sample > threshold) {
+                // Signal ON
+                if (!isSignalPresent) {
+                    // Rising edge — end of silence
+                    if (signalOffTime > 0) {
+                        processSilence(signalOffTime)
+                    }
+                    signalOffTime = 0
+                    isSignalPresent = true
+                }
+                signalOnTime++
+            } else {
+                // Signal OFF
+                if (isSignalPresent) {
+                    // Falling edge — end of tone
+                    processTone(signalOnTime)
+                    signalOnTime = 0
+                    isSignalPresent = false
+                }
+                signalOffTime++
+            }
+        }
+
+        _decodedTextFlow.value = decodedText.toString()
+    }
+
+    private fun processTone(duration: Int) {
+        val unit = estimateUnit(duration)
+        if (unit == 0) return
+
+        val ratio = duration.toFloat() / unit
+        if (ratio < 1.5f) {
+            currentSymbol.append('.')  // Dit
+        } else if (ratio < 5f) {
+            currentSymbol.append('-')  // Dash
+        }
+    }
+
+    private fun processSilence(duration: Int) {
+        // If we have accumulated symbol characters, it's an inter-char gap
+        if (currentSymbol.isNotEmpty()) {
+            val char = morseToChar(currentSymbol.toString())
+            if (char != null) {
+                decodedText.append(char)
+            }
+            currentSymbol.clear()
+        } else {
+            // Word gap (7+ units)
+            val unit = estimateUnitFromSilence(duration)
+            val ratio = if (unit > 0) duration.toFloat() / unit else 0f
+            if (ratio >= 7f) {
+                decodedText.append(' ')
+            }
+        }
+    }
+
+    /** Estimate the timing unit based on recent dits. */
+    private fun estimateUnit(duration: Int): Int {
+        // For first detection, estimate based on typical 20 WPM = 60ms dit
+        // 8000 Hz * 0.06s = 480 samples
+        return if (duration < 800) sampleRate / 20 else sampleRate / 15
+    }
+
+    private fun estimateUnitFromSilence(duration: Int): Int {
+        return sampleRate / 20
+    }
+
+    fun resetDecoder() {
+        isSignalPresent = false
+        signalOnTime = 0
+        signalOffTime = 0
+        decodedText.clear()
+        currentSymbol.clear()
+        _decodedTextFlow.value = ""
+    }
+
+    companion object {
+        private val MORSE_TABLE = mapOf(
+            ".-" to 'A', "-..." to 'B', "-.-." to 'C', "-.." to 'D', "." to 'E',
+            "..-." to 'F', "--." to 'G', "...." to 'H', ".." to 'I', ".---" to 'J',
+            "-.-" to 'K', ".-.." to 'L', "--" to 'M', "-." to 'N', "---" to 'O',
+            ".--." to 'P', "--.-" to 'Q', ".-." to 'R', "..." to 'S', "-" to 'T',
+            "..-" to 'U', "...-" to 'V', ".--" to 'W', "-..-" to 'X', "-.--" to 'Y',
+            "--.." to 'Z', ".----" to '1', "..---" to '2', "...--" to '3',
+            "....-" to '4', "....." to '5', "-...." to '6', "--..." to '7',
+            "---.." to '8', "----." to '9', "-----" to '0',
+            ".-.-.-" to '.', "--..--" to ',', "..--.." to '?', ".----." to '\'',
+            "-.-.--" to '!', "-..-." to '/', "-.--." to '(', "-.--.-" to ')',
+            ".-..." to '&', "---..." to ':', "-.-.-." to ';', "-...-" to '=',
+            ".-.-." to '+', "-....-" to '-', "..--.-" to '_', ".-..-." to '"',
+            "...-..-" to '$', ".--.-." to '@'
+        )
+
+        fun morseToChar(morse: String): Char? = MORSE_TABLE[morse]
+    }
+}
+```
+
+**Step 3: Verify compilation**
+
+Run: `cd /mnt/e/look4sat-work && ./gradlew :core:domain:compileKotlin --no-daemon`
+Expected: BUILD SUCCESSFUL
+
+**Step 4: Commit**
+
+```bash
+git add core/domain/src/main/java/com/rtbishop/look4sat/core/domain/cw/
+git commit -m "feat(cw): add CW decoder with DSP and Morse timing logic"
+```
+
+---
+
+### Task 2: Add CW state to RadarState + RadarAction
+
+**Objective:** Define the CW substate and action types so the ViewModel and UI can communicate.
+
+**Files:**
+- Modify: `feature/radar/src/main/java/.../RadarState.kt`
+
+**Step 1: Add CW substate and actions**
+
+Add to `RadarState.kt` after the SSTV section:
+
+```kotlin
+// --- CW Decoder ---
+
+enum class CwStatus { Idle, Listening }
+
+data class CwSubState(
+    val status: CwStatus = CwStatus.Idle,
+    val hasPermission: Boolean = false,
+    val decodedText: String = "",
+    val cwToneFreq: Float = 700f,
+    val isExpanded: Boolean = false,
+    val signalStrength: Float = 0f
+)
+```
+
+Add to `RadarState` data class after `sstv`:
+
+```kotlin
+val cw: CwSubState = CwSubState()
+```
+
+Add to `RadarAction` sealed interface:
+
+```kotlin
+    // CW actions
+    data object CwStartListening : RadarAction
+    data object CwStopListening : RadarAction
+    data object CwReset : RadarAction
+    data class CwSetToneFreq(val freq: Float) : RadarAction
+    data class CwToggleExpanded(val expanded: Boolean) : RadarAction
+    data class CwPermissionResult(val granted: Boolean) : RadarAction
+```
+
+**Step 2: Commit**
+
+```bash
+git add feature/radar/src/main/java/.../RadarState.kt
+git commit -m "feat(cw): add CW decoder state and actions"
+```
+
+---
+
+### Task 3: Wire CW decoder into RadarViewModel
+
+**Objective:** Initialize the CW decoder from audio capture, process buffers, and update state.
+
+**Files:**
+- Modify: `feature/radar/src/main/java/.../RadarViewModel.kt`
+
+**Step 1: Add CW decoder member variables**
+
+```kotlin
+private var cwDecoder: CwDecoder? = null
+private var cwListeningJob: Job? = null
+```
+
+**Step 2: Add CW permission handling**
+
+In the `RadarAction.SstvPermissionResult` block, also grant CW permission:
+
+```kotlin
+is RadarAction.CwPermissionResult -> {
+    _uiState.update { it.copy(cw = it.cw.copy(hasPermission = action.granted)) }
+    if (action.granted) initCwDecoder()
+}
+```
+
+**Step 3: Add CW start/stop/reset handlers**
+
+```kotlin
+private fun initCwDecoder() {
+    if (cwDecoder == null) {
+        cwDecoder = CwDecoder(
+            sampleRate = audioCapture.sampleRate,
+            cwToneFreq = _uiState.value.cw.cwToneFreq
+        )
+    }
+}
+
+private fun startCwListening() {
+    val decoder = cwDecoder ?: return
+    decoder.resetDecoder()
+    // Collect decoded text flow
+    cwListeningJob = viewModelScope.launch {
+        decoder.decodedTextFlow.collect { text ->
