https://warriorlifepodcast.com/demo/demo-waterfall.js?v=6ddc9c6663be

1/* Synthetic FT8 spectrum: visual simulation, not encoded or transmitted audio.
2 * Timing and tone spacing follow the WSJT-X FT8 protocol description.
3 */
4(() => {
5  "use strict";
6  const stations = [
7    [356, .65, 0], [822, .88, 1], [1076, .4, 0], [1456, .73, 1],
8    [1860, .48, 0], [2226, .65, 1], [2336, .9, 0], [2856, .54, 1],
9    [465, .8, 1], [610, .65, 0], [715, .85, 1], [940, .6, 0],
10    [1190, .95, 1], [1320, .7, 0], [1570, .85, 0], [1690, .6, 1],
11    [1980, .9, 1], [2110, .55, 0], [2490, .75, 1], [2660, .6, 0]
12  ];
13  const maximumHz = 3000;
14  const rowSeconds = .4;
15  function noise(seed) {
16    let value = Math.imul(seed ^ 0x9e3779b9, 0x85ebca6b);
17    value = Math.imul(value ^ (value >>> 13), 0xc2b2ae35);
18    return ((value ^ (value >>> 16)) >>> 0) / 4294967296;
19  }
20  function signalAt(seconds, index) {
21    const [base, strength, parity] = stations[index];
22    const mode = window.dccDemoStation?.mode || "FT8";
23    const period = mode === "FT4" ? 7.5 : mode === "WSPR" ? 120 : 15;
24    const duration = mode === "FT4" ? 5.04 : mode === "WSPR" ? 110.6 : 12.64;
25    const symbolTime = mode === "FT4" ? .048 : mode === "WSPR" ? .682667 : mode === "RTTY" ? 1/45.45 : .16;
26    const slot = Math.floor(seconds / period);
27    const elapsed = seconds - slot * period - .5;
28    if (elapsed < 0 || elapsed >= duration || ((slot % 2) + 2) % 2 !== parity) return null;
29    const symbol = Math.floor(elapsed / symbolTime);
30    const tones = mode === "RTTY" ? 2 : ["FT4","WSPR"].includes(mode) ? 4 : mode === "PSK31" ? 1 : 8;
31    const spacing = mode === "FT4" ? 20.8333 : mode === "WSPR" ? 1.4648 : mode === "RTTY" ? 170 : 6.25;
32    const tone = Math.floor(noise(index * 100003 + slot * 101 + symbol * 7919) * tones);
33    const fade = .8 + .2 * Math.sin(seconds * .9 + index);
34    return {hz: (mode === "WSPR" ? 1410 + index*8 : base) + tone * spacing, amplitude: strength * fade, symbol};
35  }
36  function spectrumAt(seconds, width) {
37    const values = new Float32Array(width);
38    const row = Math.floor(seconds / rowSeconds);
39    for (let x = 0; x < width; x++) {
40      values[x] = .045 + .045 * noise(row * 10007 + x * 37) + .01 * Math.sin(x / 70);
41    }
42    stations.forEach((station, index) => {
43      // Integrate several symbols. Single-pixel instantaneous tones disappear
44      // when the app scales its canvas down to the compact waterfall panel.
45      for (const sample of [seconds, seconds - .16, seconds - .32, seconds - .48]) {
46        const signal = signalAt(sample, index);
47        if (!signal) continue;
48        const center = signal.hz / maximumHz * width;
49        const sigma = Math.max(1.1, 5 / maximumHz * width);
50        for (let x = Math.max(0, Math.floor(center - sigma * 4)); x < Math.min(width, Math.ceil(center + sigma * 4)); x++) {
51          const distance = (x - center) / sigma;
52          const texture = .85 + .3 * noise(row * 97 + x * 13 + index * 7919);
53          values[x] += .55 * signal.amplitude * texture * Math.exp(-.5 * distance * distance);
54        }
55      }
56    });
57    return values;
58  }
59  const palette = [[0, [1, 5, 12]], [.1, [7, 21, 45]], [.2, [0, 85, 150]], [.32, [55, 200, 100]], [.45, [245, 238, 20]], [.7, [255, 120, 0]], [1, [240, 20, 10]]];
60  function color(value) {
61    const level = Math.max(0, Math.min(1, value));
62    const upper = palette.findIndex(stop => stop[0] >= level);
63    if (upper <= 0) return palette[0][1];
64    const [low, a] = palette[upper - 1];
65    const [high, b] = palette[upper];
66    return a.map((channel, index) => Math.round(channel + (b[index] - channel) * (level - low) / (high - low)));
67  }
68  window.dccDemoWaterfall = {spectrumAt, signalAt, color, maximumHz, rowSeconds};
69})();