Add .claude/settings.local.json to .gitignore

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -1,2 +1,4 @@
 /.env
+/ssh_config
+.claude/settings.local.json
 

Dockerfile

@@ -17,7 +17,6 @@ RUN apt-get update -y && \
     rm -rf /var/lib/apt/lists/*
 
 ENV COLORTERM=truecolor
-ENV TERM=xterm-256color
 
 # Install Openspec
 RUN npm i -g @fission-ai/openspec@latest

LICENSE

@@ -0,0 +1,85 @@
+GNU GENERAL PUBLIC LICENSE
+
+Version 2, June 1991
+
+Copyright (C) 1989, 1991 Free Software Foundation, Inc.
+<https://fsf.org/>
+Everyone is permitted to copy and distribute verbatim copies
+of this license document, but changing it is not allowed.
+Preamble
+
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+
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+NO WARRANTY
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+11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
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+
+END OF TERMS AND CONDITIONS

README.md

@@ -0,0 +1,30 @@
+# SDR Scanner & Recorder
+
+Monitors and records EU CB radio transmissions using an RTL-SDR dongle on a Raspberry Pi 400, powered by [RTLSDR-Airband](https://github.com/charlie-foxtrot/RTLSDR-Airband).
+
+## Monitored Channels
+
+| Channel | Frequency |
+|---------|-----------|
+| CB 3    | 26.985 MHz |
+| CB 7    | 27.035 MHz |
+| CB 10   | 27.075 MHz |
+| CB 16   | 27.155 MHz |
+
+## Architecture
+
+Three Docker containers via `docker-compose`:
+
+- **rtlsdr-airband** — multichannel SDR receiver, splits recordings per-transmission into dated directories
+- **nginx** — web UI for browsing recordings on port 8080
+- **cleanup** — periodically removes short/noise recordings (< 3KB)
+
+## Usage
+
+```sh
+ssh m@sdr-pi
+cd /workspace
+docker compose up -d
+```
+
+Recordings are saved to `~/recordings/` and browsable at `http://sdr-pi:8080`.	

cleanup-recordings.sh

@@ -0,0 +1,16 @@
+#!/bin/sh
+# Deletes small MP3 recordings that are likely noise/false positives.
+# Runs in a loop, intended for use inside a Docker container.
+#
+# Environment variables:
+#   SIZE_THRESHOLD  - find -size format, e.g. 3k, 5k, 10k (default: 3k)
+#   INTERVAL        - seconds between runs (default: 300)
+
+RECORDINGS_DIR="/recordings"
+SIZE_THRESHOLD="${SIZE_THRESHOLD:-3k}"
+INTERVAL="${INTERVAL:-300}"
+
+while true; do
+  find "$RECORDINGS_DIR" -type f -name '*.mp3' -size "-${SIZE_THRESHOLD}" -mmin +1 -delete
+  sleep "$INTERVAL"
+done

docker-compose.yml

@@ -8,3 +8,25 @@ services:
     volumes:
       - ./rtl_airband.conf:/app/rtl_airband.conf:ro
       - /home/m/recordings:/recordings
+
+  web:
+    image: nginx:alpine
+    container_name: sdr-web
+    restart: unless-stopped
+    ports:
+      - "8080:80"
+    volumes:
+      - ./nginx.conf:/etc/nginx/conf.d/default.conf:ro
+      - /home/m/recordings:/recordings:ro
+
+  cleanup:
+    image: alpine:latest
+    container_name: sdr-cleanup
+    restart: unless-stopped
+    environment:
+      - SIZE_THRESHOLD=3k
+      - INTERVAL=300
+    volumes:
+      - ./cleanup-recordings.sh:/cleanup-recordings.sh:ro
+      - /home/m/recordings:/recordings
+    command: ["/bin/sh", "/cleanup-recordings.sh"]

nginx.conf

@@ -0,0 +1,8 @@
+server {
+    listen 80;
+
+    location / {
+        alias /recordings/;
+        autoindex on;
+    }
+}

openspec/changes/archive/2026-03-19-improved-false-positive-detection/.openspec.yaml

