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+# Signal Identification Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Build a bundled JSON signal database (~500 entries) with a scored match API route and a standalone modal overlay accessible from the waterfall and global nav.
+
+**Architecture:** `utils/signal_db.py` loads `data/signals.json` once at startup (lazy, cached). `routes/signalid.py` gains `POST /signalid/match` which calls the pure match function. `static/js/components/signal-id-modal.js` is a standalone IIFE modal called from both `waterfall.js` and a new nav button in `templates/partials/nav.html`.
+
+**Tech Stack:** Python 3.11+, Flask blueprints, vanilla JS (IIFE), JSON data file, existing CSS variables.
+
+## Global Constraints
+
+- All modulation tokens in `signals.json` must be uppercase strings (`WFM`, `FM`, `AM`, `USB`, `LSB`, `NFM`, `FSK`, `OOK`, `PSK`, etc.)
+- All frequencies in `signals.json` stored as integers in Hz
+- Match scores are 0–100 integer points
+- Route added to existing `signalid_bp` blueprint in `routes/signalid.py`; no new blueprint
+- No new Python dependencies — stdlib only
+- JS follows IIFE pattern consistent with other components: `window.SignalIdModal = (function() { ... })()`
+- Modal styled with existing CSS variables only (`--bg-card`, `--accent-cyan`, `--font-mono`, `--text-primary`, `--text-muted`, `--text-secondary`, `--accent-red`, `--bg-input`)
+- `signal-id-modal.js` goes in `static/js/components/` (eagerly loaded, not lazy-loaded per mode)
+
+---
+
+## File Map
+
+| Action | File | Responsibility |
+|---|---|---|
+| Create | `data/signals.json` | Bundled signal database |
+| Create | `utils/signal_db.py` | Load + cache signals.json; pure `match_signals()` function |
+| Create | `tests/test_signals_json.py` | Schema validation for every entry in signals.json |
+| Create | `tests/test_signalid_match.py` | Unit tests for matching algorithm |
+| Create | `static/js/components/signal-id-modal.js` | Signal ID modal IIFE component |
+| Modify | `routes/signalid.py` | Add `POST /signalid/match` route |
+| Modify | `config.py` | Add `REGION = _get_env("REGION", "GLOBAL")` |
+| Modify | `templates/index.html` | Add eager `<script>` tag for `signal-id-modal.js` |
+| Modify | `templates/partials/nav.html` | Add "Signal ID" button in Intel group |
+| Modify | `templates/partials/modes/waterfall.html` | Replace Signal ID sidebar panel with single "Identify Signal" button |
+| Modify | `static/js/modes/waterfall.js` | Wire "Identify Signal" button and `handoff('signalid')` to `SignalIdModal.open()` |
+
+---
+
+## Task 1: signals.json seed database + schema validation test
+
+**Files:**
+- Create: `data/signals.json`
+- Create: `tests/test_signals_json.py`
+
+**Interfaces:**
+- Produces: `data/signals.json` — JSON array of signal objects consumed by `utils/signal_db.py` in Task 2
+
+- [ ] **Step 1: Write the schema validation test**
+
+Create `tests/test_signals_json.py`:
+
+```python
+"""Schema validation for data/signals.json."""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+
+SIGNALS_PATH = Path(__file__).resolve().parent.parent / "data" / "signals.json"
+
+VALID_REGIONS = {"GLOBAL", "EU", "US", "UK", "AU"}
+
+
+def _load() -> list[dict]:
+    assert SIGNALS_PATH.exists(), f"signals.json not found at {SIGNALS_PATH}"
+    with open(SIGNALS_PATH) as f:
+        data = json.load(f)
+    assert isinstance(data, list), "signals.json must be a JSON array"
+    return data
+
+
+class TestSignalsJsonSchema:
+    def test_file_loads_as_list(self):
+        data = _load()
+        assert len(data) > 0
+
+    def test_all_ids_unique(self):
+        data = _load()
+        ids = [s["id"] for s in data]
+        assert len(ids) == len(set(ids)), f"Duplicate ids: {[x for x in ids if ids.count(x) > 1]}"
+
+    def test_required_string_fields(self):
+        data = _load()
+        for s in data:
+            for field in ("id", "name", "description"):
+                assert field in s, f"Missing '{field}' in signal {s.get('id', '?')}"
+                assert isinstance(s[field], str), f"'{field}' must be str in {s['id']}"
+                assert s[field].strip(), f"'{field}' must not be empty in {s['id']}"
+
+    def test_frequency_ranges_valid(self):
+        data = _load()
+        for s in data:
+            sid = s.get("id", "?")
+            assert "frequency_ranges" in s, f"Missing frequency_ranges in {sid}"
+            assert isinstance(s["frequency_ranges"], list), f"frequency_ranges must be list in {sid}"
+            assert len(s["frequency_ranges"]) > 0, f"frequency_ranges must not be empty in {sid}"
+            for r in s["frequency_ranges"]:
+                assert isinstance(r.get("min_hz"), int), f"min_hz must be int in {sid}"
+                assert isinstance(r.get("max_hz"), int), f"max_hz must be int in {sid}"
+                assert r["min_hz"] > 0, f"min_hz must be > 0 in {sid}"
+                assert r["min_hz"] < r["max_hz"], f"min_hz must be < max_hz in {sid}"
+
+    def test_bandwidth_range_valid_or_null(self):
+        data = _load()
+        for s in data:
+            sid = s.get("id", "?")
+            assert "bandwidth_range" in s, f"Missing bandwidth_range in {sid}"
+            bw = s["bandwidth_range"]
+            if bw is None:
+                continue
+            assert isinstance(bw.get("min_hz"), int), f"bandwidth_range.min_hz must be int in {sid}"
+            assert isinstance(bw.get("max_hz"), int), f"bandwidth_range.max_hz must be int in {sid}"
+            assert bw["min_hz"] > 0, f"bandwidth_range.min_hz must be > 0 in {sid}"
+            assert bw["min_hz"] < bw["max_hz"], f"bandwidth_range.min_hz must be < max_hz in {sid}"
+
+    def test_modulations_uppercase_strings(self):
+        data = _load()
+        for s in data:
+            sid = s.get("id", "?")
+            assert "modulations" in s, f"Missing modulations in {sid}"
+            assert isinstance(s["modulations"], list), f"modulations must be list in {sid}"
+            for m in s["modulations"]:
+                assert isinstance(m, str), f"modulation token must be str in {sid}"
+                assert m == m.upper(), f"modulation '{m}' must be uppercase in {sid}"
+                assert m.strip(), f"modulation token must not be empty in {sid}"
+
+    def test_categories_list_of_strings(self):
+        data = _load()
+        for s in data:
+            sid = s.get("id", "?")
+            assert "categories" in s, f"Missing categories in {sid}"
+            assert isinstance(s["categories"], list), f"categories must be list in {sid}"
+            for c in s["categories"]:
+                assert isinstance(c, str) and c.strip(), f"category must be non-empty str in {sid}"
+
+    def test_regions_valid_values(self):
+        data = _load()
+        for s in data:
+            sid = s.get("id", "?")
+            assert "regions" in s, f"Missing regions in {sid}"
+            assert isinstance(s["regions"], list), f"regions must be list in {sid}"
+            assert len(s["regions"]) > 0, f"regions must not be empty in {sid}"
+            for r in s["regions"]:
+                assert r in VALID_REGIONS, f"Invalid region '{r}' in {sid}. Valid: {VALID_REGIONS}"
+
+    def test_sigidwiki_url_string_or_null(self):
+        data = _load()
+        for s in data:
+            sid = s.get("id", "?")
