diff --git a/static/css/components/signal-waveform.css b/static/css/components/signal-waveform.css
new file mode 100644
index 0000000..2b5c6ec
--- /dev/null
+++ b/static/css/components/signal-waveform.css
@@ -0,0 +1,39 @@
+/**
+ * Signal Waveform Component
+ * Animated SVG bar waveform for indicating live signal activity
+ */
+
+.signal-waveform {
+    display: inline-flex;
+    align-items: center;
+    vertical-align: middle;
+}
+
+.signal-waveform-svg {
+    display: block;
+}
+
+.signal-waveform-bar {
+    will-change: height, y;
+    transition: fill 0.3s ease;
+}
+
+/* Idle breathing animation */
+.signal-waveform.idle .signal-waveform-bar {
+    animation: signal-waveform-breathe 2.5s ease-in-out infinite;
+}
+
+.signal-waveform.idle .signal-waveform-bar:nth-child(even) {
+    animation-delay: -1.25s;
+}
+
+@keyframes signal-waveform-breathe {
+    0%, 100% { opacity: 0.4; }
+    50% { opacity: 0.7; }
+}
+
+/* Active state - disable CSS breathing, JS drives heights */
+.signal-waveform.active .signal-waveform-bar {
+    animation: none;
+    opacity: 1;
+}
diff --git a/static/js/components/signal-waveform.js b/static/js/components/signal-waveform.js
new file mode 100644
index 0000000..d06750e
--- /dev/null
+++ b/static/js/components/signal-waveform.js
@@ -0,0 +1,184 @@
+/**
+ * Signal Waveform Component
+ * Animated SVG bar waveform showing live signal activity.
+ * Flat/breathing when idle, oscillates on incoming data.
+ */
+
+const SignalWaveform = (function() {
+    'use strict';
+
+    const DEFAULT_CONFIG = {
+        width: 200,
+        height: 40,
+        barCount: 24,
+        color: '#00e5ff',
+        decayMs: 3000,
+        idleAmplitude: 0.05,
+    };
+
+    class Live {
+        constructor(container, config = {}) {
+            this.container = typeof container === 'string'
+                ? document.querySelector(container)
+                : container;
+            this.config = { ...DEFAULT_CONFIG, ...config };
+            this.lastPingTime = 0;
+            this.pingTimestamps = [];
+            this.animFrameId = null;
+            this.phase = 0;
+            this.targetHeights = [];
+            this.currentHeights = [];
+            this.stopped = false;
+
+            this._buildSvg();
+            this._startLoop();
+        }
+
+        /** Signal that a telemetry message arrived */
+        ping() {
+            const now = performance.now();
+            this.lastPingTime = now;
+            this.pingTimestamps.push(now);
+            this.stopped = false;
+            // Randomise target heights on each ping
+            this._randomiseTargets();
+        }
+
+        /** Transition to idle */
+        stop() {
+            this.stopped = true;
+            this.lastPingTime = 0;
+            this.pingTimestamps = [];
+        }
+
+        /** Tear down animation loop and DOM */
+        destroy() {
+            if (this.animFrameId) {
+                cancelAnimationFrame(this.animFrameId);
+                this.animFrameId = null;
+            }
+            if (this.container) {
+                this.container.innerHTML = '';
+            }
+        }
+
+        // -- Private --
+
+        _buildSvg() {
+            if (!this.container) return;
+            const { width, height, barCount, color } = this.config;
+            const gap = 1;
+            const barWidth = (width - gap * (barCount - 1)) / barCount;
+            const minH = height * this.config.idleAmplitude;
+
+            const ns = 'http://www.w3.org/2000/svg';
+            const svg = document.createElementNS(ns, 'svg');
+            svg.setAttribute('class', 'signal-waveform-svg');
+            svg.setAttribute('width', width);
+            svg.setAttribute('height', height);
+            svg.setAttribute('viewBox', `0 0 ${width} ${height}`);
+
+            this.bars = [];
+            for (let i = 0; i < barCount; i++) {
+                const rect = document.createElementNS(ns, 'rect');
+                const x = i * (barWidth + gap);
+                rect.setAttribute('x', x.toFixed(1));
+                rect.setAttribute('y', (height - minH).toFixed(1));
+                rect.setAttribute('width', barWidth.toFixed(1));