@@ -0,0 +1,2 @@
+schema: spec-driven
+created: 2026-03-19

openspec/changes/archive/2026-03-19-improved-false-positive-detection/design.md

@@ -0,0 +1,46 @@
+## Context
+
+RTLSDR-Airband monitors 3 CB channels (26.985, 27.035, 27.075 MHz) via a single RTL-SDR dongle on a Pi 400. Recordings split per transmission produce many false positives — short noise-triggered files, often on multiple channels simultaneously.
+
+Current config: `fft_size` commented out (defaults to 512), no `squelch_snr_threshold` set (defaults to 9.54 dB). Both contribute to over-sensitivity.
+
+## Goals / Non-Goals
+
+**Goals:**
+- Reduce false-positive recordings caused by noise, static, and weak signals
+- Achieve this through RTLSDR-Airband config tuning only — no post-processing
+
+**Non-Goals:**
+- Eliminating 100% of false positives (some noise will always slip through)
+- Automated cleanup scripts or post-processing pipelines
+- Changes to gain, bandwidth, or sample rate (these are working adequately)
+
+## Decisions
+
+### 1. Set `fft_size = 2048`
+
+**Decision**: Uncomment and increase `fft_size` from the current default of 512 to 2048.
+
+**Rationale**: With 3 NFM channels spaced 10 kHz apart using 8 kHz bandwidth, a 512-point FFT produces bins too wide for clean separation. This causes energy from one channel (or wideband noise) to bleed into adjacent channels, triggering simultaneous false recordings. The simultaneous cross-channel triggers observed in the recordings confirm this.
+
+2048 provides 4x the spectral resolution. Going to 4096 would be even better but may stress the Pi 400's CPU; 2048 is a safe starting point.
+
+**Alternatives considered**:
+- **4096**: Best selectivity but higher CPU cost. Can try later if 2048 isn't sufficient.
+- **1024** (the previously commented-out value): Moderate improvement but may not fully resolve cross-channel bleed.
+
+### 2. Add `squelch_snr_threshold = 15.0` per channel
+
+**Decision**: Set an explicit SNR threshold of 15 dB on each channel.
+
+**Rationale**: The default 9.54 dB is calibrated for aviation AM monitoring where signals are cleaner. CB at 27 MHz has a higher noise floor and more atmospheric interference. 15 dB is a reasonable starting point that should reject most noise while still capturing normal-strength CB transmissions.
+
+**Alternatives considered**:
+- **20-25 dB**: More aggressive, but risks missing weaker legitimate transmissions. Can increase later if 15 isn't enough.
+- **`squelch_threshold` (absolute dBFS)**: Harder to tune and doesn't adapt to changing noise floor conditions. The SNR-relative approach is more robust.
+
+## Risks / Trade-offs
+
+- **[Weak signals missed]** → Higher squelch threshold will drop marginal transmissions. Acceptable trade-off — false positives are currently more disruptive than missed weak signals.
+- **[CPU increase from larger FFT]** → 2048 uses more CPU than 512. Pi 400 quad-core should handle this comfortably, but worth monitoring after deployment.
+- **[Iterative tuning needed]** → These values are starting points. May need adjustment after observing results over a day or two.

openspec/changes/archive/2026-03-19-improved-false-positive-detection/proposal.md

@@ -0,0 +1,24 @@
+## Why
+
+The recorder generates many short false-positive recordings (360 bytes to ~4KB) triggered by noise, static, or weak signals. Multiple channels often fire simultaneously, suggesting wideband interference or poor channel isolation. The current config uses the default FFT size (512) and default squelch SNR threshold (9.54 dB), both of which are too permissive for noisy CB monitoring at 27 MHz.
+
+## What Changes
+
+- Increase `fft_size` to improve channel selectivity and reduce adjacent-channel false triggers
+- Add `squelch_snr_threshold` per channel to raise the signal-to-noise requirement for squelch opening
+- Uncomment and update the `fft_size` setting (currently commented out at 1024, defaulting to 512)
+
+## Capabilities
+
+### New Capabilities
+- `false-positive-reduction`: RTLSDR-Airband configuration tuning to minimize noise-triggered recordings via FFT size and squelch SNR threshold adjustments
+
+### Modified Capabilities
+
+_(none)_
+
+## Impact
+
+- **Configuration**: Changes to `rtl_airband.conf` only — no new services or code
+- **Pi resources**: Higher `fft_size` increases CPU usage slightly; monitor after deployment
+- **Recording behavior**: Fewer but higher-confidence recordings; very weak legitimate signals may be missed

openspec/changes/archive/2026-03-19-improved-false-positive-detection/specs/false-positive-reduction/spec.md