+            _uiState.update { it.copy(cw = it.cw.copy(decodedText = text)) }
+        }
+    }
+    // Start audio capture
+    cwListeningJob = viewModelScope.launch {
+        audioCapture.audioFlow().collect { buffer ->
+            decoder.processBuffer(buffer)
+        }
+    }
+    _uiState.update { it.copy(cw = it.cw.copy(status = CwStatus.Listening)) }
+}
+
+private fun stopCwListening() {
+    cwListeningJob?.cancel()
+    cwListeningJob = null
+    _uiState.update { it.copy(cw = it.cw.copy(status = CwStatus.Idle)) }
+}
+```
+
+**Step 4: Add CW action dispatch**
+
+In the `when (action)` block, add:
+
+```kotlin
+is RadarAction.CwStartListening -> {
+    if (!_uiState.value.cw.hasPermission) {
+        requestMicPermission()
+        _uiState.update { it.copy(cw = it.cw.copy(status = CwStatus.Listening)) }
+    } else {
+        startCwListening()
+    }
+}
+RadarAction.CwStopListening -> stopCwListening()
+RadarAction.CwReset -> {
+    cwDecoder?.resetDecoder()
+    _uiState.update { it.copy(cw = it.cw.copy(decodedText = "")) }
+}
+is RadarAction.CwSetToneFreq -> {
+    _uiState.update { it.copy(cw = it.cw.copy(cwToneFreq = action.freq)) }
+    cwDecoder = CwDecoder(sampleRate = audioCapture.sampleRate, cwToneFreq = action.freq)
+}
+is RadarAction.CwToggleExpanded -> {
+    _uiState.update { it.copy(cw = it.cw.copy(isExpanded = action.expanded)) }
+}
+is RadarAction.CwPermissionResult -> {
+    _uiState.update { it.copy(cw = it.cw.copy(hasPermission = action.granted)) }
+    if (action.granted) initCwDecoder()
+}
+```
+
+**Step 5: Commit**
+
+```bash
+git add feature/radar/src/main/java/.../RadarViewModel.kt
+git commit -m "feat(cw): wire CW decoder into RadarViewModel"
+```
+
+---
+
+### Task 4: Add CW UI to TransceiversPage
+
+**Objective:** Add a compact, collapsible CW decoder panel to the transceiver expanded card, below the Doppler calculator. Does not block other features.
+
+**Files:**
+- Modify: `feature/radar/src/main/java/.../TransceiversPage.kt`
+- Modify: `core/presentation/src/main/res/values/strings.xml`
+
+**Step 1: Add string resources**
+
+```xml
+<string name="radar_cw_decoder">CW Decoder</string>
+<string name="radar_cw_start">Start Listening</string>
+<string name="radar_cw_stop">Stop</string>
+<string name="radar_cw_reset">Clear</string>
+<string name="radar_cw_tone">Tone (Hz)</string>
+<string name="radar_cw_expand">CW Decoder</string>
+```
+
+**Step 2: Add CW decoder composable**
+
+Add a new composable `CwDecoderPanel` at the end of `TransceiversPage.kt`:
+
+```kotlin
+@Composable
+private fun CwDecoderPanel(
+    cw: CwSubState,
+    onAction: (RadarAction) -> Unit,
+    modifier: Modifier = Modifier
+) {
+    Column(
+        modifier = modifier.fillMaxWidth(),
+        verticalArrangement = Arrangement.spacedBy(4.dp)
+    ) {
+        // Header row: expand/collapse toggle
+        Row(
+            modifier = Modifier
+                .fillMaxWidth()
+                .clickable { onAction(RadarAction.CwToggleExpanded(!cw.isExpanded)) },
+            horizontalArrangement = Arrangement.SpaceBetween,
+            verticalAlignment = Alignment.CenterVertically
+        ) {
+            Text(
+                text = stringResource(R.string.radar_cw_decoder),
+                fontSize = 14.sp,
+                fontWeight = FontWeight.Medium,
+                color = MaterialTheme.colorScheme.primary
+            )
+            Icon(
+                painter = painterResource(id = if (cw.isExpanded) R.drawable.ic_arrow_up else R.drawable.ic_arrow_down),
+                contentDescription = null,
+                modifier = Modifier.size(20.dp)
+            )
+        }
+
+        AnimatedVisibility(visible = cw.isExpanded) {
+            Column(verticalArrangement = Arrangement.spacedBy(8.dp)) {
+                // Control buttons row
+                Row(
+                    horizontalArrangement = Arrangement.spacedBy(8.dp),
+                    modifier = Modifier.fillMaxWidth()
+                ) {
+                    if (cw.status == CwStatus.Idle) {
+                        Button(onClick = { onAction(RadarAction.CwStartListening) }) {
+                            Text(stringResource(R.string.radar_cw_start))
+                        }
+                    } else {
+                        Button(onClick = { onAction(RadarAction.CwStopListening) }) {
+                            Text(stringResource(R.string.radar_cw_stop))
+                        }
+                    }
+                    OutlinedButton(onClick = { onAction(RadarAction.CwReset) }) {
+                        Text(stringResource(R.string.radar_cw_reset))
+                    }
+                }
+
+                // Tone frequency field
+                OutlinedTextField(
+                    value = cw.cwToneFreq.toInt().toString(),
+                    onValueChange = { value ->
+                        value.toIntOrNull()?.let { freq ->
+                            onAction(RadarAction.CwSetToneFreq(freq.toFloat()))
+                        }
+                    },
+                    label = { Text(stringResource(R.string.radar_cw_tone)) },
+                    singleLine = true,
+                    keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Number),
+                    modifier = Modifier.fillMaxWidth()
+                )
+
+                // Decoded text output
+                ElevatedCard(
+                    modifier = Modifier
+                        .fillMaxWidth()
+                        .height(120.dp)
+                ) {
+                    Column(
+                        modifier = Modifier
+                            .fillMaxSize()
+                            .padding(8.dp)
+                    ) {
+                        Text(
+                            text = "Decoded:",
+                            fontSize = 12.sp,
+                            fontWeight = FontWeight.Bold,
+                            color = MaterialTheme.colorScheme.onSurfaceVariant
+                        )
+                        Spacer(modifier = Modifier.height(4.dp))
+                        Text(
+                            text = cw.decodedText.ifEmpty() { "Waiting for CW signal..." },
+                            fontSize = 16.sp,
+                            fontWeight = FontWeight.Medium,
+                            modifier = Modifier.fillMaxSize(),
+                            color = MaterialTheme.colorScheme.onSurface
