APRStac is an APRS web client, digipeater, I-Gate, BBS, fileshare host, email gateway, and multi-protocol bridge developed by KN4MKB under the ModernHam project. The software is distributed as a single binary with no external dependencies and runs on Windows, Linux, Android, and Raspberry Pi. The interface is delivered through a local web server that can be accessed from any browser on the local network.

Core Architecture

APRStac operates as one process that handles multiple APRS roles traditionally covered by separate applications. On first launch, the program creates a default configuration file aprstac.toml and a SQLite database aprstac.db in the working directory. The web interface opens automatically at http://localhost:14501. Network access from other devices is disabled by default and can be enabled in Settings → General. Once enabled, the server binds to 0.0.0.0 and becomes available to other devices on the LAN.

Station parameters including callsign, SSID, symbol, and position are configured in Settings → Station. Transmission is blocked until a callsign is set. The default tocall is APRTAC. GPS modules are supported for automatic position updates.

Port System and Protocol Support

All input and output data flows through configurable ports. Supported port types are listed in Settings → Ports:

KISS Serial: Connects to hardware TNCs over serial ports such as /dev/ttyUSB0 or COM3. Standard baud rates like 1200 or 9600 are selectable.

KISS TCP: Connects to software TNCs such as Direwolf, SoundModem, or VARA in KISS mode using host and port settings.

APRS-IS: Connects to the APRS Internet System on port 14580 with callsign and passcode authentication. Bidirectional IGate functionality is optional.

UDP Broadcast: Shares packets on the local network via UDP port 14581. Multiple APRStac instances on the same LAN can exchange packets without manual IP configuration.

Meshtastic TCP and Serial: Bridges Meshtastic LoRa devices over network or USB. Two traffic types are handled. Native Meshtastic node positions can be imported to the map with a badge and remain local only. Real APRS frames sent by other APRStac stations over Meshtastic use a private portnum and retain full packet integrity. These frames are treated as RF traffic and are eligible for digipeating and IGating.

VARA FM: Connects to a VARA FM modem for connected-mode sessions. Current usage is limited to BBS and Fileshare operations.

Reflector Server: Hosts a private encrypted APRS reflector. The server listens for TCP connections and redistributes all received packets to connected clients. Traffic is AES-256 encrypted using a shared password.

Reflector Client: Connects to a remote Reflector Server using hostname, port, and password. Packets received from the reflector are parsed and displayed as standard APRS traffic. Local packets are forwarded to the server for distribution.

APRStac Public Reflector: A pre-configured client that joins the public encrypted reflector at aprstac.com. No setup is required. Connected stations are visible at aprstac.com/map.html.

TAK: Bridges to Team Awareness Kit servers using mTLS authentication. Cursor on Target events are translated to and from APRS for position and message exchange.

Digipeater and IGate Functions

The digipeater repeats packets across enabled ports. Cross-medium repeating is supported. A packet heard on Meshtastic can be repeated out a KISS port, to a Reflector, and over UDP simultaneously. Repeating requires several conditions: global digipeater mode must be enabled, the source cannot be an operated callsign, the path must not contain TCPIP or TCPXX, the packet must contain WIDEn-N, TRACEn-N, or RELAY with remaining hops, the packet must not be a duplicate within 30 seconds, and the destination port must have digipeating enabled.

The IGate provides RF to APRS-IS and APRS-IS to RF forwarding. Messages from APRS-IS are gated to RF for stations recently heard on local ports.

Mapping and Station Data

The web interface uses a Leaflet map. Features include live station tracking with heading arrows, Maidenhead grid overlay, MGRS coordinates, and configurable station ghosting for stations that have stopped beaconing.

Status Reporting: Stations can broadcast readiness levels for eight categories: Food, Water, Shelter, Power, Medical, Comms, Fuel, and Personnel. Each category is set to Green, Yellow, Red, or Unknown. Reports are sent as standard APRS status packets. Received reports appear as colored chips in the station info box and in a dedicated Status Report table that auto refreshes every 30 seconds.