@@ -0,0 +1,19 @@
+## ADDED Requirements
+
+### Requirement: FFT size configured for NFM channel isolation
+The system SHALL use an `fft_size` of 2048 or greater to provide sufficient spectral resolution for separating NFM channels spaced 10 kHz apart.
+
+#### Scenario: FFT size set in config
+- **WHEN** the RTLSDR-Airband configuration is loaded
+- **THEN** the `fft_size` is set to 2048
+
+### Requirement: Squelch SNR threshold configured per channel
+Each monitored channel SHALL have a `squelch_snr_threshold` set to reduce false triggers from noise and weak signals.
+
+#### Scenario: Squelch threshold applied
+- **WHEN** a signal is detected on a monitored channel
+- **THEN** the squelch only opens if the signal exceeds the configured SNR threshold (starting value: 15.0 dB)
+
+#### Scenario: Noise below threshold is rejected
+- **WHEN** noise or interference is present but below the SNR threshold
+- **THEN** no recording is triggered

openspec/changes/archive/2026-03-19-improved-false-positive-detection/tasks.md

@@ -0,0 +1,10 @@
+## 1. Configuration Changes
+
+- [x] 1.1 Set `fft_size = 2048` in `rtl_airband.conf` (uncomment and update from 1024)
+- [x] 1.2 Add `squelch_snr_threshold = 15.0` to each of the 3 channel blocks
+
+## 2. Deploy and Verify
+
+- [x] 2.1 Copy updated config to Pi and restart the `sdr-recorder` container
+- [x] 2.2 Clear existing false-positive recordings so results are easy to evaluate
+- [x] 2.3 Observe recording behavior — confirm fewer/no short noise-triggered files appearing

openspec/changes/archive/2026-03-19-web-hosting-recordings/.openspec.yaml

@@ -0,0 +1,2 @@
+schema: spec-driven
+created: 2026-03-19

openspec/changes/archive/2026-03-19-web-hosting-recordings/design.md

@@ -0,0 +1,34 @@
+## Context
+
+RTLSDR-Airband records CB transmissions as MP3 files into `/home/m/recordings/` on the Pi, organized by channel subdirectories with dated subdirectories inside. The recorder runs as a Docker container via `docker-compose.yml`.
+
+## Goals / Non-Goals
+
+**Goals:**
+- Serve the recordings directory over HTTP with browsable directory listings
+- Allow MP3 playback via the browser's native audio handling
+- Deploy as a Docker container alongside the existing `sdr-recorder` service
+
+**Non-Goals:**
+- Custom web UI, styling, or JavaScript
+- Authentication (local network only)
+- Modifying, uploading, or deleting recordings
+- Live streaming or transcription
+
+## Decisions
+
+### Use Nginx with HTML autoindex, no custom frontend
+
+**Decision**: Use `nginx:alpine` with `autoindex on` to serve the recordings directory. No custom HTML, JS, or CSS.
+
+**Rationale**: Nginx's built-in directory listing is fully functional for browsing channel/date directories. Modern browsers play MP3 files natively when clicked. This requires only an Nginx config file and a docker-compose service — zero application code.
+
+**Alternatives considered**:
+- **Custom SPA frontend**: Adds complexity (build tools, JS code) for marginal UX improvement over native directory listing.
+- **Python http.server**: Simpler but less performant and no Alpine image parity.
+
+## Risks / Trade-offs
+
+- **[No search or filtering]** → Users browse by directory structure. Acceptable given the channel/date organization.
+- **[Plain directory listing]** → No styled UI. Acceptable for a local utility tool.
+- **[No auth]** → Anyone on the LAN can access. Acceptable per non-goals.

openspec/changes/archive/2026-03-19-web-hosting-recordings/proposal.md

@@ -0,0 +1,23 @@
+## Why
+
+Recordings from the RTLSDR-Airband CB scanner are stored as MP3 files on the Pi's filesystem (`/home/m/recordings/`), organized by channel and date. There's currently no way to browse or listen to them without SSH access. A web server with directory listing would make recordings browsable and playable from any device on the local network.
+
+## What Changes
+
+- Add an Nginx container to `docker-compose.yml` that serves the recordings directory with autoindex enabled
+- Users browse directories and click MP3 files to play them natively in the browser
+
+## Capabilities
+
+### New Capabilities
+- `recording-browser`: Nginx autoindex serving the recordings directory over HTTP, with browser-native MP3 playback
+
+### Modified Capabilities
+
+_(none)_
+
+## Impact
+
+- **Docker deployment**: New Nginx service added to `docker-compose.yml`, sharing the `/home/m/recordings` volume (read-only)
+- **Pi resources**: Negligible — Nginx Alpine uses ~2MB RAM
+- **Network**: Exposes HTTP port on the Pi's local network

openspec/changes/archive/2026-03-19-web-hosting-recordings/specs/recording-browser/spec.md