+            assert "sigidwiki_url" in s, f"Missing sigidwiki_url in {sid}"
+            url = s["sigidwiki_url"]
+            if url is not None:
+                assert isinstance(url, str), f"sigidwiki_url must be str or null in {sid}"
+                assert url.startswith("https://www.sigidwiki.com/"), f"sigidwiki_url must be sigidwiki.com URL in {sid}"
+```
+
+- [ ] **Step 2: Run test — expect file-not-found failure**
+
+```bash
+cd /Users/admin/Dev/intercept && pytest tests/test_signals_json.py -v 2>&1 | head -20
+```
+
+Expected: `AssertionError: signals.json not found`
+
+- [ ] **Step 3: Create data/signals.json with initial seed**
+
+Create `data/signals.json` with the 20 signals migrated from `utils/signal_guess.py` (frequency ranges sourced from that file). The full initial seed to write:
+
+```json
+[
+  {
+    "id": "fm-broadcast",
+    "name": "FM Broadcast Radio",
+    "description": "Commercial FM radio stations transmitting wideband stereo audio. Used worldwide for public broadcasting.",
+    "categories": ["broadcast", "commercial", "audio"],
+    "frequency_ranges": [{"min_hz": 87500000, "max_hz": 108000000}],
+    "bandwidth_range": {"min_hz": 150000, "max_hz": 250000},
+    "modulations": ["WFM", "FM"],
+    "regions": ["GLOBAL"],
+    "sigidwiki_url": "https://www.sigidwiki.com/wiki/FM_Broadcast"
+  },
+  {
+    "id": "airband-civil",
+    "name": "Airband (Civil Aviation Voice)",
+    "description": "Civil aviation voice communications between pilots and air traffic control. AM modulated.",
+    "categories": ["aviation", "voice", "aeronautical"],
+    "frequency_ranges": [{"min_hz": 118000000, "max_hz": 137000000}],
+    "bandwidth_range": {"min_hz": 6000, "max_hz": 10000},
+    "modulations": ["AM"],
+    "regions": ["GLOBAL"],
+    "sigidwiki_url": "https://www.sigidwiki.com/wiki/AM_Aviation"
+  },
+  {
+    "id": "ism-433-eu",
+    "name": "ISM Device (433 MHz EU)",
+    "description": "Industrial, Scientific, and Medical band short-range devices — weather stations, remote controls, car key fobs, doorbells.",
+    "categories": ["ism", "telemetry", "consumer", "short-range"],
+    "frequency_ranges": [{"min_hz": 433050000, "max_hz": 434790000}],
+    "bandwidth_range": {"min_hz": 10000, "max_hz": 50000},
+    "modulations": ["OOK", "ASK", "FSK", "NFM", "FM"],
+    "regions": ["EU", "UK", "AU"],
+    "sigidwiki_url": null
+  },
+  {
+    "id": "ism-315-us",
+    "name": "ISM Device (315 MHz US)",
+    "description": "US ISM band short-range devices — garage openers, remote controls, tire pressure monitors.",
+    "categories": ["ism", "telemetry", "consumer", "short-range"],
+    "frequency_ranges": [{"min_hz": 314000000, "max_hz": 316000000}],
+    "bandwidth_range": {"min_hz": 10000, "max_hz": 50000},
+    "modulations": ["OOK", "ASK", "FSK"],
+    "regions": ["US"],
+    "sigidwiki_url": null
+  },
+  {
+    "id": "ism-868-eu",
+    "name": "ISM Device (868 MHz EU)",
+    "description": "EU sub-GHz ISM band used for LoRa, Z-Wave, smart metering, and IoT sensors.",
+    "categories": ["ism", "iot", "lora", "telemetry"],
+    "frequency_ranges": [{"min_hz": 863000000, "max_hz": 870000000}],
+    "bandwidth_range": {"min_hz": 200, "max_hz": 500000},
+    "modulations": ["FSK", "GFSK", "LORA", "OOK"],
+    "regions": ["EU", "UK"],
+    "sigidwiki_url": null
+  },
+  {
+    "id": "ism-915-us",
+    "name": "ISM Device (915 MHz US)",
+    "description": "US 915 MHz ISM band used for LoRa, Zigbee, smart meters, and IoT devices.",
+    "categories": ["ism", "iot", "lora", "telemetry"],
+    "frequency_ranges": [{"min_hz": 902000000, "max_hz": 928000000}],
+    "bandwidth_range": {"min_hz": 200, "max_hz": 500000},
+    "modulations": ["FSK", "GFSK", "LORA", "OOK"],
+    "regions": ["US"],
+    "sigidwiki_url": null
+  },
+  {
+    "id": "pmr446",
+    "name": "PMR446 (Licence-Free UHF)",
+    "description": "European licence-free walkie-talkie band. Used by hikers, event staff, and light commercial users.",
+    "categories": ["voice", "pmr", "consumer"],
+    "frequency_ranges": [{"min_hz": 446006250, "max_hz": 446193750}],
+    "bandwidth_range": {"min_hz": 10000, "max_hz": 15000},
+    "modulations": ["NFM", "FM"],
+    "regions": ["EU", "UK"],
+    "sigidwiki_url": "https://www.sigidwiki.com/wiki/PMR446"
+  },
+  {
+    "id": "frs-gmrs",
+    "name": "FRS/GMRS (US Licence-Free UHF)",
+    "description": "US Family Radio Service and General Mobile Radio Service. Common consumer walkie-talkie channels.",
+    "categories": ["voice", "consumer"],
+    "frequency_ranges": [{"min_hz": 462550000, "max_hz": 467725000}],
+    "bandwidth_range": {"min_hz": 10000, "max_hz": 20000},
+    "modulations": ["NFM", "FM"],
+    "regions": ["US"],
+    "sigidwiki_url": null
+  },
+  {
+    "id": "maritime-vhf",
+    "name": "Maritime VHF",
+    "description": "Marine VHF radio communications. Channel 16 (156.8 MHz) is the international distress and calling channel.",
+    "categories": ["maritime", "voice", "marine"],
+    "frequency_ranges": [{"min_hz": 156000000, "max_hz": 174000000}],
+    "bandwidth_range": {"min_hz": 12000, "max_hz": 25000},
+    "modulations": ["NFM", "FM"],
+    "regions": ["GLOBAL"],
+    "sigidwiki_url": "https://www.sigidwiki.com/wiki/Marine_VHF_Radio"
+  },
+  {
+    "id": "ais",
+    "name": "AIS (Automatic Identification System)",
+    "description": "Vessel tracking system transmitting position, speed, and identity data. Operates on VHF channels 87B (161.975 MHz) and 88B (162.025 MHz).",
+    "categories": ["maritime", "data", "tracking", "navigation"],
+    "frequency_ranges": [
+      {"min_hz": 161975000, "max_hz": 161975000},
+      {"min_hz": 162025000, "max_hz": 162025000}
+    ],
+    "bandwidth_range": {"min_hz": 12500, "max_hz": 25000},
+    "modulations": ["GMSK", "NFM"],
+    "regions": ["GLOBAL"],
+    "sigidwiki_url": "https://www.sigidwiki.com/wiki/Automatic_Identification_System_(AIS)"
+  },
+  {
+    "id": "noaa-weather-radio",
+    "name": "NOAA Weather Radio",
+    "description": "US National Weather Service continuous weather broadcast on 7 designated VHF channels between 162.400 and 162.550 MHz.",
+    "categories": ["broadcast", "weather", "government"],
+    "frequency_ranges": [{"min_hz": 162400000, "max_hz": 162550000}],
+    "bandwidth_range": {"min_hz": 10000, "max_hz": 20000},
+    "modulations": ["NFM", "FM"],
+    "regions": ["US"],
+    "sigidwiki_url": "https://www.sigidwiki.com/wiki/NOAA_Weather_Radio"
+  },
+  {
+    "id": "dab-digital-radio",
+    "name": "DAB Digital Radio",
+    "description": "Digital Audio Broadcasting. European digital radio standard replacing FM in many countries. Broad multiplex blocks.",
+    "categories": ["broadcast", "digital", "audio"],
+    "frequency_ranges": [
+      {"min_hz": 174928000, "max_hz": 239200000},
+      {"min_hz": 1452960000, "max_hz": 1490624000}
+    ],
+    "bandwidth_range": {"min_hz": 1536000, "max_hz": 1536000},
+    "modulations": ["OFDM"],
+    "regions": ["EU", "UK", "AU"],
+    "sigidwiki_url": "https://www.sigidwiki.com/wiki/DAB"
+  },
+  {
+    "id": "amateur-2m",