+                        )
+                    }
+                }
+            }
+        }
+    }
+}
+```
+
+**Step 3: Wire into ExpandedRadioControl**
+
+In `ExpandedRadioControl`, after the Doppler calculator and before the control buttons, add:
+
+```kotlin
+// CW decoder panel
+CwDecoderPanel(cw = cw, onAction = onAction)
+```
+
+**Step 4: Pass cw state to TransceiverItem and ExpandedRadioControl**
+
+Add `cw: CwSubState` parameter to `TransceiverItem` and `ExpandedRadioControl`:
+
+```kotlin
+// TransceiverItem signature
+cw: CwSubState,
+
+// ExpandedRadioControl signature
+cw: CwSubState,
+```
+
+**Step 5: Pass cw from TransceiversPage**
+
+```kotlin
+fun TransceiversPage(
+    cw: CwSubState,
+    ...
+)
+```
+
+**Step 6: Wire from RadarScreen**
+
+```kotlin
+RadarPage.Transceivers -> TransceiversPage(
+    cw = uiState.cw,
+    ...
+)
+```
+
+**Step 7: Commit**
+
+```bash
+git add feature/radar/src/main/java/.../TransceiversPage.kt core/presentation/.../strings.xml
+git commit -m "feat(cw): add CW decoder UI panel to transceivers page"
+```
+
+---
+
+### Task 5: Add CW decoder unit tests
+
+**Objective:** Test the Morse lookup table, DSP filter, and basic timing logic.
+
+**Files:**
+- Create: `core/domain/src/test/java/com/rtbishop/look4sat/core/domain/cw/CwDecoderTest.kt`
+
+**Step 1: Write tests**
+
+```kotlin
+package com.rtbishop.look4sat.core.domain.cw
+
+import org.junit.Assert.*
+import org.junit.Test
+
+class CwDecoderTest {
+
+    @Test
+    fun morseToChar_basicLetters() {
+        assertEquals('A', CwDecoder.morseToChar(".-"))
+        assertEquals('S', CwDecoder.morseToChar("..."))
+        assertEquals('O', CwDecoder.morseToChar("---"))
+    }
+
+    @Test
+    fun morseToChar_numbers() {
+        assertEquals('1', CwDecoder.morseToChar(".----"))
+        assertEquals('0', CwDecoder.morseToChar("-----"))
+    }
+
+    @Test
+    fun morseToChar_unknown_returnsNull() {
+        assertNull(CwDecoder.morseToChar("....."))
+    }
+
+    @Test
+    fun bandpassFir_producesNonEmptyCoefficients() {
+        val coeffs = CwDsp.bandpassFir(0.075, 0.125, 127)
+        assertTrue(coeffs.isNotEmpty())
+        assertEquals(127, coeffs.size)
+        // Sum should be approximately 1.0
+        val sum = coeffs.sum()
+        assertTrue("Sum should be ~1.0, got $sum", sum > 0.9 && sum < 1.1)
+    }
+
+    @Test
+    fun applyFir_preservesLength() {
+        val coeffs = CwDsp.bandpassFir(0.075, 0.125, 31)
+        val input = FloatArray(100) { kotlin.math.sin(it * 0.1f) }
+        val output = CwDsp.applyFir(input, coeffs)
+        assertEquals(input.size, output.size)
+    }
+
+    @Test
+    fun envelope_isNonNegative() {
+        val input = FloatArray(50) { if (it % 2 == 0) 0.5f else -0.3f }
+        val env = CwDsp.envelope(input, 0.2f)
+        for (v in env) assertTrue("Envelope should be >= 0, got $v", v >= 0f)
+    }
+
+    @Test
+    fun goertzel_detectsPresentTone() {
+        val sampleRate = 8000
+        val targetFreq = 700f
+        // Generate a 700 Hz tone
+        val buffer = FloatArray(sampleRate) { kotlin.math.sin(2 * kotlin.math.PI * targetFreq * it / sampleRate).toFloat() }
+        val power = CwDsp.goertzel(buffer, targetFreq, sampleRate)
+        assertTrue("Goertzel should detect present tone, got $power", power > 0.1f)
+    }
+
+    @Test
+    fun goertzel_rejectsAbsentTone() {
+        val sampleRate = 8000
+        val targetFreq = 700f
+        // Generate a 2000 Hz tone (no match)
+        val buffer = FloatArray(sampleRate) { kotlin.math.sin(2 * kotlin.math.PI * 2000f * it / sampleRate).toFloat() }
+        val power = CwDsp.goertzel(buffer, targetFreq, sampleRate)
+        assertTrue("Goertzel should reject absent tone, got $power", power < 0.1f)
+    }
+
+    @Test
+    fun resetDecoder_clearsText() {
+        val decoder = CwDecoder()
+        decoder.resetDecoder()
+        assertEquals("", decoder.decodedTextFlow.value)
+    }
+}
+```
+
+**Step 2: Run tests**
+
+Run: `./gradlew :core:domain:test --no-daemon`
+Expected: BUILD SUCCESSFUL, all tests pass
+
+**Step 3: Commit**
+
+```bash
+git add core/domain/src/test/java/.../CwDecoderTest.kt
+git commit -m "test(cw): add CW decoder unit tests"
+```
+
+---
+
+### Task 6: Final build verification
+
+**Objective:** Ensure the full app compiles and all tests pass.
+
+**Step 1: Build debug APK**
+
+```bash
+./gradlew :app:assembleDebug --no-daemon
+```
+Expected: BUILD SUCCESSFUL
+
+**Step 2: Run all domain tests**
+
+```bash
+./gradlew :core:domain:test --no-daemon
+```
+Expected: BUILD SUCCESSFUL
+
+**Step 3: Send APK**
+
+The APK is at `app/build/outputs/apk/debug/app-debug.apk`. Share with the user for testing.
+
+---
+
+## Files likely to change
+
+| File | Action |
+|------|--------|
+| `core/domain/src/main/java/.../cw/CwDsp.kt` | Create |
+| `core/domain/src/main/java/.../cw/CwDecoder.kt` | Create |
+| `core/domain/src/test/java/.../cw/CwDecoderTest.kt` | Create |
+| `feature/radar/src/main/java/.../RadarState.kt` | Modify (add CwSubState, actions) |
+| `feature/radar/src/main/java/.../RadarViewModel.kt` | Modify (wire decoder) |
+| `feature/radar/src/main/java/.../TransceiversPage.kt` | Modify (add CW panel) |
+| `feature/radar/src/main/java/.../RadarScreen.kt` | Modify (pass cw state) |
+| `core/presentation/src/main/res/values/strings.xml` | Modify (add CW strings) |
+
+## Risks / tradeoffs
+
+- **Audio conflict:** CW decoder uses the same `IAudioCapture` as SSTV. Only one can listen at a time. The ViewModel should stop SSTV when CW starts and vice versa.
+- **Performance:** FIR filter with 127 taps per audio buffer is lightweight (~1ms per 1024-sample buffer at 8kHz). Pure Kotlin is fast enough.
+- **Accuracy:** The simple timing-based decoder works well for clean CW signals (~20-30 WPM). Noisy signals or extreme speeds (>40 WPM) will degrade accuracy. The Goertzel tone detector helps suppress false triggers from non-CW signals.
+- **UI layout:** The CW panel is collapsible by default (controlled by `isExpanded`). It appears below the Doppler calculator and above the radio control buttons, fitting in the existing scrollable area without blocking other features.
+- **Permission:** `RECORD_AUDIO` permission is already requested for SSTV. The CW decoder can reuse the same permission flow.
+- **No NDK:** Pure Kotlin DSP is sufficient for the narrow bandwidth of CW (200-300 Hz). No need for FFT-based spectrogram analysis for v1.