@@ -0,0 +1,34 @@
+## ADDED Requirements
+
+### Requirement: Serve recordings directory over HTTP
+The system SHALL serve the contents of the recordings directory via an Nginx web server with directory listing enabled.
+
+#### Scenario: Browse channel directories
+- **WHEN** a user navigates to the root URL of the web server
+- **THEN** the server displays a directory listing showing the channel subdirectories
+
+#### Scenario: Browse date directories within a channel
+- **WHEN** a user clicks a channel directory
+- **THEN** the server displays a directory listing of date subdirectories for that channel
+
+#### Scenario: Browse recording files within a date
+- **WHEN** a user clicks a date directory
+- **THEN** the server displays a listing of MP3 recording files
+
+### Requirement: Browser-native MP3 playback
+The system SHALL serve MP3 files with correct MIME type so browsers can play them natively.
+
+#### Scenario: Play a recording
+- **WHEN** a user clicks an MP3 file link in the directory listing
+- **THEN** the browser opens and plays the MP3 file using its native audio player
+
+### Requirement: Docker deployment
+The web server SHALL run as a Docker container defined in `docker-compose.yml`, mounting the recordings directory read-only.
+
+#### Scenario: Start alongside recorder
+- **WHEN** a user runs `docker compose up` on the Pi
+- **THEN** the Nginx service starts alongside the `sdr-recorder` service and is accessible via HTTP
+
+#### Scenario: Read-only access to recordings
+- **WHEN** the Nginx container accesses the recordings volume
+- **THEN** the volume is mounted read-only, preventing modification of recording files

openspec/changes/archive/2026-03-19-web-hosting-recordings/tasks.md

@@ -0,0 +1,11 @@
+## 1. Nginx Configuration
+
+- [x] 1.1 Create `nginx.conf` with a server block that serves `/recordings` with `autoindex on` and correct MIME type for MP3 files
+
+## 2. Docker Integration
+
+- [x] 2.1 Add an `nginx` service to `docker-compose.yml` using `nginx:alpine`, mounting `/home/m/recordings` to `/recordings:ro` and `./nginx.conf` to the Nginx config path, exposing port 8080
+
+## 3. Deploy and Verify
+
+- [x] 3.1 Deploy to the Pi and verify directory browsing and MP3 playback work at `http://sdr-pi:8080`

openspec/changes/archive/2026-03-21-add-cb-channel-16/.openspec.yaml

@@ -0,0 +1,2 @@
+schema: spec-driven
+created: 2026-03-21

openspec/changes/archive/2026-03-21-add-cb-channel-16/design.md

@@ -0,0 +1,28 @@
+## Context
+
+The system monitors CB radio channels using RTLSDR-Airband running in Docker on a Pi 400. The SDR is tuned to a center frequency of 27.035 MHz with a 2.4 MHz sample rate, covering approximately 25.835–28.235 MHz. Three channels are currently monitored (3, 7, 10). CB channel 16 at 27.155 MHz falls well within this window.
+
+## Goals / Non-Goals
+
+**Goals:**
+- Add CB channel 16 (27.155 MHz) to the monitored channel list
+- Use identical recording and squelch settings as existing channels for consistency
+
+**Non-Goals:**
+- Changing center frequency, sample rate, or gain settings
+- Adding any other channels beyond channel 16
+- Modifying the cleanup, web, or Docker configuration
+
+## Decisions
+
+**Use identical channel parameters as existing channels.**
+All current channels use 8 kHz bandwidth, NFM modulation, 9.0 dB squelch SNR threshold, and file output with split-on-transmission. Channel 16 will use the same settings. There's no reason to deviate — CB channels have uniform characteristics.
+
+**Filename template follows existing convention: `CB_CH16_27155`.**
+This matches the `CB_CH{nn}_{freq}` pattern used by channels 3, 7, and 10, keeping recordings consistent for the cleanup script and web browser.
+
+## Risks / Trade-offs
+
+**Additional CPU load from fourth channel** → Minimal risk. RTLSDR-Airband's multichannel mode handles many channels efficiently within a single FFT pass. One more channel adds negligible overhead on the Pi 400.
+
+**More recordings consuming disk space** → Mitigated by the existing cleanup container which removes files under the 3k size threshold.