+    "name": "Amateur Radio (2m Band)",
+    "description": "2 metre amateur radio band. Used for local voice repeaters, packet radio, satellite communications, and weak signal work.",
+    "categories": ["amateur", "ham", "voice"],
+    "frequency_ranges": [{"min_hz": 144000000, "max_hz": 146000000}],
+    "bandwidth_range": {"min_hz": 10000, "max_hz": 200000},
+    "modulations": ["NFM", "FM", "USB", "LSB", "AM", "PSK"],
+    "regions": ["GLOBAL"],
+    "sigidwiki_url": null
+  },
+  {
+    "id": "amateur-70cm",
+    "name": "Amateur Radio (70cm Band)",
+    "description": "70 centimetre amateur radio band. Common for repeaters, ATV, packet radio, and digital modes.",
+    "categories": ["amateur", "ham", "voice"],
+    "frequency_ranges": [{"min_hz": 430000000, "max_hz": 440000000}],
+    "bandwidth_range": {"min_hz": 10000, "max_hz": 200000},
+    "modulations": ["NFM", "FM", "USB", "LSB", "DSTAR", "DMR", "C4FM"],
+    "regions": ["GLOBAL"],
+    "sigidwiki_url": null
+  },
+  {
+    "id": "acars",
+    "name": "ACARS (Aircraft Communications)",
+    "description": "Aircraft Communications Addressing and Reporting System. Data link for operational airline messages between aircraft and ground stations.",
+    "categories": ["aviation", "data", "aeronautical"],
+    "frequency_ranges": [
+      {"min_hz": 129125000, "max_hz": 129125000},
+      {"min_hz": 136900000, "max_hz": 136900000},
+      {"min_hz": 131725000, "max_hz": 131725000}
+    ],
+    "bandwidth_range": {"min_hz": 2400, "max_hz": 6000},
+    "modulations": ["AM", "NFM"],
+    "regions": ["GLOBAL"],
+    "sigidwiki_url": "https://www.sigidwiki.com/wiki/ACARS"
+  },
+  {
+    "id": "ads-b",
+    "name": "ADS-B (Aircraft Tracking)",
+    "description": "Automatic Dependent Surveillance-Broadcast. Aircraft transmit GPS position, altitude, and identity at 1090 MHz for air traffic control.",
+    "categories": ["aviation", "data", "tracking", "navigation"],
+    "frequency_ranges": [{"min_hz": 1090000000, "max_hz": 1090000000}],
+    "bandwidth_range": {"min_hz": 1000000, "max_hz": 2000000},
+    "modulations": ["PPM"],
+    "regions": ["GLOBAL"],
+    "sigidwiki_url": "https://www.sigidwiki.com/wiki/ADS-B"
+  },
+  {
+    "id": "pocsag",
+    "name": "POCSAG Pager",
+    "description": "Post Office Code Standardisation Advisory Group pager protocol. One-way numeric or text messaging to pagers. Common in hospitals and emergency services.",
+    "categories": ["pager", "data", "utility"],
+    "frequency_ranges": [
+      {"min_hz": 138000000, "max_hz": 175000000},
+      {"min_hz": 450000000, "max_hz": 470000000}
+    ],
+    "bandwidth_range": {"min_hz": 8000, "max_hz": 20000},
+    "modulations": ["FSK", "NFM"],
+    "regions": ["GLOBAL"],
+    "sigidwiki_url": "https://www.sigidwiki.com/wiki/POCSAG"
+  },
+  {
+    "id": "lte-700",
+    "name": "LTE / 4G (700 MHz)",
+    "description": "Long-Term Evolution mobile data network. 700 MHz band used for rural coverage and in-building penetration.",
+    "categories": ["cellular", "data", "mobile"],
+    "frequency_ranges": [{"min_hz": 698000000, "max_hz": 806000000}],
+    "bandwidth_range": {"min_hz": 1400000, "max_hz": 20000000},
+    "modulations": ["OFDM", "LTE"],
+    "regions": ["GLOBAL"],
+    "sigidwiki_url": null
+  },
+  {
+    "id": "gsm-900",
+    "name": "GSM 900 (2G Mobile)",
+    "description": "Global System for Mobile Communications on 900 MHz band. Voice calls and SMS. Being phased out but still active in many regions.",
+    "categories": ["cellular", "voice", "mobile"],
+    "frequency_ranges": [{"min_hz": 880000000, "max_hz": 960000000}],
+    "bandwidth_range": {"min_hz": 200000, "max_hz": 200000},
+    "modulations": ["GMSK"],
+    "regions": ["GLOBAL"],
+    "sigidwiki_url": "https://www.sigidwiki.com/wiki/GSM"
+  },
+  {
+    "id": "wifi-24ghz",
+    "name": "WiFi / Bluetooth (2.4 GHz ISM)",
+    "description": "IEEE 802.11 b/g/n/ax WiFi and Bluetooth Classic/BLE sharing the 2.4 GHz ISM band. 13 channels (EU) or 11 (US).",
+    "categories": ["ism", "wifi", "bluetooth", "data"],
+    "frequency_ranges": [{"min_hz": 2400000000, "max_hz": 2484000000}],
+    "bandwidth_range": {"min_hz": 1000000, "max_hz": 22000000},
+    "modulations": ["OFDM", "DSSS", "FHSS"],
+    "regions": ["GLOBAL"],
+    "sigidwiki_url": null
+  }
+]
+```
+
+- [ ] **Step 4: Run schema test — expect all tests pass**
+
+```bash
+cd /Users/admin/Dev/intercept && pytest tests/test_signals_json.py -v
+```
+
+Expected output (all pass):
+```
+tests/test_signals_json.py::TestSignalsJsonSchema::test_file_loads_as_list PASSED
+tests/test_signals_json.py::TestSignalsJsonSchema::test_all_ids_unique PASSED
+tests/test_signals_json.py::TestSignalsJsonSchema::test_required_string_fields PASSED
+tests/test_signals_json.py::TestSignalsJsonSchema::test_frequency_ranges_valid PASSED
+tests/test_signals_json.py::TestSignalsJsonSchema::test_bandwidth_range_valid_or_null PASSED
+tests/test_signals_json.py::TestSignalsJsonSchema::test_modulations_uppercase_strings PASSED
+tests/test_signals_json.py::TestSignalsJsonSchema::test_categories_list_of_strings PASSED
+tests/test_signals_json.py::TestSignalsJsonSchema::test_regions_valid_values PASSED
+tests/test_signals_json.py::TestSignalsJsonSchema::test_sigidwiki_url_string_or_null PASSED
+```
+
+Note: The AIS entry has two `frequency_ranges` where `min_hz == max_hz` (point frequencies at 161.975 and 162.025 MHz). The schema test permits `min_hz < max_hz`, so adjust those two entries to use a 1 Hz range: `{"min_hz": 161974999, "max_hz": 161975001}` and `{"min_hz": 162024999, "max_hz": 162025001}`. Same for ADS-B at 1090 MHz and ACARS point frequencies.
+
+- [ ] **Step 5: Fix point-frequency entries to use ±500 Hz ranges**
+
+Edit `data/signals.json` — replace exact point frequencies with 1 kHz windows:
+- AIS channel 87B: `{"min_hz": 161974500, "max_hz": 161975500}`
+- AIS channel 88B: `{"min_hz": 162024500, "max_hz": 162025500}`
+- ADS-B: `{"min_hz": 1089500000, "max_hz": 1090500000}`
+- ACARS 129.125: `{"min_hz": 129124500, "max_hz": 129125500}`
+- ACARS 136.900: `{"min_hz": 136899500, "max_hz": 136900500}`
+- ACARS 131.725: `{"min_hz": 131724500, "max_hz": 131725500}`
+
+Re-run tests: `pytest tests/test_signals_json.py -v` — all should pass.
+
+- [ ] **Step 6: Commit**
+
+```bash
+git add data/signals.json tests/test_signals_json.py
+git commit -m "feat: add signal database seed and schema validation test"
+```
+
+---
+
+## Task 2: Database loader + match function
+
+**Files:**
+- Create: `utils/signal_db.py`
+- Create: `tests/test_signalid_match.py`
+
+**Interfaces:**
+- Consumes: `data/signals.json` (Task 1)
+- Produces:
+  - `load_signals() -> list[dict]` — returns cached signal list
+  - `match_signals(*, frequency_mhz, bandwidth_hz=None, modulation=None, region="GLOBAL", limit=8) -> list[dict]` — returns ranked matches with `score: int` and `match_reasons: list[str]` added to each result
+
+- [ ] **Step 1: Write failing tests**
+
+Create `tests/test_signalid_match.py`:
+
+```python
+"""Unit tests for the signal database loader and match function."""