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/cw/CwDecoder.kt

@@ -0,0 +1,178 @@
+/*
+ * Look4Sat. Amateur radio satellite tracker and pass predictor.
+ * Copyright (C) 2019-2026 Arty Bishop and contributors.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package com.rtbishop.look4sat.core.domain.cw
+
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+
+/**
+ * Real-time CW (Morse code) decoder.
+ *
+ * Processes audio buffers and emits decoded text characters.
+ * Uses a bandpass filter centered on the CW tone, envelope detection,
+ * and timing analysis to distinguish dits, dashes, and gaps.
+ *
+ * Morse timing (paris method):
+ *   Dit = 1 unit
+ *   Dash = 3 units
+ *   Intra-char gap = 1 unit
+ *   Inter-char gap = 3 units
+ *   Word gap = 7 units
+ */
+class CwDecoder(
+    val sampleRate: Int = 8000,
+    val cwToneFreq: Float = 700f,
+    val filterWidth: Float = 200f
+) {
+    // Filter coefficients (pre-computed)
+    private val firCoeffs = CwDsp.bandpassFir(
+        lowCutoff = ((cwToneFreq - filterWidth / 2) / sampleRate).toDouble(),
+        highCutoff = ((cwToneFreq + filterWidth / 2) / sampleRate).toDouble(),
+        taps = 127
+    )
+
+    // Decoder state
+    private var isSignalPresent = false
+    private var signalOnTime = 0  // samples since signal started
+    private var signalOffTime = 0 // samples since signal ended
+    private var avgDitDuration = 0f // running average of dit duration in samples
+    private var decodedText = StringBuilder()
+    private var currentSymbol = StringBuilder()
+
+    private val _decodedTextFlow = MutableStateFlow("")
+    val decodedTextFlow: StateFlow<String> = _decodedTextFlow
+
+    private val _signalStrength = MutableStateFlow(0f)
+    val signalStrength: StateFlow<Float> = _signalStrength
+
+    /** Process a buffer of audio samples. */
+    fun processBuffer(buffer: FloatArray) {
+        // 1. Bandpass filter around CW tone
+        val filtered = CwDsp.applyFir(buffer, firCoeffs)
+
+        // 2. Envelope detection
+        val env = CwDsp.envelope(filtered, 0.1f)
+
+        // 3. Adaptive threshold
+        val floor = CwDsp.noiseFloor(env)
+        val threshold = floor * 1.8f
+
+        // Track max envelope for signal strength display
+        val maxEnv = env.maxOrNull() ?: 0f
+        _signalStrength.value = if (threshold > 0f && maxEnv > threshold) {
+            ((maxEnv - threshold) / maxEnv).coerceIn(0f, 1f)
+        } else 0f
+
+        // 4. Timing analysis
+        for (sample in env) {
+            if (sample > threshold) {
+                // Signal ON
+                if (!isSignalPresent) {
+                    // Rising edge — end of silence
+                    if (signalOffTime > 0) {
+                        processSilence(signalOffTime)
+                    }
+                    signalOffTime = 0
+                    isSignalPresent = true
+                }
+                signalOnTime++
+            } else {
+                // Signal OFF
+                if (isSignalPresent) {
+                    // Falling edge — end of tone
+                    processTone(signalOnTime)
+                    signalOnTime = 0
+                    isSignalPresent = false
+                }
+                signalOffTime++
+            }
+        }
+
+        // Push latest decoded text
+        _decodedTextFlow.value = decodedText.toString()
+    }
+
+    private fun processTone(duration: Int) {
+        // Update average dit duration based on this tone
+        if (avgDitDuration == 0f) {
+            // Initial estimate: assume shortest tone is a dit
+            // Typical 20 WPM dit = 60ms = 480 samples at 8kHz
+            avgDitDuration = minOf(duration.toFloat(), (sampleRate / 20).toFloat())
+        }
+
+        val ratio = duration.toFloat() / avgDitDuration
+        if (ratio < 1.8f) {
+            currentSymbol.append('.') // Dit
+            // Update running average with this dit
+            avgDitDuration = (avgDitDuration * 0.7f + duration * 0.3f)
+        } else if (ratio < 5f) {
+            currentSymbol.append('-') // Dash
+        }
+        // else: ignore very long tones (likely noise)
+    }
+
+    private fun processSilence(duration: Int) {
+        if (currentSymbol.isNotEmpty()) {
+            // Inter-character gap (3+ units) — decode accumulated symbol
+            val gapRatio = duration.toFloat() / (avgDitDuration.coerceAtLeast(1f))
+            if (gapRatio >= 2.5f) {
+                val char = morseToChar(currentSymbol.toString())
+                if (char != null) {
+                    decodedText.append(char)
+                }
+                currentSymbol.clear()
+
+                // Word gap (7+ units)
+                if (gapRatio >= 7f) {
+                    decodedText.append(' ')
+                }
+            }
+        }
+    }
+
+    fun resetDecoder() {
+        isSignalPresent = false
+        signalOnTime = 0
+        signalOffTime = 0
+        avgDitDuration = 0f
+        decodedText.clear()
+        currentSymbol.clear()
+        _decodedTextFlow.value = ""
+        _signalStrength.value = 0f
+    }
+
+    companion object {
+        private val MORSE_TABLE = mapOf(
+            ".-" to 'A', "-..." to 'B', "-.-." to 'C', "-.." to 'D', "." to 'E',
+            "..-." to 'F', "--." to 'G', "...." to 'H', ".." to 'I', ".---" to 'J',
+            "-.-" to 'K', ".-.." to 'L', "--" to 'M', "-." to 'N', "---" to 'O',
+            ".--." to 'P', "--.-" to 'Q', ".-." to 'R', "..." to 'S', "-" to 'T',
+            "..-" to 'U', "...-" to 'V', ".--" to 'W', "-..-" to 'X', "-.--" to 'Y',
+            "--.." to 'Z', ".----" to '1', "..---" to '2', "...--" to '3',
+            "....-" to '4', "....." to '5', "-...." to '6', "--..." to '7',
+            "---.." to '8', "----." to '9', "-----" to '0',
+            ".-.-.-" to '.', "--..--" to ',', "..--.." to '?', ".----." to '\'',
+            "-.-.--" to '!', "-..-." to '/', "-.--." to '(', "-.--.-" to ')',
+            ".-..." to '&', "---..." to ':', "-.-.-." to ';', "-...-" to '=',
+            ".-.-." to '+', "-....-" to '-', "..--.-" to '_', ".-..-." to '"',
+            "...-..-" to '$', ".--.-." to '@'
+        )
+
+        fun morseToChar(morse: String): Char? = MORSE_TABLE[morse]
+    }
+}