openspec/changes/archive/2026-03-21-add-cb-channel-16/proposal.md

@@ -0,0 +1,24 @@
+## Why
+
+CB channel 16 (27.155 MHz) is commonly used for regional traffic and is worth monitoring alongside the existing channels 3, 7, and 10. The frequency already falls within the current SDR sample window, so adding it requires only a configuration change.
+
+## What Changes
+
+- Add CB channel 16 (27.155 MHz) as a new monitored channel in `rtl_airband.conf`
+- Uses the same NFM modulation, bandwidth, squelch, and file output settings as existing channels
+- Recordings saved with `CB_CH16_27155` filename template
+
+## Capabilities
+
+### New Capabilities
+- `cb-channel-16-monitoring`: Monitor and record transmissions on CB channel 16 (27.155 MHz)
+
+### Modified Capabilities
+
+_(none — existing channel monitoring is unchanged)_
+
+## Impact
+
+- `rtl_airband.conf`: New channel entry added to the existing device's channel list
+- No changes to Docker, Nginx, or cleanup configuration needed
+- No additional hardware or SDR tuning changes required (27.155 MHz is within the current 2.4 MHz sample window)

openspec/changes/archive/2026-03-21-add-cb-channel-16/specs/cb-channel-16-monitoring/spec.md

@@ -0,0 +1,19 @@
+## ADDED Requirements
+
+### Requirement: Monitor CB channel 16
+The system SHALL monitor CB channel 16 at 27.155 MHz using narrowband FM demodulation with an 8 kHz bandwidth and a squelch SNR threshold of 9.0 dB.
+
+#### Scenario: Channel 16 transmission detected
+- **WHEN** a transmission occurs on 27.155 MHz above the squelch threshold
+- **THEN** the system records the transmission to a file in the `/recordings` directory using dated subdirectories and the filename template `CB_CH16_27155`
+
+#### Scenario: Channel 16 transmission ends
+- **WHEN** the signal on 27.155 MHz drops below the squelch threshold
+- **THEN** the system splits the recording file at the transmission boundary
+
+### Requirement: Channel 16 labeled in configuration
+The channel entry SHALL use the label `CB-CH16` for identification in logs and status output.
+
+#### Scenario: Channel label appears in config
+- **WHEN** RTLSDR-Airband loads the configuration
+- **THEN** channel 16 is identified with the label `CB-CH16`

openspec/changes/archive/2026-03-21-add-cb-channel-16/tasks.md

@@ -0,0 +1,8 @@
+## 1. Configuration
+
+- [x] 1.1 Add CB channel 16 entry to `rtl_airband.conf` with freq 27.155, 8 kHz bandwidth, NFM modulation, 9.0 dB squelch SNR threshold, label `CB-CH16`, and file output with template `CB_CH16_27155`
+- [x] 1.2 Update the comment at the top of `rtl_airband.conf` to include channel 16
+
+## 2. Deploy
+
+- [x] 2.1 Rebuild and restart the `sdr-recorder` container on the Pi to pick up the new configuration