+
+from __future__ import annotations
+
+import pytest
+
+
+class TestLoadSignals:
+    def test_returns_list(self):
+        from utils.signal_db import load_signals
+        signals = load_signals()
+        assert isinstance(signals, list)
+        assert len(signals) > 0
+
+    def test_cached_on_second_call(self):
+        from utils.signal_db import load_signals
+        first = load_signals()
+        second = load_signals()
+        assert first is second  # same object — cached
+
+
+class TestMatchSignals:
+    def test_fm_broadcast_matched_at_center(self):
+        from utils.signal_db import match_signals
+        results = match_signals(frequency_mhz=98.5)
+        names = [r["name"] for r in results]
+        assert "FM Broadcast Radio" in names
+
+    def test_frequency_at_exact_range_boundary_included(self):
+        from utils.signal_db import match_signals
+        # 87.5 MHz is the lower bound of FM broadcast
+        results = match_signals(frequency_mhz=87.5)
+        names = [r["name"] for r in results]
+        assert "FM Broadcast Radio" in names
+
+    def test_frequency_just_outside_range_excluded(self):
+        from utils.signal_db import match_signals
+        # 87.499 MHz is just below FM broadcast lower bound
+        results = match_signals(frequency_mhz=87.499)
+        names = [r["name"] for r in results]
+        assert "FM Broadcast Radio" not in names
+
+    def test_no_matches_returns_empty_list(self):
+        from utils.signal_db import match_signals
+        # 5000 MHz has no signals in our database
+        results = match_signals(frequency_mhz=5000.0)
+        assert results == []
+
+    def test_results_have_score_field(self):
+        from utils.signal_db import match_signals
+        results = match_signals(frequency_mhz=98.5)
+        assert len(results) > 0
+        for r in results:
+            assert "score" in r
+            assert isinstance(r["score"], int)
+            assert 0 <= r["score"] <= 100
+
+    def test_results_have_match_reasons(self):
+        from utils.signal_db import match_signals
+        results = match_signals(frequency_mhz=98.5)
+        assert len(results) > 0
+        for r in results:
+            assert "match_reasons" in r
+            assert isinstance(r["match_reasons"], list)
+
+    def test_results_sorted_by_score_descending(self):
+        from utils.signal_db import match_signals
+        results = match_signals(frequency_mhz=98.5)
+        scores = [r["score"] for r in results]
+        assert scores == sorted(scores, reverse=True)
+
+    def test_limit_respected(self):
+        from utils.signal_db import match_signals
+        results = match_signals(frequency_mhz=98.5, limit=2)
+        assert len(results) <= 2
+
+    def test_limit_clamped_to_minimum_1(self):
+        from utils.signal_db import match_signals
+        results = match_signals(frequency_mhz=98.5, limit=0)
+        assert len(results) >= 1
+
+    def test_bandwidth_within_range_scores_higher(self):
+        from utils.signal_db import match_signals
+        # FM broadcast bandwidth_range is 150k–250k Hz; 200k is within
+        with_bw = match_signals(frequency_mhz=98.5, bandwidth_hz=200_000)
+        without_bw = match_signals(frequency_mhz=98.5)
+        fm_with = next(r for r in with_bw if r["name"] == "FM Broadcast Radio")
+        fm_without = next(r for r in without_bw if r["name"] == "FM Broadcast Radio")
+        assert fm_with["score"] >= fm_without["score"]
+
+    def test_bandwidth_outside_2x_scores_zero_for_bw_criterion(self):
+        from utils.signal_db import match_signals
+        # FM broadcast max_bw is 250k Hz; 600k is > 2× that
+        results = match_signals(frequency_mhz=98.5, bandwidth_hz=600_000)
+        fm = next((r for r in results if r["name"] == "FM Broadcast Radio"), None)
+        # FM may still appear due to frequency score, but BW reason should not be "within typical"
+        if fm:
+            assert "bandwidth: within typical" not in fm["match_reasons"]
+
+    def test_modulation_exact_match_scores_higher(self):
+        from utils.signal_db import match_signals
+        with_mod = match_signals(frequency_mhz=98.5, modulation="WFM")
+        without_mod = match_signals(frequency_mhz=98.5)
+        fm_with = next(r for r in with_mod if r["name"] == "FM Broadcast Radio")
+        fm_without = next(r for r in without_mod if r["name"] == "FM Broadcast Radio")
+        assert fm_with["score"] >= fm_without["score"]
+
+    def test_modulation_mismatch_no_mod_reason(self):
+        from utils.signal_db import match_signals
+        results = match_signals(frequency_mhz=98.5, modulation="LSB")
+        fm = next((r for r in results if r["name"] == "FM Broadcast Radio"), None)
+        if fm:
+            assert "modulation: exact match" not in fm["match_reasons"]
+
+    def test_multi_range_signal_matched_by_any_range(self):
+        from utils.signal_db import match_signals
+        # POCSAG has ranges in 138-175 MHz and 450-470 MHz
+        # 162 MHz is in the first range (maritime VHF area, but also POCSAG territory)
+        results_vhf = match_signals(frequency_mhz=155.0)
+        results_uhf = match_signals(frequency_mhz=455.0)
+        vhf_names = [r["name"] for r in results_vhf]
+        uhf_names = [r["name"] for r in results_uhf]
+        assert "POCSAG Pager" in vhf_names
+        assert "POCSAG Pager" in uhf_names
+
+    def test_region_mismatch_does_not_exclude_signal(self):
+        from utils.signal_db import match_signals
+        # PMR446 is EU/UK only; should still appear with US region but may score lower
+        results = match_signals(frequency_mhz=446.09375, region="US")
+        names = [r["name"] for r in results]
+        assert "PMR446 (Licence-Free UHF)" in names
+
+    def test_original_signal_dict_not_mutated(self):
+        from utils.signal_db import load_signals, match_signals
+        original = load_signals()
+        first_id_before = original[0]["id"]
+        match_signals(frequency_mhz=98.5, modulation="WFM")
+        assert original[0]["id"] == first_id_before  # not mutated
+        assert "score" not in original[0]  # score not added in-place
+```
+
+- [ ] **Step 2: Run tests — expect ImportError or AttributeError**
+
+```bash
+cd /Users/admin/Dev/intercept && pytest tests/test_signalid_match.py -v 2>&1 | head -20
+```
+
+Expected: `ImportError: cannot import name 'load_signals' from 'utils.signal_db'`
+
+- [ ] **Step 3: Create utils/signal_db.py**
+
+```python
+"""Signal database loader and match engine.
+
+Loads data/signals.json once at startup (lazy, cached). Provides a pure
+match_signals() function that scores candidates by frequency, bandwidth,
+modulation, and region.
+"""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+from typing import Any
+
+from utils.logging import get_logger
+
+logger = get_logger('intercept.signal_db')
+
+_DB_PATH = Path(__file__).resolve().parent.parent / "data" / "signals.json"
+_cache: list[dict[str, Any]] | None = None
+
+
+def load_signals() -> list[dict[str, Any]]:
+    """Return cached signal list, loading from JSON on first call."""
+    global _cache
+    if _cache is not None:
+        return _cache
+
+    if not _DB_PATH.exists():
+        logger.warning("signals.json not found at %s — signal matching will return no results", _DB_PATH)
+        _cache = []
+        return _cache
+
+    try:
+        with open(_DB_PATH) as f:
+            data = json.load(f)
+        if not isinstance(data, list):
+            raise ValueError("signals.json must be a JSON array")
+        _cache = data
+        logger.info("Loaded %d signals from %s", len(_cache), _DB_PATH)
+    except Exception as exc:
+        logger.error("Failed to load signals.json: %s", exc)
+        _cache = []
+
+    return _cache
+
+
+def match_signals(
+    *,
+    frequency_mhz: float,
+    bandwidth_hz: int | None = None,
+    modulation: str | None = None,
+    region: str = "GLOBAL",
+    limit: int = 8,
+) -> list[dict[str, Any]]:
+    """Return signals ranked by how well they match the given parameters.
+
+    Args:
+        frequency_mhz: Centre frequency to match (required).
+        bandwidth_hz: Observed signal bandwidth in Hz (optional — improves scoring).
+        modulation: Observed modulation token e.g. 'WFM', 'AM' (optional).
+        region: User's region code e.g. 'EU', 'US', 'GLOBAL'.
+        limit: Maximum number of results to return (clamped to 1–20).
+
+    Returns:
+        List of signal dicts (copies) sorted by score descending, each with
+        added fields: score (int 0–100), match_reasons (list[str]).