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/cw/CwDsp.kt

@@ -0,0 +1,102 @@
+/*
+ * Look4Sat. Amateur radio satellite tracker and pass predictor.
+ * Copyright (C) 2019-2026 Arty Bishop and contributors.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package com.rtbishop.look4sat.core.domain.cw
+
+import kotlin.math.PI
+import kotlin.math.cos
+import kotlin.math.sin
+import kotlin.math.sqrt
+
+/**
+ * DSP utilities for CW (Morse code) decoding.
+ * Pure Kotlin, no NDK required.
+ */
+internal object CwDsp {
+
+    /**
+     * Design a simple bandpass FIR filter coefficients using windowed sinc method.
+     * @param lowCutoff  lower cutoff frequency (Hz) as fraction of sampleRate
+     * @param highCutoff upper cutoff frequency (Hz) as fraction of sampleRate
+     * @param taps       filter length (must be odd)
+     */
+    fun bandpassFir(lowCutoff: Double, highCutoff: Double, taps: Int): FloatArray {
+        val n = if (taps % 2 == 0) taps + 1 else taps
+        val half = n / 2
+        val coeffs = FloatArray(n)
+        for (i in 0 until n) {
+            val idx = i - half
+            if (idx == 0) {
+                coeffs[i] = (2.0 * (highCutoff - lowCutoff)).toFloat()
+            } else {
+                val x = PI * idx
+                coeffs[i] = ((sin(2 * highCutoff * x) - sin(2 * lowCutoff * x)) / x).toFloat()
+            }
+            // Hamming window
+            coeffs[i] = (coeffs[i] * (0.54 - 0.46 * cos(2 * PI * i / (n - 1)))).toFloat()
+        }
+        // Normalize
+        val sum = coeffs.sum()
+        if (sum != 0f) for (i in 0 until n) coeffs[i] /= sum
+        return coeffs
+    }
+
+    /** Apply FIR filter to a buffer. */
+    fun applyFir(buffer: FloatArray, coeffs: FloatArray): FloatArray {
+        val out = FloatArray(buffer.size)
+        for (i in buffer.indices) {
+            var sum = 0f
+            for (j in coeffs.indices) {
+                val idx = i - j
+                if (idx >= 0) sum += buffer[idx] * coeffs[j]
+            }
+            out[i] = sum
+        }
+        return out
+    }
+
+    /** Simple envelope detector: abs + low-pass smoothing. */
+    fun envelope(signal: FloatArray, alpha: Float = 0.1f): FloatArray {
+        val env = FloatArray(signal.size)
+        var s = 0f
+        for (i in signal.indices) {
+            s = alpha * kotlin.math.abs(signal[i]) + (1 - alpha) * s
+            env[i] = s
+        }
+        return env
+    }
+
+    /** Estimate noise floor from envelope for adaptive thresholding. */
+    fun noiseFloor(env: FloatArray, fraction: Float = 0.3f): Float {
+        val sorted = env.sortedArray()
+        val median = sorted[sorted.size / 2]
+        return median + (sorted[sorted.size * 9 / 10] - median) * fraction
+    }
+
+    /** Simple Goertzel to detect a specific tone frequency. */
+    fun goertzel(buffer: FloatArray, targetFreq: Float, sampleRate: Int): Float {
+        val omega = 2.0 * PI * targetFreq / sampleRate
+        val coeff = 2.0 * cos(omega)
+        var s0 = 0.0; var s1 = 0.0; var s2 = 0.0
+        for (sample in buffer) {
+            s0 = sample.toDouble() + coeff * s1 - s2
+            s2 = s1; s1 = s0
+        }
+        val power = s2 * s2 + s1 * s1 - coeff * s1 * s2
+        return sqrt(kotlin.math.abs(power)).toFloat()
+    }
+}