openspec/changes/archive/2026-03-21-recording-cleanup-cron/.openspec.yaml

@@ -0,0 +1,2 @@
+schema: spec-driven
+created: 2026-03-21

openspec/changes/archive/2026-03-21-recording-cleanup-cron/design.md

@@ -0,0 +1,42 @@
+## Context
+
+The SDR recorder running in Docker on `sdr-pi` writes MP3 files to `/home/m/recordings/` (mounted from the host). Despite squelch tuning, many files are noise — today's data shows 91 files totaling 476 KB, with the majority under 2 KB. These clutter the Nginx web browser and Samba share, making it hard to find real transmissions.
+
+The recorder container runs as root (required for USB/SDR hardware access) and writes files owned by root, so cleanup must also run as root.
+
+## Goals / Non-Goals
+
+**Goals:**
+- Automatically remove recordings that are too small to contain real audio
+- Make the size threshold easily adjustable via environment variable
+- Keep everything version-controlled in docker-compose
+- Run frequently enough that the web/Samba views stay clean
+
+**Non-Goals:**
+- Duration-based or content-based analysis (too complex, needs extra tools)
+- Age-based retention policy (handled manually for now)
+
+## Decisions
+
+### Dedicated cleanup container in docker-compose
+Add a lightweight Alpine container (`sdr-cleanup`) to docker-compose that shares the `/home/m/recordings` volume. This follows Docker's separation-of-concerns model — one container per responsibility. The container runs a simple `find -delete` loop with `sleep` instead of requiring a cron daemon. Since it runs as root (Alpine default), it can delete the root-owned files written by the recorder.
+
+Alternatives considered:
+- **Host crontab**: Simplest, but files are root-owned so needs `sudo crontab`, and isn't version-controlled in docker-compose
+- **Cron inside recorder container**: Not our image, would need custom build
+- **Systemd timer on host**: More ceremony than cron for the same result
+
+### File size threshold as the filter heuristic
+Use file size (default 3 KB) rather than MP3 duration. This avoids needing `ffprobe` or similar tools. From today's data, files under 3 KB are consistently noise — real transmissions start around 5 KB. Configurable via `SIZE_THRESHOLD` environment variable in docker-compose.
+
+### 5-minute sleep loop
+Run every 5 minutes via `sleep 300` in a loop. Lightweight and keeps the browsing experience clean.
+
+### Only delete files older than 1 minute
+Add a minimum age filter (`-mmin +1`) to avoid deleting files still being written by rtl_airband.
+
+## Risks / Trade-offs
+
+- **Threshold too aggressive** → Real short transmissions deleted. Mitigation: start conservative at 3 KB, tune via environment variable.
+- **Race condition with active writes** → The `-mmin +1` guard ensures we never delete a file rtl_airband is still writing.
+- **Container restart** → If the cleanup container crashes, `restart: unless-stopped` brings it back. No state to lose.

openspec/changes/archive/2026-03-21-recording-cleanup-cron/proposal.md

@@ -0,0 +1,25 @@
+## Why
+
+Despite tuning squelch thresholds and FFT settings, the SDR recorder still produces many small files triggered by noise rather than real CB transmissions. These clutter the web browser and Samba share, making it tedious to find actual recordings. A periodic cleanup job will automatically remove files that are too small to contain meaningful audio.
+
+## What Changes
+
+- Add a cleanup shell script that deletes MP3 files below a configurable size threshold (default: 3 KB)
+- Install a cron job on the Pi host that runs the script frequently (every 5 minutes)
+- The script and cron entry are version-controlled in this repo for documentation and tunability
+
+## Capabilities
+
+### New Capabilities
+- `recording-cleanup`: Automated periodic deletion of recordings below a configurable file-size threshold
+
+### Modified Capabilities
+
+None.
+
+## Impact
+
+- New file: cleanup script in the repo, deployed to the Pi host
+- Host crontab on `sdr-pi` will be modified to schedule the job
+- Recordings directory (`/home/m/recordings/`) will have small files automatically removed
+- No container or docker-compose changes required — this runs directly on the host

openspec/changes/archive/2026-03-21-recording-cleanup-cron/specs/recording-cleanup/spec.md

@@ -0,0 +1,37 @@
+## ADDED Requirements
+
+### Requirement: Cleanup script removes small recordings
+The system SHALL provide a shell script that deletes MP3 files below a configurable size threshold from the recordings directory. The default threshold SHALL be 3 KB (3072 bytes).
+
+#### Scenario: File below threshold is deleted
+- **WHEN** a `.mp3` file in `/home/m/recordings/` is smaller than the configured size threshold and older than 1 minute
+- **THEN** the file is deleted
+
+#### Scenario: File above threshold is preserved
+- **WHEN** a `.mp3` file in `/home/m/recordings/` is equal to or larger than the configured size threshold
+- **THEN** the file is not deleted
+
+#### Scenario: File currently being written is preserved
+- **WHEN** a `.mp3` file in `/home/m/recordings/` was modified less than 1 minute ago
+- **THEN** the file is not deleted, regardless of size
+
+### Requirement: Cleanup runs on a schedule
+The system SHALL execute the cleanup script via a cron job on the Pi host, running every 5 minutes.
+
+#### Scenario: Periodic execution
+- **WHEN** 5 minutes have elapsed since the last run
+- **THEN** the cleanup script executes and removes qualifying files
+
+### Requirement: Size threshold is configurable
+The cleanup script SHALL accept the size threshold as a parameter, allowing adjustment without editing the script.
+
+#### Scenario: Custom threshold
+- **WHEN** the script is invoked with a size argument (e.g., `5k`)
+- **THEN** only files below that size are deleted instead of the default 3 KB
+
+### Requirement: Cleanup script is version-controlled
+The cleanup script SHALL be stored in the project repository so that changes are tracked and deployable.
+
+#### Scenario: Script lives in repo
+- **WHEN** a developer checks the repository
+- **THEN** the cleanup script is present at a well-known path with documentation of its purpose