+                rect.setAttribute('height', minH.toFixed(1));
+                rect.setAttribute('rx', '1');
+                rect.setAttribute('fill', color);
+                rect.setAttribute('class', 'signal-waveform-bar');
+                svg.appendChild(rect);
+                this.bars.push(rect);
+                this.currentHeights.push(minH);
+                this.targetHeights.push(minH);
+            }
+
+            const wrapper = document.createElement('div');
+            wrapper.className = 'signal-waveform idle';
+            wrapper.appendChild(svg);
+            this.container.innerHTML = '';
+            this.container.appendChild(wrapper);
+            this.wrapperEl = wrapper;
+        }
+
+        _randomiseTargets() {
+            const { height } = this.config;
+            const amplitude = this._getAmplitude();
+            for (let i = 0; i < this.config.barCount; i++) {
+                // Sine envelope with randomisation
+                const envelope = Math.sin(Math.PI * i / (this.config.barCount - 1));
+                const rand = 0.4 + Math.random() * 0.6;
+                this.targetHeights[i] = Math.max(
+                    height * this.config.idleAmplitude,
+                    height * amplitude * envelope * rand
+                );
+            }
+        }
+
+        _getAmplitude() {
+            if (this.stopped) return this.config.idleAmplitude;
+            const now = performance.now();
+            const elapsed = now - this.lastPingTime;
+            if (this.lastPingTime === 0 || elapsed > this.config.decayMs) {
+                return this.config.idleAmplitude;
+            }
+
+            // Prune old timestamps (keep last 5s)
+            const cutoff = now - 5000;
+            this.pingTimestamps = this.pingTimestamps.filter(t => t > cutoff);
+
+            // Base amplitude from ping frequency (more pings = higher amplitude)
+            const freq = this.pingTimestamps.length / 5; // pings per second
+            const freqAmp = Math.min(1, 0.3 + freq * 0.35);
+
+            // Decay factor
+            const decay = 1 - (elapsed / this.config.decayMs);
+            return Math.max(this.config.idleAmplitude, freqAmp * decay);
+        }
+
+        _startLoop() {
+            const tick = () => {
+                this.animFrameId = requestAnimationFrame(tick);
+                this._update();
+            };
+            this.animFrameId = requestAnimationFrame(tick);
+        }
+
+        _update() {
+            if (!this.bars || !this.bars.length) return;
+            const { height } = this.config;
+            const minH = height * this.config.idleAmplitude;
+            const amplitude = this._getAmplitude();
+            const isActive = amplitude > this.config.idleAmplitude * 1.5;
+
+            // Toggle CSS class for breathing vs active
+            if (this.wrapperEl) {
+                this.wrapperEl.classList.toggle('idle', !isActive);
+                this.wrapperEl.classList.toggle('active', isActive);
+            }
+
+            // When idle, slowly drift targets with phase
+            if (!isActive) {
+                this.phase += 0.02;
+                for (let i = 0; i < this.bars.length; i++) {
+                    this.targetHeights[i] = minH;
+                }
+            }
+
+            // Lerp current toward target
+            const lerp = isActive ? 0.18 : 0.06;
+            for (let i = 0; i < this.bars.length; i++) {
+                this.currentHeights[i] += (this.targetHeights[i] - this.currentHeights[i]) * lerp;
+                const h = Math.max(minH, this.currentHeights[i]);
+                this.bars[i].setAttribute('height', h.toFixed(1));
+                this.bars[i].setAttribute('y', (height - h).toFixed(1));
+            }
+        }
+    }
+
+    return { Live };
+})();
+
+window.SignalWaveform = SignalWaveform;
diff --git a/templates/index.html b/templates/index.html
index ef6ff78..6edad8d 100644
--- a/templates/index.html
+++ b/templates/index.html
@@ -66,6 +66,7 @@
     <link rel="stylesheet" href="{{ url_for('static', filename='css/components/function-strip.css') }}">
     <link rel="stylesheet" href="{{ url_for('static', filename='css/components/toast.css') }}">