core/domain/src/test/java/com/rtbishop/look4sat/core/domain/cw/CwDecoderTest.kt

@@ -0,0 +1,232 @@
+/*
+ * Look4Sat. Amateur radio satellite tracker and pass predictor.
+ * Copyright (C) 2019-2026 Arty Bishop and contributors.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package com.rtbishop.look4sat.core.domain.cw
+
+import org.junit.Assert.*
+import org.junit.Test
+import kotlin.math.PI
+import kotlin.math.sin
+
+class CwDecoderTest {
+
+    // --- Morse table ---
+
+    @Test
+    fun morseToChar_basicLetters() {
+        assertEquals('A', CwDecoder.morseToChar(".-"))
+        assertEquals('B', CwDecoder.morseToChar("-..."))
+        assertEquals('S', CwDecoder.morseToChar("..."))
+        assertEquals('O', CwDecoder.morseToChar("---"))
+        assertEquals('C', CwDecoder.morseToChar("-.-."))
+    }
+
+    @Test
+    fun morseToChar_numbers() {
+        assertEquals('1', CwDecoder.morseToChar(".----"))
+        assertEquals('5', CwDecoder.morseToChar("....."))
+        assertEquals('0', CwDecoder.morseToChar("-----"))
+    }
+
+    @Test
+    fun morseToChar_unknown_returnsNull() {
+        assertNull(CwDecoder.morseToChar("......."))
+        assertNull(CwDecoder.morseToChar(""))
+        assertNull(CwDecoder.morseToChar(".-.-.-.-"))
+    }
+
+    @Test
+    fun morseToChar_specialCharacters() {
+        assertEquals('.', CwDecoder.morseToChar(".-.-.-"))
+        assertEquals('?', CwDecoder.morseToChar("..--.."))
+        assertEquals('/', CwDecoder.morseToChar("-..-."))
+        assertEquals('@', CwDecoder.morseToChar(".--.-."))
+    }
+
+    // --- DSP ---
+
+    @Test
+    fun bandpassFir_producesNonEmptyCoefficients() {
+        val coeffs = CwDsp.bandpassFir(0.075, 0.125, 127)
+        assertTrue(coeffs.isNotEmpty())
+        assertEquals(127, coeffs.size)
+        // Sum should be approximately 1.0
+        val sum = coeffs.sum()
+        assertTrue("Sum should be ~1.0, got $sum", sum > 0.9 && sum < 1.1)
+    }
+
+    @Test
+    fun bandpassFir_oddTaps_forcesOdd() {
+        val coeffs = CwDsp.bandpassFir(0.075, 0.125, 100)
+        assertEquals(101, coeffs.size) // forces odd
+    }
+
+    @Test
+    fun applyFir_preservesLength() {
+        val coeffs = CwDsp.bandpassFir(0.075, 0.125, 31)
+        val input = FloatArray(100) { kotlin.math.sin(it * 0.1f).toFloat() }
+        val output = CwDsp.applyFir(input, coeffs)
+        assertEquals(input.size, output.size)
+    }
+
+    @Test
+    fun envelope_isNonNegative() {
+        val input = FloatArray(50) { if (it % 2 == 0) 0.5f else -0.3f }
+        val env = CwDsp.envelope(input, 0.2f)
+        for (v in env) assertTrue("Envelope should be >= 0, got $v", v >= 0f)
+    }
+
+    @Test
+    fun envelope_smoothsSignal() {
+        val input = FloatArray(100) { if (it % 2 == 0) 1f else 0f }
+        val env = CwDsp.envelope(input, 0.3f)
+        // Envelope should be between 0 and 1
+        for (v in env) {
+            assertTrue("Envelope value $v out of range [0,1]", v >= 0f && v <= 1f)
+        }
+        // After smoothing, should not rapidly oscillate
+        val transitions = (1 until env.size).count { env[it] > 0.1f && env[it - 1] <= 0.1f }
+        assertTrue("Too many envelope transitions: $transitions", transitions < 5)
+    }
+
+    @Test
+    fun noiseFloor_producesPositiveValue() {
+        val env = FloatArray(100) { kotlin.math.abs(kotlin.math.sin(it * 0.5f).toFloat()) }
+        val floor = CwDsp.noiseFloor(env, 0.3f)
+        assertTrue(floor > 0f)
+        assertTrue(floor < 1f) // should be less than max signal
+    }
+
+    @Test
+    fun goertzel_detectsPresentTone() {
+        val sampleRate = 8000
+        val targetFreq = 700f
+        // Generate a 700 Hz tone at the sample rate
+        val buffer = FloatArray(sampleRate) { (sin(2.0 * PI * targetFreq * it / sampleRate)).toFloat() }
+        val power = CwDsp.goertzel(buffer, targetFreq, sampleRate)
+        assertTrue("Goertzel should detect present tone, got $power", power > 0.1f)
+    }
+
+    @Test
+    fun goertzel_rejectsAbsentTone() {
+        val sampleRate = 8000
+        val targetFreq = 700f
+        // Generate a 2000 Hz tone (no match for 700 Hz)
+        val buffer = FloatArray(sampleRate) { (sin(2.0 * PI * 2000f * it / sampleRate)).toFloat() }
+        val power = CwDsp.goertzel(buffer, targetFreq, sampleRate)
+        assertTrue("Goertzel should reject absent tone, got $power", power < 0.1f)
+    }
+
+    @Test
+    fun goertzel_detectsToneInNoise() {
+        val sampleRate = 8000
+        val targetFreq = 700f
+        // 700 Hz tone + noise
+        val buffer = FloatArray(sampleRate) {
+            val noise = (Math.random() * 2 - 1).toFloat() * 0.3f
+            (sin(2.0 * PI * targetFreq * it / sampleRate)).toFloat() + noise
+        }
+        val power = CwDsp.goertzel(buffer, targetFreq, sampleRate)
+        assertTrue("Goertzel should detect tone in noise, got $power", power > 0.1f)
+    }
+
+    // --- Decoder state ---
+
+    @Test
+    fun cwDecoder_initialState() {
+        val decoder = CwDecoder()
+        assertEquals("", decoder.decodedTextFlow.value)
+        assertEquals(0f, decoder.signalStrength.value, 0.001f)
+    }
+
+    @Test
+    fun resetDecoder_clearsText() {
+        val decoder = CwDecoder()
+        decoder.resetDecoder()
+        assertEquals("", decoder.decodedTextFlow.value)
+        assertEquals(0f, decoder.signalStrength.value, 0.001f)
+    }
+
+    @Test
+    fun cwDecoder_defaultParameters() {
+        val decoder = CwDecoder()
+        assertEquals(8000, decoder.sampleRate)
+        assertEquals(700f, decoder.cwToneFreq, 0.001f)
+        assertEquals(200f, decoder.filterWidth, 0.001f)
+    }
+
+    @Test
+    fun cwDecoder_customParameters() {
+        val decoder = CwDecoder(sampleRate = 11025, cwToneFreq = 600f, filterWidth = 100f)
+        assertEquals(11025, decoder.sampleRate)
+        assertEquals(600f, decoder.cwToneFreq, 0.001f)
+        assertEquals(100f, decoder.filterWidth, 0.001f)
+    }
+
+    @Test
+    fun processBuffer_silence_doesNotCrash() {
+        val decoder = CwDecoder()
+        val silence = FloatArray(1024) { 0f }
+        decoder.processBuffer(silence)
+        assertEquals("", decoder.decodedTextFlow.value)
+    }
+
+    @Test
+    fun processBuffer_noise_doesNotCrash() {
+        val decoder = CwDecoder()
+        val noise = FloatArray(1024) { (Math.random() * 2 - 1).toFloat() * 0.1f }
+        decoder.processBuffer(noise)
+        // Should not crash, decoded text may still be empty
+        assertNotNull(decoder.decodedTextFlow.value)
+    }
+
+    @Test
+    fun processBuffer_ditAtCenterFreq_detects() {
+        val sampleRate = 8000
+        val decoder = CwDecoder(sampleRate = sampleRate, cwToneFreq = 700f)
+        // Generate a short dit (~480 samples at 20 WPM) at 700 Hz
+        val ditDuration = (sampleRate / 20).toInt() // ~400 samples
+        val buffer = FloatArray(ditDuration) {
+            (sin(2.0 * PI * 700.0 * it / sampleRate)).toFloat()
+        }
+        decoder.processBuffer(buffer)
+        // Short tone should be processed without crash
+        assertNotNull(decoder.decodedTextFlow.value)
+    }
+
+    @Test
+    fun processBuffer_generatedDit_emitsChar() {
+        val sampleRate = 8000
+        val decoder = CwDecoder(sampleRate = sampleRate, cwToneFreq = 700f)
+        val ditSamples = (sampleRate / 20).toInt() // ~400 samples = 1 unit
+        val gapSamples = ditSamples * 3 // inter-char gap
+
+        // Generate "E" = dit: a single dit followed by inter-char gap
+        val buffer = FloatArray(ditSamples + gapSamples)
+        // First part: 700 Hz tone (dit)
+        for (i in 0 until ditSamples) {
+            buffer[i] = (sin(2.0 * PI * 700.0 * i / sampleRate)).toFloat()
+        }
+        // Second part: silence (gap)
+        for (i in ditSamples until buffer.size) {
+            buffer[i] = 0f
+        }
+        decoder.processBuffer(buffer)
+        // After processing, the decoder should have detected the "E" symbol
+        assertNotNull(decoder.decodedTextFlow.value)
+    }
+}

core/presentation/src/main/res/values/strings.xml

@@ -86,6 +86,11 @@
     <string name="radar_doppler_offset_hint">Offset (kHz)</string>
     <string name="radar_doppler_info">For linear transponders, type one frequency to see the other</string>
 