+    """
+    limit = max(1, min(limit, 20))
+    target_hz = frequency_mhz * 1_000_000
+    mod_upper = modulation.strip().upper() if modulation else None
+    region_upper = region.strip().upper() if region else "GLOBAL"
+
+    candidates: list[dict[str, Any]] = []
+    for sig in load_signals():
+        ranges = sig.get("frequency_ranges", [])
+        if not any(r["min_hz"] <= target_hz <= r["max_hz"] for r in ranges):
+            continue
+        candidates.append(sig)
+
+    scored: list[dict[str, Any]] = []
+    for sig in candidates:
+        result = dict(sig)  # shallow copy — do not mutate original
+        score = 0
+        reasons: list[str] = []
+
+        # --- Frequency centrality (10–40 pts) ---
+        ranges = sig.get("frequency_ranges", [])
+        best = min(
+            ranges,
+            key=lambda r: abs(target_hz - (r["min_hz"] + r["max_hz"]) / 2),
+        )
+        centre = (best["min_hz"] + best["max_hz"]) / 2
+        half_span = (best["max_hz"] - best["min_hz"]) / 2 or 1
+        centrality = 1.0 - min(abs(target_hz - centre) / half_span, 1.0)
+        freq_pts = int(10 + 30 * centrality)
+        score += freq_pts
+        if centrality >= 0.8:
+            reasons.append("frequency: centre of range")
+        elif centrality >= 0.4:
+            reasons.append("frequency: within range")
+        else:
+            reasons.append("frequency: edge of range")
+
+        # --- Bandwidth match (0–30 pts) ---
+        bw_range = sig.get("bandwidth_range")
+        if bandwidth_hz is not None:
+            if bw_range is None:
+                score += 10
+            elif bw_range["min_hz"] <= bandwidth_hz <= bw_range["max_hz"]:
+                score += 30
+                reasons.append("bandwidth: within typical")
+            elif (bandwidth_hz <= bw_range["max_hz"] * 2
+                  and bandwidth_hz >= bw_range["min_hz"] // 2):
+                score += 15
+                reasons.append("bandwidth: near typical")
+            # else: 0 pts, no reason added
+        else:
+            score += 15  # neutral — no bandwidth provided
+
+        # --- Modulation match (0–20 pts) ---
+        sig_mods = [m.upper() for m in sig.get("modulations", [])]
+        if mod_upper:
+            if mod_upper in sig_mods:
+                score += 20
+                reasons.append("modulation: exact match")
+            # else: 0 pts
+        else:
+            score += 10  # neutral — no modulation provided
+
+        # --- Region match (5–10 pts) ---
+        sig_regions = [r.upper() for r in sig.get("regions", [])]
+        if "GLOBAL" in sig_regions or region_upper in sig_regions:
+            score += 10
+        else:
+            score += 5
+
+        result["score"] = min(score, 100)
+        result["match_reasons"] = reasons
+        scored.append(result)
+
+    scored.sort(key=lambda s: s["score"], reverse=True)
+    return scored[:limit]
+```
+
+- [ ] **Step 4: Run tests — expect all pass**
+
+```bash
+cd /Users/admin/Dev/intercept && pytest tests/test_signalid_match.py -v
+```
+
+Expected: all 16 tests pass.
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add utils/signal_db.py tests/test_signalid_match.py
+git commit -m "feat: add signal_db loader and match_signals scoring function"
+```
+
+---
+
+## Task 3: POST /signalid/match route + REGION config
+
+**Files:**
+- Modify: `routes/signalid.py` (add route at bottom)
+- Modify: `config.py` (add REGION)
+
+**Interfaces:**
+- Consumes: `match_signals()` from `utils/signal_db` (Task 2)
+- Produces: `POST /signalid/match` returning `{status, frequency_mhz, bandwidth_hz, modulation, matches, match_count, cached}`
+
+- [ ] **Step 1: Add REGION to config.py**
+
+Open `config.py`. Find the section with other `_get_env(...)` calls (around line 410+). Add after the existing env var block — search for `HOST = _get_env(` and add below the existing settings:
+
+```python
+# Signal identification region (affects match ranking; does not filter results)
+# Valid values: GLOBAL, EU, US, UK, AU
+REGION = _get_env("REGION", "GLOBAL")
+```
+
+- [ ] **Step 2: Write a failing route test**
+
+Add to `tests/test_signal_guess_api.py` (already exists — append this class at the bottom) or create `tests/test_signalid_match_route.py`:
+
+```python
+"""Integration tests for POST /signalid/match route."""
+
+from __future__ import annotations
+
+import json
+import pytest
+
+
+@pytest.fixture
+def client():
+    from app import create_app
+    app = create_app()
+    app.config["TESTING"] = True
+    with app.test_client() as c:
+        yield c
+
+
+class TestSignalidMatchRoute:
+    def test_missing_frequency_returns_400(self, client):
+        resp = client.post(
+            "/signalid/match",
+            data=json.dumps({}),
+            content_type="application/json",
+        )
+        assert resp.status_code == 400
+
+    def test_invalid_frequency_returns_400(self, client):
+        resp = client.post(
+            "/signalid/match",
+            data=json.dumps({"frequency_mhz": -1}),
+            content_type="application/json",
+        )
+        assert resp.status_code == 400
+
+    def test_valid_request_returns_200(self, client):
+        resp = client.post(
+            "/signalid/match",
+            data=json.dumps({"frequency_mhz": 98.5}),
+            content_type="application/json",
+        )
+        assert resp.status_code == 200
+        data = resp.get_json()
+        assert data["status"] == "ok"
+        assert isinstance(data["matches"], list)
+        assert isinstance(data["match_count"], int)
+
+    def test_fm_broadcast_in_results_at_98mhz(self, client):
+        resp = client.post(
+            "/signalid/match",
+            data=json.dumps({"frequency_mhz": 98.5, "modulation": "WFM"}),
+            content_type="application/json",
+        )
+        data = resp.get_json()
+        names = [m["name"] for m in data["matches"]]
+        assert "FM Broadcast Radio" in names
+
+    def test_no_matches_returns_empty_list(self, client):
+        resp = client.post(
+            "/signalid/match",
+            data=json.dumps({"frequency_mhz": 5000.0}),
+            content_type="application/json",
+        )
+        data = resp.get_json()
+        assert data["status"] == "ok"
+        assert data["matches"] == []
+        assert data["match_count"] == 0
+
+    def test_limit_param_respected(self, client):
+        resp = client.post(
+            "/signalid/match",
+            data=json.dumps({"frequency_mhz": 98.5, "limit": 2}),
+            content_type="application/json",
+        )
+        data = resp.get_json()
+        assert len(data["matches"]) <= 2
+
+    def test_bandwidth_hz_accepted(self, client):
+        resp = client.post(
+            "/signalid/match",
+            data=json.dumps({"frequency_mhz": 98.5, "bandwidth_hz": 200000}),
+            content_type="application/json",
+        )
+        assert resp.status_code == 200
+
+    def test_cached_true_on_second_identical_request(self, client):
+        payload = json.dumps({"frequency_mhz": 98.5})
+        client.post("/signalid/match", data=payload, content_type="application/json")
+        resp2 = client.post("/signalid/match", data=payload, content_type="application/json")
+        data = resp2.get_json()
+        assert data["cached"] is True
+```
+
+- [ ] **Step 3: Run tests — expect 404 (route not yet defined)**
+
+```bash
+cd /Users/admin/Dev/intercept && pytest tests/test_signalid_match_route.py -v 2>&1 | head -30
+```
+
+Expected: tests fail with 404 responses.
+
+- [ ] **Step 4: Add POST /signalid/match to routes/signalid.py**
+
+Open `routes/signalid.py`. Add import at top of file alongside existing imports:
+
+```python
+import config
+from utils.signal_db import match_signals
+```
+
+Then append the new route at the bottom of the file (after the existing `sigidwiki_lookup` function):
+
+```python
+_match_cache: dict[str, dict[str, Any]] = {}
+
+
+@signalid_bp.route('/match', methods=['POST'])
+def signalid_match() -> Response:
+    """Match a signal by frequency, bandwidth, and modulation against the local database."""
+    payload = request.get_json(silent=True) or {}
+
+    freq_raw = payload.get('frequency_mhz')
+    if freq_raw is None:
+        return api_error('frequency_mhz is required', 400)
+    try:
+        frequency_mhz = float(freq_raw)
+    except (TypeError, ValueError):
+        return api_error('Invalid frequency_mhz', 400)
+    if frequency_mhz <= 0:
+        return api_error('frequency_mhz must be positive', 400)
+
+    bw_raw = payload.get('bandwidth_hz')
+    bandwidth_hz: int | None = None
+    if bw_raw is not None:
+        try:
+            bandwidth_hz = int(float(bw_raw))
+        except (TypeError, ValueError):
+            return api_error('Invalid bandwidth_hz', 400)
+        if bandwidth_hz <= 0:
+            return api_error('bandwidth_hz must be positive', 400)
+
+    modulation = str(payload.get('modulation') or '').strip().upper()[:16] or None
+
+    limit_raw = payload.get('limit', 8)
+    try:
+        limit = max(1, min(int(limit_raw), 20))
+    except (TypeError, ValueError):
+        limit = 8
+
+    region = getattr(config, 'REGION', 'GLOBAL')
+
+    cache_key = f'{round(frequency_mhz, 6)}|{bandwidth_hz}|{modulation}|{limit}|{region}'
+    cached = _cache_get_match(cache_key)
+    if cached is not None:
+        return jsonify({
+            'status': 'ok',
+            'frequency_mhz': round(frequency_mhz, 6),
+            'bandwidth_hz': bandwidth_hz,
+            'modulation': modulation,
+            'cached': True,
+            **cached,
+        })
+
+    try:
+        matches = match_signals(
+            frequency_mhz=frequency_mhz,
+            bandwidth_hz=bandwidth_hz,
+            modulation=modulation,
+            region=region,
+            limit=limit,
+        )
+    except Exception as exc:
+        logger.error('Signal match failed: %s', exc)
+        return api_error('Signal match failed', 502)
+
+    response_data = {
+        'matches': matches,
+        'match_count': len(matches),
+    }
+    _cache_set_match(cache_key, response_data)
+
+    return jsonify({
+        'status': 'ok',
+        'frequency_mhz': round(frequency_mhz, 6),
+        'bandwidth_hz': bandwidth_hz,
+        'modulation': modulation,
+        'cached': False,
+        **response_data,
+    })
+
+
+def _cache_get_match(key: str) -> Any | None:
+    entry = _match_cache.get(key)
+    if not entry:
+        return None
+    if time.time() >= entry['expires']:
+        _match_cache.pop(key, None)
+        return None
+    return entry['data']
+
+
+def _cache_set_match(key: str, data: Any, ttl: int = 60) -> None:
+    _match_cache[key] = {'data': data, 'expires': time.time() + ttl}
+```
+
+- [ ] **Step 5: Run route tests — expect all pass**
+
+```bash
+cd /Users/admin/Dev/intercept && pytest tests/test_signalid_match_route.py -v
+```
+
+Expected: all 8 tests pass.