openspec/changes/archive/2026-03-21-recording-cleanup-cron/tasks.md

@@ -0,0 +1,18 @@
+## 1. Cleanup Script
+
+- [x] 1.1 Create `cleanup-recordings.sh` in the repo with configurable size threshold (default 3k), `-mmin +1` safety guard, targeting `/recordings`
+- [x] 1.2 Make the script executable and add a usage comment at the top
+
+## 2. Docker Compose
+
+- [x] 2.1 Update `cleanup-recordings.sh` to run as a loop with sleep instead of one-shot, read threshold from `SIZE_THRESHOLD` env var
+- [x] 2.2 Add `sdr-cleanup` service to `docker-compose.yml` using `alpine` image, mounting the recordings volume and running the script
+
+## 3. Deployment Cleanup
+
+- [x] 3.1 Remove the host crontab entry installed earlier on `sdr-pi`
+- [x] 3.2 Remove the script copy from `/home/m/cleanup-recordings.sh` on `sdr-pi`
+
+## 4. Verification
+
+- [x] 4.1 Deploy updated docker-compose to `sdr-pi` and confirm the cleanup container starts and deletes small files

openspec/specs/cb-channel-16-monitoring/spec.md

@@ -0,0 +1,17 @@
+### Requirement: Monitor CB channel 16
+The system SHALL monitor CB channel 16 at 27.155 MHz using narrowband FM demodulation with an 8 kHz bandwidth and a squelch SNR threshold of 9.0 dB.
+
+#### Scenario: Channel 16 transmission detected
+- **WHEN** a transmission occurs on 27.155 MHz above the squelch threshold
+- **THEN** the system records the transmission to a file in the `/recordings` directory using dated subdirectories and the filename template `CB_CH16_27155`
+
+#### Scenario: Channel 16 transmission ends
+- **WHEN** the signal on 27.155 MHz drops below the squelch threshold
+- **THEN** the system splits the recording file at the transmission boundary
+
+### Requirement: Channel 16 labeled in configuration
+The channel entry SHALL use the label `CB-CH16` for identification in logs and status output.
+
+#### Scenario: Channel label appears in config
+- **WHEN** RTLSDR-Airband loads the configuration
+- **THEN** channel 16 is identified with the label `CB-CH16`

openspec/specs/false-positive-reduction/spec.md

@@ -0,0 +1,17 @@
+### Requirement: FFT size configured for NFM channel isolation
+The system SHALL use an `fft_size` of 2048 or greater to provide sufficient spectral resolution for separating NFM channels spaced 10 kHz apart.
+
+#### Scenario: FFT size set in config
+- **WHEN** the RTLSDR-Airband configuration is loaded
+- **THEN** the `fft_size` is set to 2048
+
+### Requirement: Squelch SNR threshold configured per channel
+Each monitored channel SHALL have a `squelch_snr_threshold` set to reduce false triggers from noise and weak signals.
+
+#### Scenario: Squelch threshold applied
+- **WHEN** a signal is detected on a monitored channel
+- **THEN** the squelch only opens if the signal exceeds the configured SNR threshold (starting value: 15.0 dB)
+
+#### Scenario: Noise below threshold is rejected
+- **WHEN** noise or interference is present but below the SNR threshold
+- **THEN** no recording is triggered

openspec/specs/recording-browser/spec.md

@@ -0,0 +1,32 @@
+### Requirement: Serve recordings directory over HTTP
+The system SHALL serve the contents of the recordings directory via an Nginx web server with directory listing enabled.
+
+#### Scenario: Browse channel directories
+- **WHEN** a user navigates to the root URL of the web server
+- **THEN** the server displays a directory listing showing the channel subdirectories
+
+#### Scenario: Browse date directories within a channel
+- **WHEN** a user clicks a channel directory
+- **THEN** the server displays a directory listing of date subdirectories for that channel
+
+#### Scenario: Browse recording files within a date
+- **WHEN** a user clicks a date directory
+- **THEN** the server displays a listing of MP3 recording files
+
+### Requirement: Browser-native MP3 playback
+The system SHALL serve MP3 files with correct MIME type so browsers can play them natively.
+
+#### Scenario: Play a recording
+- **WHEN** a user clicks an MP3 file link in the directory listing
+- **THEN** the browser opens and plays the MP3 file using its native audio player
+
+### Requirement: Docker deployment
+The web server SHALL run as a Docker container defined in `docker-compose.yml`, mounting the recordings directory read-only.
+
+#### Scenario: Start alongside recorder
+- **WHEN** a user runs `docker compose up` on the Pi
+- **THEN** the Nginx service starts alongside the `sdr-recorder` service and is accessible via HTTP
+
+#### Scenario: Read-only access to recordings
+- **WHEN** the Nginx container accesses the recordings volume
+- **THEN** the volume is mounted read-only, preventing modification of recording files