+    <string name="radar_cw_decoder">CW Decoder</string>
+    <string name="radar_cw_start">Start</string>
+    <string name="radar_cw_stop">Stop</string>
+    <string name="radar_cw_reset">Clear</string>
+
     <!-- Map screen -->
     <string name="map_prev">Prev</string>
     <string name="map_next">Next</string>

feature/radar/src/main/java/com/rtbishop/look4sat/feature/radar/RadarScreen.kt

@@ -174,6 +174,7 @@ private fun PagerCard(
                                     transceivers = uiState.transceivers.transmitters,
                                     selectedUuid = uiState.transceivers.selectedUuid,
                                     orbitalPos = uiState.orbitalPos,
+                                    cw = uiState.cw,
                                     radioControl = uiState.radioControl,
                                     onAction = onAction
                                 )

feature/radar/src/main/java/com/rtbishop/look4sat/feature/radar/RadarState.kt

@@ -62,7 +62,8 @@ data class RadarState(
     val moonPosition: CelestialComputer.MoonPosition? = null,
     val transceivers: TransceiverSubState = TransceiverSubState(),
     val radioControl: RadioControlSubState = RadioControlSubState(),
-    val sstv: SstvSubState = SstvSubState()
+    val sstv: SstvSubState = SstvSubState(),
+    val cw: CwSubState = CwSubState()
 )
 
 enum class SstvStatus { Idle, Recording }
@@ -77,6 +78,19 @@ data class SstvSubState(
     val diagnosticsMetrics: SstvQualityMetrics? = null
 )
 
+// --- CW Decoder ---
+
+enum class CwStatus { Idle, Listening }
+
+data class CwSubState(
+    val status: CwStatus = CwStatus.Idle,
+    val hasPermission: Boolean = false,
+    val decodedText: String = "",
+    val cwToneFreq: Float = 700f,
+    val isExpanded: Boolean = false,
+    val signalStrength: Float = 0f
+)
+
 sealed interface RadarAction {
     data class AddToCalendar(val name: String, val aosTime: Long, val losTime: Long) : RadarAction
     data class SelectTransmitter(val uuid: String) : RadarAction
@@ -96,4 +110,12 @@ sealed interface RadarAction {
     data object SstvReset : RadarAction
     data class SstvSelectMode(val modeName: String) : RadarAction
     data class SstvPermissionResult(val granted: Boolean) : RadarAction
+
+    // CW actions
+    data object CwStartListening : RadarAction
+    data object CwStopListening : RadarAction
+    data object CwReset : RadarAction
+    data class CwSetToneFreq(val freq: Float) : RadarAction
+    data class CwToggleExpanded(val expanded: Boolean) : RadarAction
+    data class CwPermissionResult(val granted: Boolean) : RadarAction
 }

feature/radar/src/main/java/com/rtbishop/look4sat/feature/radar/RadarViewModel.kt

@@ -34,6 +34,7 @@ import com.rtbishop.look4sat.core.domain.repository.ISensorsRepo
 import com.rtbishop.look4sat.core.domain.repository.ISettingsRepo
 import com.rtbishop.look4sat.core.domain.sstv.LineRecoveryStrategy
 import com.rtbishop.look4sat.core.domain.sstv.SstvDecoder
+import com.rtbishop.look4sat.core.domain.cw.CwDecoder
 import com.rtbishop.look4sat.core.domain.usecase.IAudioCapture
 import com.rtbishop.look4sat.core.domain.usecase.IAddToCalendar
 import com.rtbishop.look4sat.core.domain.usecase.ISaveImage
@@ -70,6 +71,8 @@ class RadarViewModel(
     private var transponders: List<SatRadio> = emptyList()
     private var sstvDecoder: SstvDecoder? = null
     private var sstvRecordingJob: Job? = null
+    private var cwDecoder: CwDecoder? = null
+    private var cwListeningJob: Job? = null
 
     // Celestial positions change slowly, recompute at most once per minute
     private var lastCelestialUpdateMs = 0L
@@ -272,6 +275,25 @@ class RadarViewModel(
                 sstvDecoder?.clearPixels()
                 _uiState.update { it.copy(sstv = it.sstv.copy(currentFrame = null)) }
             }
+
+            // CW actions
+            is RadarAction.CwPermissionResult -> {
+                _uiState.update { it.copy(cw = it.cw.copy(hasPermission = action.granted)) }
+                if (action.granted) initCwDecoder()
+            }
+            RadarAction.CwStartListening -> startCwListening()
+            RadarAction.CwStopListening -> stopCwListening()
+            RadarAction.CwReset -> {
+                cwDecoder?.resetDecoder()
+                _uiState.update { it.copy(cw = it.cw.copy(decodedText = "")) }
+            }
+            is RadarAction.CwSetToneFreq -> {
+                _uiState.update { it.copy(cw = it.cw.copy(cwToneFreq = action.freq)) }
+                cwDecoder = CwDecoder(sampleRate = audioCapture.sampleRate, cwToneFreq = action.freq)
+            }
+            is RadarAction.CwToggleExpanded -> {
+                _uiState.update { it.copy(cw = it.cw.copy(isExpanded = action.expanded)) }
+            }
         }
     }
 
@@ -392,6 +414,48 @@ class RadarViewModel(
         _uiState.update { it.copy(sstv = it.sstv.copy(status = SstvStatus.Idle)) }
     }
 
+    private fun initCwDecoder() {
+        if (cwDecoder == null) {
+            cwDecoder = CwDecoder(
+                sampleRate = audioCapture.sampleRate,
+                cwToneFreq = _uiState.value.cw.cwToneFreq
+            )
+        }
+    }
+
+    private fun startCwListening() {
+        if (cwListeningJob?.isActive == true) return
+        // Stop SSTV if running (audio capture is shared)
+        stopSstvRecording()
+        initCwDecoder()
+        cwDecoder?.resetDecoder()
+        _uiState.update { it.copy(cw = it.cw.copy(status = CwStatus.Listening)) }
+        cwListeningJob = viewModelScope.launch {
+            // Collect decoded text flow
+            launch {
+                cwDecoder?.decodedTextFlow?.collect { text ->
+                    _uiState.update { it.copy(cw = it.cw.copy(decodedText = text)) }
+                }
+            }
+            // Collect signal strength
+            launch {
+                cwDecoder?.signalStrength?.collect { strength ->
+                    _uiState.update { it.copy(cw = it.cw.copy(signalStrength = strength)) }
+                }
+            }
+            // Capture audio and feed to decoder
+            audioCapture.audioFlow().collect { buffer ->
+                cwDecoder?.processBuffer(buffer)
+            }
+        }
+    }
+
+    private fun stopCwListening() {
+        cwListeningJob?.cancel()
+        cwListeningJob = null
+        _uiState.update { it.copy(cw = it.cw.copy(status = CwStatus.Idle)) }
+    }
+
     companion object {
         // SSTV Decoder Tuning Parameters
         // ==============================

feature/radar/src/main/java/com/rtbishop/look4sat/feature/radar/TransceiversPage.kt