     <link rel="stylesheet" href="{{ url_for('static', filename='css/components/ux-platform.css') }}">
+    <link rel="stylesheet" href="{{ url_for('static', filename='css/components/signal-waveform.css') }}">
     <link rel="stylesheet" href="{{ url_for('static', filename='css/core/components.css') }}">
     <link rel="stylesheet" href="{{ url_for('static', filename='css/modes/waterfall.css') }}?v={{ version }}&r=wfdeck19">
     <script>
@@ -3245,6 +3246,7 @@
     <script src="{{ url_for('static', filename='js/components/device-card.js') }}"></script>
     <script src="{{ url_for('static', filename='js/components/proximity-radar.js') }}"></script>
     <script src="{{ url_for('static', filename='js/components/timeline-heatmap.js') }}"></script>
+    <script src="{{ url_for('static', filename='js/components/signal-waveform.js') }}"></script>
     <script src="{{ url_for('static', filename='js/modes/bluetooth.js') }}?v={{ version }}&r=btlocate1"></script>
     <!-- WiFi v2 components -->
     <script src="{{ url_for('static', filename='js/components/channel-chart.js') }}"></script>
@@ -4457,6 +4459,7 @@
             } else if (mode === 'morse') {
                 MorseMode.init();
             } else if (mode === 'radiosonde') {
+                initRadiosondeWaveform();
                 initRadiosondeMap();
                 setTimeout(() => {
                     if (radiosondeMap) radiosondeMap.invalidateSize();
diff --git a/templates/partials/modes/radiosonde.html b/templates/partials/modes/radiosonde.html
index fa3c4e3..cad99f0 100644
--- a/templates/partials/modes/radiosonde.html
+++ b/templates/partials/modes/radiosonde.html
@@ -35,6 +35,7 @@
 
     <div class="section">
         <h3>Status</h3>
+        <div id="radiosondeWaveformContainer" style="margin-bottom: 8px;"></div>
         <div id="radiosondeStatusDisplay" class="info-text">
             <p>Status: <span id="radiosondeStatusText" style="color: var(--accent-yellow);">Standby</span></p>
             <p>Balloons: <span id="radiosondeBalloonCount">0</span></p>
@@ -108,6 +109,24 @@
 <script>
     let radiosondeEventSource = null;
     let radiosondeBalloons = {};
+    let radiosondeWaveform = null;
+
+    // Initialise signal waveform once the component script has loaded
+    function initRadiosondeWaveform() {
+        if (radiosondeWaveform) return;
+        if (typeof SignalWaveform === 'undefined') return;
+        const el = document.getElementById('radiosondeWaveformContainer');
+        if (el) {
+            radiosondeWaveform = new SignalWaveform.Live(el, {
+                width: 200,
+                height: 40,
+                barCount: 24,
+                color: '#00e5ff',
+                decayMs: 3000,
+                idleAmplitude: 0.05,
+            });
+        }
+    }
 
     function updateRadiosondeFreqRange() {
         const region = document.getElementById('radiosondeRegionSelect').value;
@@ -152,7 +171,12 @@
                 longitude: radiosondeStationLocation.lon,
             })
         })
-        .then(r => r.json())
+        .then(r => {
+            if (!r.ok && r.headers.get('content-type')?.indexOf('application/json') === -1) {
+                throw new Error(`Server error (${r.status}). Check that the backend is running.`);
+            }
+            return r.json();
+        })
         .then(data => {
             if (data.status === 'started' || data.status === 'already_running') {
                 document.getElementById('startRadiosondeBtn').style.display = 'none';
@@ -178,6 +202,7 @@
             radiosondeEventSource.close();
             radiosondeEventSource = null;
         }
+        if (radiosondeWaveform) radiosondeWaveform.stop();
 
         fetch('/radiosonde/stop', { method: 'POST' })
         .then(r => r.json())
@@ -207,6 +232,7 @@
             try {
                 const data = JSON.parse(e.data);
                 if (data.type === 'balloon') {
+                    if (radiosondeWaveform) radiosondeWaveform.ping();
                     radiosondeBalloons[data.id] = data;
                     document.getElementById('radiosondeBalloonCount').textContent = Object.keys(radiosondeBalloons).length;
                     const now = new Date();