openspec/specs/recording-cleanup/spec.md

@@ -0,0 +1,35 @@
+### Requirement: Cleanup script removes small recordings
+The system SHALL provide a shell script that deletes MP3 files below a configurable size threshold from the recordings directory. The default threshold SHALL be 3 KB (3072 bytes).
+
+#### Scenario: File below threshold is deleted
+- **WHEN** a `.mp3` file in `/home/m/recordings/` is smaller than the configured size threshold and older than 1 minute
+- **THEN** the file is deleted
+
+#### Scenario: File above threshold is preserved
+- **WHEN** a `.mp3` file in `/home/m/recordings/` is equal to or larger than the configured size threshold
+- **THEN** the file is not deleted
+
+#### Scenario: File currently being written is preserved
+- **WHEN** a `.mp3` file in `/home/m/recordings/` was modified less than 1 minute ago
+- **THEN** the file is not deleted, regardless of size
+
+### Requirement: Cleanup runs on a schedule
+The system SHALL execute the cleanup script via a cron job on the Pi host, running every 5 minutes.
+
+#### Scenario: Periodic execution
+- **WHEN** 5 minutes have elapsed since the last run
+- **THEN** the cleanup script executes and removes qualifying files
+
+### Requirement: Size threshold is configurable
+The cleanup script SHALL accept the size threshold as a parameter, allowing adjustment without editing the script.
+
+#### Scenario: Custom threshold
+- **WHEN** the script is invoked with a size argument (e.g., `5k`)
+- **THEN** only files below that size are deleted instead of the default 3 KB
+
+### Requirement: Cleanup script is version-controlled
+The cleanup script SHALL be stored in the project repository so that changes are tracked and deployable.
+
+#### Scenario: Script lives in repo
+- **WHEN** a developer checks the repository
+- **THEN** the cleanup script is present at a well-known path with documentation of its purpose

rtl_airband.conf

@@ -1,5 +1,5 @@
 # RTLSDR-Airband configuration for EU CB radio monitoring
-# Channels: 3 (26.985 MHz), 7 (27.035 MHz), 10 (27.075 MHz)
+# Channels: 3 (26.985 MHz), 7 (27.035 MHz), 10 (27.075 MHz), 16 (27.155 MHz)
 
 localtime = false;
 fft_size = 1024;
@@ -8,7 +8,7 @@ devices:
 ({
   type = "rtlsdr";
   index = 0;
-  gain = 35.0;
+  gain = 25.0;
   centerfreq = 27.035;
   correction = -1;
   mode = "multichannel";
@@ -20,6 +20,7 @@ devices:
       freq = 26.985;
       bandwidth = 8000;
       modulation = "nfm";
+      squelch_snr_threshold = 9.0;
       label = "CB-CH03";
       outputs: (
         {
@@ -35,6 +36,7 @@ devices:
       freq = 27.035;
       bandwidth = 8000;
       modulation = "nfm";
+      squelch_snr_threshold = 9.0;
       label = "CB-CH07";
       outputs: (
         {
@@ -50,6 +52,7 @@ devices:
       freq = 27.075;
       bandwidth = 8000;
       modulation = "nfm";
+      squelch_snr_threshold = 9.0;
       label = "CB-CH10";
       outputs: (
         {
@@ -60,6 +63,22 @@ devices:
           dated_subdirectories = true;
         }
       );
+    },
+    {
+      freq = 27.155;
+      bandwidth = 8000;
+      modulation = "nfm";
+      squelch_snr_threshold = 9.0;
+      label = "CB-CH16";
+      outputs: (
+        {
+          type = "file";
+          directory = "/recordings";
+          filename_template = "CB_CH16_27155";
+          split_on_transmission = true;
+          dated_subdirectories = true;
+        }
+      );
     }
   );
 });