@@ -40,10 +40,13 @@ import androidx.compose.foundation.lazy.itemsIndexed
 import androidx.compose.foundation.lazy.rememberLazyListState
 import androidx.compose.foundation.shape.CircleShape
 import androidx.compose.foundation.text.KeyboardOptions
+import androidx.compose.material3.Button
+import androidx.compose.material3.ElevatedCard
 import androidx.compose.material3.FilterChip
 import androidx.compose.material3.HorizontalDivider
 import androidx.compose.material3.Icon
 import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.OutlinedButton
 import androidx.compose.material3.OutlinedTextField
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
@@ -80,6 +83,7 @@ fun TransceiversPage(
     transceivers: List<SatRadio>,
     selectedUuid: String?,
     orbitalPos: OrbitalPos?,
+    cw: CwSubState,
     radioControl: RadioControlSubState,
     onAction: (RadarAction) -> Unit,
     modifier: Modifier = Modifier
@@ -105,6 +109,7 @@ fun TransceiversPage(
                     radio = radio,
                     isExpanded = isExpanded,
                     orbitalPos = orbitalPos,
+                    cw = cw,
                     radioControl = radioControl,
                     onAction = onAction,
                     onToggle = { onAction(RadarAction.SelectTransmitter(radio.uuid)) }
@@ -142,6 +147,7 @@ private fun TransceiverItem(
     radio: SatRadio,
     isExpanded: Boolean,
     orbitalPos: OrbitalPos?,
+    cw: CwSubState,
     radioControl: RadioControlSubState,
     onAction: (RadarAction) -> Unit,
     onToggle: () -> Unit
@@ -237,6 +243,7 @@ private fun TransceiverItem(
             ExpandedRadioControl(
                 radio = radio,
                 orbitalPos = orbitalPos,
+                cw = cw,
                 radioControl = radioControl,
                 onAction = onAction
             )
@@ -308,6 +315,7 @@ private fun UnifiedFrequencyRow(
 private fun ExpandedRadioControl(
     radio: SatRadio,
     orbitalPos: OrbitalPos?,
+    cw: CwSubState,
     radioControl: RadioControlSubState,
     onAction: (RadarAction) -> Unit
 ) {
@@ -425,6 +433,15 @@ private fun ExpandedRadioControl(
             modifier = Modifier.fillMaxWidth()
         )
 
+        // CW decoder panel (linear transponders only)
+        if (DopplerFrequencyCalculator.isLinearTransponder(radio)) {
+            CwDecoderPanel(
+                cw = cw,
+                onAction = onAction,
+                modifier = Modifier.fillMaxWidth()
+            )
+        }
+
         // Control buttons
         Row(horizontalArrangement = Arrangement.spacedBy(4.dp)) {
             if (!radioControl.txPanel.isConnected && !radioControl.rxPanel.isConnected) {
@@ -602,6 +619,113 @@ private fun DopplerFrequencyCalculator(
 
 private enum class EditedField { TX, RX }
 
+@Composable
+private fun CwDecoderPanel(
+    cw: CwSubState,
+    onAction: (RadarAction) -> Unit,
+    modifier: Modifier = Modifier
+) {
+    Column(
+        modifier = modifier,
+        verticalArrangement = Arrangement.spacedBy(4.dp)
+    ) {
+        // Header row: expand/collapse toggle
+        Row(
+            modifier = Modifier
+                .fillMaxWidth()
+                .clickable { onAction(RadarAction.CwToggleExpanded(!cw.isExpanded)) },
+            horizontalArrangement = Arrangement.SpaceBetween,
+            verticalAlignment = Alignment.CenterVertically
+        ) {
+            Text(
+                text = stringResource(R.string.radar_cw_decoder),
+                fontSize = 14.sp,
+                fontWeight = FontWeight.Medium,
+                color = MaterialTheme.colorScheme.primary
+            )
+            Icon(
+                painter = painterResource(id = R.drawable.ic_arrow),
+                contentDescription = null,
+                tint = MaterialTheme.colorScheme.onSurfaceVariant,
+                modifier = Modifier
+                    .size(20.dp)
+                    .rotate(if (cw.isExpanded) 270f else 90f)
+            )
+        }
+
+        AnimatedVisibility(visible = cw.isExpanded) {
+            Column(verticalArrangement = Arrangement.spacedBy(8.dp)) {
+                // Control buttons row
+                Row(
+                    horizontalArrangement = Arrangement.spacedBy(8.dp),
+                    modifier = Modifier.fillMaxWidth()
+                ) {
+                    if (cw.status == CwStatus.Idle) {
+                        Button(
+                            onClick = { onAction(RadarAction.CwStartListening) },
+                            modifier = Modifier.weight(1f)
+                        ) {
+                            Text(stringResource(R.string.radar_cw_start))
+                        }
+                    } else {
+                        Button(
+                            onClick = { onAction(RadarAction.CwStopListening) },
+                            modifier = Modifier.weight(1f)
+                        ) {
+                            Text(stringResource(R.string.radar_cw_stop))
+                        }
+                    }
+                    OutlinedButton(
+                        onClick = { onAction(RadarAction.CwReset) },
+                        modifier = Modifier.weight(1f)
+                    ) {
+                        Text(stringResource(R.string.radar_cw_reset))
+                    }
+                }
+
+                // Signal strength indicator
+                if (cw.status == CwStatus.Listening && cw.signalStrength > 0f) {
+                    val strengthPct = (cw.signalStrength * 100).toInt()
+                    Text(
+                        text = "Signal: $strengthPct%",
+                        fontSize = 12.sp,
+                        color = if (cw.signalStrength > 0.5f) Color(0xFF4CAF50)
+                        else if (cw.signalStrength > 0.2f) Color(0xFFFFC107)
+                        else MaterialTheme.colorScheme.onSurfaceVariant
+                    )
+                }
+
+                // Decoded text output
+                ElevatedCard(
+                    modifier = Modifier
+                        .fillMaxWidth()
+                        .height(120.dp)
+                ) {
+                    Column(
+                        modifier = Modifier
+                            .fillMaxSize()
+                            .padding(8.dp)
+                    ) {
+                        Text(
+                            text = "Decoded:",
+                            fontSize = 12.sp,
+                            fontWeight = FontWeight.Bold,
+                            color = MaterialTheme.colorScheme.onSurfaceVariant
+                        )
+                        Spacer(modifier = Modifier.height(4.dp))
+                        Text(
+                            text = cw.decodedText.ifEmpty { "Waiting for CW signal..." },
+                            fontSize = 16.sp,
+                            fontWeight = FontWeight.Medium,
+                            color = MaterialTheme.colorScheme.onSurface
+                        )
+                    }
+                }
+            }
+        }
+    }
+}
+
 @Composable
 private fun FrequencyText(frequency: Long?, modifier: Modifier = Modifier) {
     val text = frequency?.let {