+
+- [ ] **Step 6: Run full test suite to check for regressions**
+
+```bash
+cd /Users/admin/Dev/intercept && pytest tests/test_signals_json.py tests/test_signalid_match.py tests/test_signalid_match_route.py -v
+```
+
+Expected: all tests pass.
+
+- [ ] **Step 7: Commit**
+
+```bash
+git add routes/signalid.py config.py tests/test_signalid_match_route.py
+git commit -m "feat: add POST /signalid/match route with scoring and caching"
+```
+
+---
+
+## Task 4: Signal ID modal component
+
+**Files:**
+- Create: `static/js/components/signal-id-modal.js`
+- Modify: `templates/index.html` (add eager script tag)
+
+**Interfaces:**
+- Consumes: `POST /signalid/match` (Task 3)
+- Produces: `window.SignalIdModal` with `open(opts)` and `close()` methods
+  - `opts.frequency_mhz` (number, optional) — pre-fills frequency field
+  - `opts.modulation` (string, optional) — pre-selects modulation
+
+- [ ] **Step 1: Create static/js/components/signal-id-modal.js**
+
+```javascript
+/* Signal identification modal — standalone IIFE component.
+ * Usage: SignalIdModal.open({ frequency_mhz: 98.5, modulation: 'WFM' })
+ *        SignalIdModal.open({})   // blank fields
+ *        SignalIdModal.close()
+ */
+window.SignalIdModal = (function () {
+    'use strict';
+
+    var _modal = null;
+    var _backdrop = null;
+    var _lastFreq = null;
+    var _lastMod = null;
+
+    function _esc(s) {
+        return String(s == null ? '' : s)
+            .replace(/&/g, '&amp;')
+            .replace(/</g, '&lt;')
+            .replace(/>/g, '&gt;')
+            .replace(/"/g, '&quot;')
+            .replace(/'/g, '&#39;');
+    }
+
+    function _safeSigIdUrl(url) {
+        try {
+            var p = new URL(String(url || ''));
+            if (p.protocol === 'https:' && p.hostname.endsWith('sigidwiki.com')) return p.toString();
+        } catch (_) {}
+        return null;
+    }
+
+    function _build() {
+        if (_modal) return;
+
+        _backdrop = document.createElement('div');
+        _backdrop.id = 'sigIdBackdrop';
+        _backdrop.style.cssText = [
+            'position:fixed', 'inset:0', 'z-index:9998',
+            'background:rgba(0,0,0,0.65)', 'display:none',
+        ].join(';');
+        _backdrop.addEventListener('click', close);
+
+        _modal = document.createElement('div');
+        _modal.id = 'sigIdModal';
+        _modal.style.cssText = [
+            'position:fixed', 'top:50%', 'left:50%',
+            'transform:translate(-50%,-50%)',
+            'z-index:9999',
+            'width:min(500px,95vw)', 'max-height:85vh',
+            'overflow-y:auto',
+            'background:var(--bg-card,#1a1a2e)',
+            'border:1px solid rgba(255,255,255,0.12)',
+            'border-radius:8px', 'padding:16px',
+            'display:none',
+            'font-family:var(--font-mono,monospace)',
+            'color:var(--text-primary,#e0e0e0)',
+            'box-sizing:border-box',
+        ].join(';');
+
+        _modal.innerHTML = [
+            '<div style="display:flex;justify-content:space-between;align-items:center;margin-bottom:14px;">',
+            '  <div style="font-size:13px;font-weight:700;">Signal Identification</div>',
+            '  <button id="sigIdClose" style="background:none;border:none;color:var(--text-muted,#888);',
+            '    cursor:pointer;font-size:20px;line-height:1;padding:0 4px;" aria-label="Close">&times;</button>',
+            '</div>',
+            '<div style="display:grid;grid-template-columns:1fr 1fr;gap:8px;margin-bottom:8px;">',
+            '  <div>',
+            '    <label for="sigIdFreq" style="font-size:10px;color:var(--text-muted,#888);display:block;margin-bottom:3px;">',
+            '      Frequency (MHz)</label>',
+            '    <input id="sigIdFreq" type="number" step="0.0001" min="0.001" max="6000"',
+            '      style="width:100%;background:var(--bg-input,rgba(255,255,255,0.07));',
+            '      border:1px solid rgba(255,255,255,0.15);border-radius:4px;',
+            '      color:var(--text-primary,#e0e0e0);padding:5px 8px;',
+            '      font-family:var(--font-mono,monospace);font-size:11px;box-sizing:border-box;">',
+            '  </div>',
+            '  <div>',
+            '    <label for="sigIdBw" style="font-size:10px;color:var(--text-muted,#888);display:block;margin-bottom:3px;">',
+            '      Bandwidth (kHz)</label>',
+            '    <input id="sigIdBw" type="number" step="0.1" min="0.1" placeholder="optional"',
+            '      style="width:100%;background:var(--bg-input,rgba(255,255,255,0.07));',
+            '      border:1px solid rgba(255,255,255,0.15);border-radius:4px;',
+            '      color:var(--text-primary,#e0e0e0);padding:5px 8px;',
+            '      font-family:var(--font-mono,monospace);font-size:11px;box-sizing:border-box;">',
+            '  </div>',
+            '</div>',
+            '<div style="display:flex;gap:8px;margin-bottom:12px;align-items:flex-end;">',
+            '  <div style="flex:1;">',
+            '    <label for="sigIdMod" style="font-size:10px;color:var(--text-muted,#888);display:block;margin-bottom:3px;">',
+            '      Modulation</label>',
+            '    <select id="sigIdMod" style="width:100%;background:var(--bg-input,rgba(255,255,255,0.07));',
+            '      border:1px solid rgba(255,255,255,0.15);border-radius:4px;',
+            '      color:var(--text-primary,#e0e0e0);padding:5px 8px;',
+            '      font-family:var(--font-mono,monospace);font-size:11px;box-sizing:border-box;">',
+            '      <option value="">Auto</option>',
+            '      <option value="WFM">WFM</option>',
+            '      <option value="NFM">NFM</option>',
+            '      <option value="FM">FM</option>',
+            '      <option value="AM">AM</option>',
+            '      <option value="USB">USB</option>',
+            '      <option value="LSB">LSB</option>',
+            '      <option value="FSK">FSK</option>',
+            '      <option value="OOK">OOK</option>',
+            '      <option value="PSK">PSK</option>',
+            '    </select>',
+            '  </div>',
+            '  <button id="sigIdSearch" style="background:var(--accent-cyan,#00c8ff);color:#000;',
+            '    border:none;border-radius:4px;padding:6px 18px;font-size:11px;font-weight:700;',
+            '    cursor:pointer;font-family:var(--font-mono,monospace);white-space:nowrap;">',
+            '    Search</button>',
+            '</div>',
+            '<div id="sigIdStatus" style="font-size:10px;color:var(--text-muted,#888);min-height:14px;margin-bottom:8px;"></div>',
+            '<div id="sigIdResults"></div>',
+        ].join('');
+
+        document.body.appendChild(_backdrop);
+        document.body.appendChild(_modal);
+
+        document.getElementById('sigIdClose').addEventListener('click', close);
+        document.getElementById('sigIdSearch').addEventListener('click', search);
+        document.getElementById('sigIdFreq').addEventListener('input', _validateFreq);
+    }
+
+    function _validateFreq() {
+        var freq = document.getElementById('sigIdFreq');
+        var btn = document.getElementById('sigIdSearch');
+        if (!freq || !btn) return;
+        var val = parseFloat(freq.value);
+        var valid = isFinite(val) && val > 0;
+        btn.disabled = !valid;
+        freq.style.borderColor = (freq.value === '' || valid)
+            ? 'rgba(255,255,255,0.15)'
+            : 'var(--accent-red,#ff4444)';
+    }
+
+    function _setStatus(text, isError) {
+        var el = document.getElementById('sigIdStatus');
+        if (!el) return;
+        el.textContent = text || '';
+        el.style.color = isError ? 'var(--accent-red,#ff4444)' : 'var(--text-muted,#888)';
+    }
+
+    function _renderResults(matches, freqMhz) {
+        var el = document.getElementById('sigIdResults');
+        if (!el) return;
+        if (!matches.length) {
+            el.innerHTML = '<div style="font-size:10px;color:var(--text-muted,#888);">'
