[feat](trx-frontend-http): refine SDR bandwidth control

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

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

@@ -1561,10 +1561,22 @@ function formatBwLabel(hz) {
 // Current receive bandwidth (Hz) — updated by server sync and BW drag.
 let currentBandwidthHz = 3_000;
 const spectrumBwInput = document.getElementById("spectrum-bw-input");
+const spectrumBwSetBtn = document.getElementById("spectrum-bw-set-btn");
+
+function formatBandwidthInputKhz(hz) {
+  const khz = hz / 1000;
+  if (Math.abs(Math.round(khz) - khz) < 0.0001) return String(Math.round(khz));
+  if (Math.abs(Math.round(khz * 10) - khz * 10) < 0.0001) return khz.toFixed(1);
+  return khz.toFixed(2);
+}
 
 function syncBandwidthInput(hz) {
   if (!spectrumBwInput || !Number.isFinite(hz) || hz <= 0) return;
-  spectrumBwInput.value = String(Math.round(hz));
+  const [, minBw, maxBw, stepBw] = mwDefaultsForMode(modeEl ? modeEl.value : "USB");
+  spectrumBwInput.min = String(minBw / 1000);
+  spectrumBwInput.max = String(maxBw / 1000);
+  spectrumBwInput.step = String(stepBw / 1000);
+  spectrumBwInput.value = formatBandwidthInputKhz(hz);
 }
 
 // Apply mode-specific BW default and optionally push to server.
@@ -1580,7 +1592,8 @@ async function applyBwDefaultForMode(mode, sendToServer) {
 async function applyBandwidthFromInput() {
   if (!spectrumBwInput) return;
   const [, minBw, maxBw] = mwDefaultsForMode(modeEl ? modeEl.value : "USB");
-  const next = Math.round(Number(spectrumBwInput.value));
+  const nextKhz = Number(spectrumBwInput.value);
+  const next = Math.round(nextKhz * 1000);
   if (!Number.isFinite(next) || next <= 0) {
     syncBandwidthInput(currentBandwidthHz);
     return;
@@ -1593,7 +1606,6 @@ async function applyBandwidthFromInput() {
 }
 
 if (spectrumBwInput) {
-  spectrumBwInput.addEventListener("change", () => { applyBandwidthFromInput(); });
   spectrumBwInput.addEventListener("keydown", (e) => {
     if (e.key === "Enter") {
       e.preventDefault();
@@ -1601,6 +1613,9 @@ if (spectrumBwInput) {
     }
   });
 }
+if (spectrumBwSetBtn) {
+  spectrumBwSetBtn.addEventListener("click", () => { applyBandwidthFromInput(); });
+}
 
 // --- Tab navigation ---
 document.querySelector(".tab-bar").addEventListener("click", (e) => {

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

@@ -65,7 +65,10 @@
         <div id="spectrum-freq-axis"></div>
       </div>
       <div id="spectrum-controls">
-        <label id="spectrum-bw-label">Bandwidth <input type="number" id="spectrum-bw-input" value="" step="100" min="1" /> Hz</label>
+        <div id="spectrum-bw-row">
+          <label id="spectrum-bw-label">Bandwidth <input type="number" id="spectrum-bw-input" value="" step="0.1" min="0.1" /> kHz</label>
+          <button id="spectrum-bw-set-btn" type="button">Set</button>
+        </div>
         <div id="spectrum-level-row">
           <label id="spectrum-floor-label">Floor <input type="number" id="spectrum-floor-input" value="-100" step="5" /> dB</label>
           <button id="spectrum-auto-btn" type="button">Auto</button>

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

@@ -653,17 +653,21 @@ button:focus-visible, input:focus-visible, select:focus-visible {
   font-size: 0.78rem;
   color: var(--text-muted);
 }
+#spectrum-bw-row {
+  display: flex;
+  align-items: center;
+  gap: 0.4rem;
+}
 #spectrum-bw-label {
   display: flex;
   align-items: center;
   gap: 0.3rem;
-  font-size: 0.78rem;
-  color: var(--accent-yellow);
-  font-weight: 600;
+  font-size: 0.75rem;
+  color: var(--text-muted);
   min-width: 0;
 }
 #spectrum-bw-input {
-  width: 5.25rem;
+  width: 4.5rem;
   padding: 1px 4px;
   font-size: 0.75rem;
   border: 1px solid var(--border);
@@ -673,6 +677,12 @@ button:focus-visible, input:focus-visible, select:focus-visible {
   text-align: right;
   height: 1.5rem;
 }
+#spectrum-bw-set-btn {
+  height: 1.5rem;
+  min-height: 0;
+  padding: 0 8px;
+  font-size: 0.73rem;
+}
 #spectrum-level-row {
   display: flex;
   align-items: center;