+                + 'No signals match ' + freqMhz.toFixed(4) + ' MHz'
+                + ' — try adjusting the frequency or leaving bandwidth blank.</div>';
+            return;
+        }
+        el.innerHTML = matches.map(function (m, i) {
+            var dot = i === 0 ? '●' : '○';
+            var score = Number(m.score) || 0;
+            var name = _esc(m.name || 'Unknown');
+            var desc = _esc(m.description || '');
+            var cats = Array.isArray(m.categories) ? m.categories : [];
+            var reasons = Array.isArray(m.match_reasons) ? m.match_reasons : [];
+            var safeUrl = _safeSigIdUrl(m.sigidwiki_url);
+            var ranges = Array.isArray(m.frequency_ranges) ? m.frequency_ranges : [];
+            var mods = Array.isArray(m.modulations) ? m.modulations : [];
+            var bw = m.bandwidth_range;
+
+            var freqStr = ranges.length
+                ? (ranges[0].min_hz / 1e6).toFixed(3) + '–' + (ranges[0].max_hz / 1e6).toFixed(3) + ' MHz'
+                : '';
+            var bwStr = bw
+                ? (bw.min_hz >= 1000 ? (bw.min_hz / 1000).toFixed(0) + 'k' : bw.min_hz)
+                  + '–'
+                  + (bw.max_hz >= 1000 ? (bw.max_hz / 1000).toFixed(0) + 'k' : bw.max_hz)
+                  + ' Hz'
+                : '';
+            var modStr = mods.join(', ');
+            var meta = [freqStr, modStr, bwStr].filter(Boolean).join(' · ');
+
+            var catHtml = cats.slice(0, 5).map(function (c) {
+                return '<span style="background:rgba(0,200,255,0.1);color:var(--accent-cyan,#00c8ff);'
+                    + 'padding:1px 5px;border-radius:3px;font-size:9px;margin-right:3px;">'
+                    + _esc(c) + '</span>';
+            }).join('');
+
+            return '<div style="border:1px solid rgba(255,255,255,0.08);border-radius:5px;'
+                + 'padding:8px;margin-bottom:6px;">'
+                + '<div style="display:flex;justify-content:space-between;align-items:flex-start;'
+                + 'gap:8px;margin-bottom:4px;">'
+                + '<div style="font-size:11px;font-weight:700;">' + dot + ' ' + name + '</div>'
+                + '<div style="display:flex;align-items:center;gap:4px;flex-shrink:0;">'
+                + '<div style="width:56px;height:5px;background:rgba(255,255,255,0.1);border-radius:3px;overflow:hidden;">'
+                + '<div style="width:' + score + '%;height:100%;background:var(--accent-cyan,#00c8ff);"></div>'
+                + '</div><div style="font-size:9px;color:var(--text-muted,#888);">' + score + '</div>'
+                + '</div></div>'
+                + (meta ? '<div style="font-size:9px;color:var(--text-muted,#888);margin-bottom:4px;">' + _esc(meta) + '</div>' : '')
+                + (desc ? '<div style="font-size:10px;color:var(--text-secondary,#b0b0b0);line-height:1.4;margin-bottom:5px;">' + desc + '</div>' : '')
+                + (catHtml ? '<div style="margin-bottom:5px;">' + catHtml + '</div>' : '')
+                + (reasons.length ? '<div style="font-size:9px;color:var(--text-dim,#666);">'
+                    + reasons.map(_esc).join(' · ') + '</div>' : '')
+                + (safeUrl ? '<div style="margin-top:5px;"><a href="' + _esc(safeUrl) + '"'
+                    + ' target="_blank" rel="noopener noreferrer"'
+                    + ' style="font-size:9px;color:var(--accent-cyan,#00c8ff);text-decoration:none;">'
+                    + '↗ View on SigID Wiki</a></div>' : '')
+                + '</div>';
+        }).join('');
+    }
+
+    function open(opts) {
+        _build();
+        opts = opts || {};
+
+        var freqEl = document.getElementById('sigIdFreq');
+        var modEl = document.getElementById('sigIdMod');
+        var bwEl = document.getElementById('sigIdBw');
+        var resultsEl = document.getElementById('sigIdResults');
+
+        if (opts.frequency_mhz != null) {
+            freqEl.value = Number(opts.frequency_mhz).toFixed(4);
+            _lastFreq = Number(opts.frequency_mhz);
+        } else {
+            freqEl.value = '';
+            _lastFreq = null;
+        }
+
+        var modVal = (opts.modulation || '').toUpperCase();
+        modEl.value = modVal || '';
+
+        bwEl.value = '';
+        resultsEl.innerHTML = '';
+        _setStatus('');
+        _validateFreq();
+
+        _backdrop.style.display = 'block';
+        _modal.style.display = 'block';
+
+        if (!opts.frequency_mhz) {
+            setTimeout(function () { freqEl.focus(); }, 50);
+        }
+    }
+
+    function close() {
+        if (!_modal) return;
+        _modal.style.display = 'none';
+        _backdrop.style.display = 'none';
+    }
+
+    function search() {
+        var freqEl = document.getElementById('sigIdFreq');
+        var modEl = document.getElementById('sigIdMod');
+        var bwEl = document.getElementById('sigIdBw');
+        var searchBtn = document.getElementById('sigIdSearch');
+
+        var freq = parseFloat(freqEl.value);
+        if (!isFinite(freq) || freq <= 0) return;
+
+        var bwKhz = parseFloat(bwEl.value);
+        var bwHz = (isFinite(bwKhz) && bwKhz > 0) ? Math.round(bwKhz * 1000) : null;
+        var mod = (modEl.value || '').trim().toUpperCase() || null;
+
+        _setStatus('Searching ' + freq.toFixed(4) + ' MHz…');
+        document.getElementById('sigIdResults').innerHTML = '';
+        searchBtn.disabled = true;
+
+        fetch('/signalid/match', {
+            method: 'POST',
+            headers: {'Content-Type': 'application/json'},
+            body: JSON.stringify({
+                frequency_mhz: freq,
+                bandwidth_hz: bwHz,
+                modulation: mod,
+                limit: 8,
+            }),
+        })
+        .then(function (r) { return r.json(); })
+        .then(function (data) {
+            searchBtn.disabled = false;
+            if (!data || data.status !== 'ok') {
+                _setStatus('Search failed', true);
+                return;
+            }
+            var matches = data.matches || [];
+            if (matches.length) {
+                _setStatus(matches.length + ' match' + (matches.length !== 1 ? 'es' : '')
+                    + ' for ' + freq.toFixed(4) + ' MHz');
+            }
+            _renderResults(matches, freq);
+        })
+        .catch(function () {
+            searchBtn.disabled = false;
+            _setStatus('Search failed — check connection', true);
+            document.getElementById('sigIdResults').innerHTML =
+                '<div style="font-size:10px;color:var(--accent-red,#ff4444);">'
+                + 'Network error — <button onclick="window.SignalIdModal.search()" '
+                + 'style="background:none;border:none;color:var(--accent-cyan,#00c8ff);'
+                + 'cursor:pointer;font-size:10px;padding:0;">Retry</button></div>';
+        });
+    }
+
+    return {open: open, close: close, search: search};
+})();
+```
+
+- [ ] **Step 2: Add eager script tag to templates/index.html**
+
+In `templates/index.html`, find the block of eagerly-loaded component scripts near the bottom (around line 3663 — the `<script src=".../js/components/signal-guess.js">` line). Add immediately after the last component script tag before the mode-scripts comment:
+
+```html
+    <script src="{{ url_for('static', filename='js/components/signal-id-modal.js') }}?v={{ version }}"></script>
+```
+
+- [ ] **Step 3: Manually verify the modal renders correctly**
+
+Start the dev server: `sudo -E venv/bin/python intercept.py`
+
+Open the browser console and run:
+```javascript
+SignalIdModal.open({ frequency_mhz: 98.5, modulation: 'WFM' })
+```
+
+Verify:
+- Modal and backdrop appear
+- Frequency field shows `98.5000`
+- Modulation shows `WFM`
+- Clicking "Search" fires a network request to `/signalid/match`
+- Results render with score bars and match reasons
+- FM Broadcast Radio appears as top result
+- Clicking × or backdrop closes the modal
+
+Then run: `SignalIdModal.open({})` and verify the frequency field is blank and focused.
+
+- [ ] **Step 4: Commit**
+
+```bash
+git add static/js/components/signal-id-modal.js templates/index.html
+git commit -m "feat: add SignalIdModal IIFE component with scored results"
+```
+
+---
+
+## Task 5: Nav button + waterfall integration
+
+**Files:**
+- Modify: `templates/partials/nav.html`
+- Modify: `templates/partials/modes/waterfall.html`
+- Modify: `static/js/modes/waterfall.js`
+
+**Interfaces:**
+- Consumes: `window.SignalIdModal.open(opts)` (Task 4)
+
+- [ ] **Step 1: Add "Signal ID" button to nav.html**
+
+In `templates/partials/nav.html`, find the Intel group `<div class="mode-nav-dropdown-menu">` (the one containing `tscm`, `spystations`, `websdr`, `drone` items — around line 150). Add a Signal ID button as the first item inside that dropdown menu:
+
+```html
+            <button type="button" class="mode-nav-btn"
+                    onclick="if(window.SignalIdModal) SignalIdModal.open({})"
+                    aria-label="Signal ID">
+                <span class="nav-icon icon"><svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><circle cx="11" cy="11" r="6"/><path d="M17 17l4 4"/><path d="M8 11h6"/><path d="M11 8v6"/></svg></span>
+                <span class="nav-label">Signal ID</span>
+            </button>
+```
+
+The SVG is a magnifying glass with a + symbol — representing "find/identify signal".
+
+- [ ] **Step 2: Replace Signal ID sidebar panel in waterfall.html**
+
+In `templates/partials/modes/waterfall.html`, find and replace the entire Signal Identification `<div class="section">` block (lines 127–154, from `<div class="section">` through `</div>` containing `wfSigIdExternal`):
+
+Replace this entire block:
+```html
+    <div class="section">
+        <h3>Signal Identification</h3>
+        <div class="wf-side-help">
+            Identify current frequency using local catalog and SigID Wiki matches.
+        </div>
+        <div class="form-group">
+            <label for="wfSigIdFreq">Frequency (MHz)</label>
+            <input type="number" id="wfSigIdFreq" value="100.0000" step="0.0001" min="0.001" max="6000">
+        </div>
+        <div class="form-group">
+            <label for="wfSigIdMode">Mode Hint</label>
+            <select id="wfSigIdMode">
+                <option value="auto" selected>Auto (Current Mode)</option>
+                <option value="wfm">WFM</option>
+                <option value="fm">NFM</option>
+                <option value="am">AM</option>
+                <option value="usb">USB</option>
+                <option value="lsb">LSB</option>
+            </select>
+        </div>
+        <div class="wf-side-grid-2">
+            <button class="preset-btn" onclick="Waterfall.useTuneForSignalId()">Use Tuned</button>
+            <button class="preset-btn" onclick="Waterfall.identifySignal()">Identify</button>
+        </div>
+        <div id="wfSigIdStatus" class="wf-side-status-line">Ready</div>
+        <div id="wfSigIdResult" class="wf-side-box" style="display:none;"></div>
+        <div id="wfSigIdExternal" class="wf-side-box wf-side-box-muted" style="display:none;"></div>
+    </div>
+```
+
+With this compact replacement:
+```html
+    <div class="section">
+        <h3>Signal Identification</h3>
+        <div class="wf-side-help">
+            Identify the current frequency against the local signal database.
+        </div>
+        <button class="preset-btn" style="width:100%;" onclick="Waterfall.openSignalId()">
+            Identify Signal
+        </button>
+    </div>
+```
+
+- [ ] **Step 3: Update waterfall.js — replace signalid handoff and add openSignalId()**
+
+In `static/js/modes/waterfall.js`, find the `handoff('signalid')` branch (around line 1438):
+
+```javascript
+            } else if (target === 'signalid') {
+                useTuneForSignalId();
+                _setHandoffStatus(`Running Signal ID at ${currentFreq.toFixed(4)} MHz`);
+                identifySignal().catch((err) => {
+                    _setSignalIdStatus(`Signal ID failed: ${err && err.message ? err.message : 'unknown error'}`, true);
+                });
+```
+
+Replace that branch with:
+
+```javascript
+            } else if (target === 'signalid') {
+                if (window.SignalIdModal) {
+                    SignalIdModal.open({ frequency_mhz: currentFreq, modulation: _getMonitorMode() });
+                }
+                _setHandoffStatus(`Opening Signal ID for ${currentFreq.toFixed(4)} MHz`);
+```
+
+Then find the public API block at the bottom of the IIFE (search for `return {` near the end of waterfall.js). Add `openSignalId` to the returned public API:
+
+Find the existing `return {` block and add `openSignalId` alongside the other exported functions:
+
+```javascript
+        openSignalId: function() {
+            if (window.SignalIdModal) {
+                SignalIdModal.open({
+                    frequency_mhz: Number.isFinite(_monitorFreqMhz) ? _monitorFreqMhz : _currentCenter(),
+                    modulation: _getMonitorMode(),
+                });
+            }
+        },
+```
+
+- [ ] **Step 4: Remove dead Signal ID functions from waterfall.js**
+
+Search `waterfall.js` for these now-unused functions and remove each one entirely:
+- `function _setSignalIdStatus(` (around line 250)
+- `function _signalIdFreqInput(` (around line 257)
+- `function _syncSignalIdFreq(` (around line 261)
+- `function _clearSignalIdPanels(` (around line 268)
+- `function _signalIdModeHint(` (around line 281)
+- `function _renderLocalSignalGuess(` (around line 288)
+- `function _renderExternalSignalMatches(` (around line 332)
+- `function useTuneForSignalId(` (around line 381)
+- `async function identifySignal(` (around line 386)
+
+Also remove `useTuneForSignalId` and `identifySignal` from the public `return {}` block if they are listed there.
+
+Also remove `_safeSigIdUrl` if it is only used by the above functions (check for any other references first with grep).
+
+- [ ] **Step 5: Verify the waterfall still works**
+
+Start the dev server and open the Waterfall mode. Verify:
+- "Identify Signal" button appears in the sidebar
+- Clicking it opens the Signal ID modal pre-populated with the current tuned frequency and modulation
+- The "Signal ID" handoff button (in the Handoff section) also opens the modal
+- Waterfall FFT continues running behind the modal
+- The rest of the waterfall (bookmarks, scan, monitor, etc.) is unaffected
+
+Also open the nav and verify the "Signal ID" button appears in the Intel dropdown and opens the modal with blank fields.
+
+- [ ] **Step 6: Run full test suite**
+
+```bash
+cd /Users/admin/Dev/intercept && pytest tests/test_signals_json.py tests/test_signalid_match.py tests/test_signalid_match_route.py -v
+```
+
+Expected: all tests pass with no regressions.
+
+- [ ] **Step 7: Commit**
+
+```bash
+git add templates/partials/nav.html templates/partials/modes/waterfall.html static/js/modes/waterfall.js
+git commit -m "feat: wire SignalIdModal to waterfall and global nav"
+```
+
+---
+
+## Self-Review Checklist
+
+**Spec coverage:**
+- ✅ Bundled JSON database (`data/signals.json`) — Task 1
+- ✅ Schema validation test (`tests/test_signals_json.py`) — Task 1
+- ✅ Database loader (`utils/signal_db.py`) — Task 2
+- ✅ 4-criterion scoring (frequency, bandwidth, modulation, region) — Task 2
+- ✅ match_reasons in response — Task 2
+- ✅ `POST /signalid/match` route — Task 3
+- ✅ REGION config (`INTERCEPT_REGION`) — Task 3
+- ✅ 60-second result cache — Task 3
+- ✅ Modal IIFE component (`signal-id-modal.js`) — Task 4
+- ✅ Pre-populated from waterfall (frequency + modulation) — Task 5
+- ✅ Blank entry from global nav — Task 5
+- ✅ Optional bandwidth field in modal — Task 4
+- ✅ Score bar + match reasons in modal — Task 4
+- ✅ SigID Wiki link when url present — Task 4
+- ✅ Error states (no matches, network failure, invalid freq) — Task 4
+- ✅ Waterfall continues running behind modal — by design (modal is overlay)
+- ✅ Existing `/signalid/sigidwiki` route untouched — nothing removed from it
+- ✅ `signal_guess.py` untouched — Task 3 imports `match_signals`, not replacing the old module
+
+**Type consistency:**
+- `match_signals()` is defined in Task 2 and imported in Task 3 — same signature used throughout
+- `SignalIdModal.open(opts)` defined in Task 4, called in Task 5 — consistent
+- `bandwidth_hz` is always integer Hz in Python, converted from kHz in JS before the API call