Sensor Tracking: Weather telemetry for temperature, humidity, pressure, wind, and rainfall is logged per station. Interactive charts display historical data with selectable time ranges.

Offline Maps

Two offline options are provided. The tile cache stores OpenStreetMap tiles in tiles.db with LRU eviction and a configurable size limit, default 10 GB. Supported layers include street, topo, satellite, and dark. MBTiles support allows fully offline operation. Raster .mbtiles files placed in the mbtiles/ directory can be selected in Settings → Map. Three modes are available: OSM Only, MBTiles Only, and OSM + MBTiles Fallback. Vector PBF tiles are not supported and are flagged by the UI.

BBS

APRStac includes an AX.25 connected-mode BBS accessible over RF, Meshtastic, VARA FM, and TCP links. Hosting requires a unique BBS callsign separate from other station callsigns. Optional features include a custom welcome message, periodic beacons that can append unread message callsigns, and storage limits with automatic pruning.

Standard BBS commands are supported. Public posting commands include L for list, R for read, and P for post. Private message commands include S for send, M for messages, O for open, U for unread, D for delete, and E for exit. Commands are case-insensitive and prompts are provided for missing arguments. Posting and messaging can also be managed through the web interface without an RF connection.

When connecting to another APRStac BBS, the client detects the remote system and presents a modern web interface with action buttons. Connections to non-APRStac systems use a traditional terminal view. A toggle allows switching between modes.

Fileshare

The fileshare system transfers files over AX.25 connected mode. Hosting requires a unique fileshare callsign. Files up to 10 MB are uploaded through the web interface. On upload, APRStac compresses files using zstd, gzip, and brotli, then stores the smallest result. If compression does not reduce size, the original is stored.

To download, a connection is made to the remote fileshare callsign and the file list is retrieved. Files transfer as base64-encoded chunks in I-frames with MD5 checksum verification. Compressed files are decompressed automatically on arrival. Transfers operate over RF, Meshtastic, VARA FM, and TCP links.

Email Gateway

The email gateway forwards APRS messages to email and allows email replies to be sent as APRS messages. Configuration requires SMTP and IMAP server details, credentials, a listen callsign, and a recipient address. Gmail, Hotmail, and Yahoo are not supported due to IMAP and SMTP restrictions. Patreon supporters receive an aprstac email account.

Sending from APRS requires addressing a message to the listen callsign with the format recipient@example.com Message text. The first word is parsed as the destination address and the remainder becomes the email body. Replying from email requires setting the destination callsign in the subject line and writing the message in the body. APRStac polls IMAP and transmits the body as an APRS message. The APRS message limit of 67 characters applies.

Meshtastic Integration Details

Meshtastic ports support both native node positions and tunneled APRS frames. Import Nodes pulls positions from mesh handshakes and ongoing broadcasts. Tunneled APRS frames preserve source callsign, digipeater path, and info field. These frames participate in the APRS network and can be IGated and digipeated. Connected-mode BBS and Fileshare sessions over Meshtastic use relaxed AX.25 timers to accommodate mesh latency.

Notifications and Discord Webhook

Discord webhooks post APRS packets to a channel as formatted embeds. Setup requires creating a webhook in Discord and pasting the URL in Settings → Notifications. Packet types for forwarding are selectable and include Position, Messages, Weather, Objects, Telemetry, and Mic-E. A per-station rate limit controls posting frequency. Each embed includes callsign, decoded data, raw packet, and a link to aprs.fi for packets with position data.

Mobile Access

The web interface is responsive and functions on mobile browsers. This allows remote access to a desktop or Raspberry Pi instance from phones or tablets on the same network. A dedicated Android app includes a built-in AFSK modem for standalone operation or for remote access to a base instance.

TLS and Reflector Mode

HTTPS is supported with TLS certificates. Paths to fullchain.pem and privkey.pem are set in aprstac.toml. When configured, the server uses HTTPS instead of HTTP. The --reflector command line flag starts APRStac in reflector-only mode. This launches a Reflector Server on 0.0.0.0:14502 and a view-only map on 0.0.0.0:14501. The encryption password is hardcoded to aprstac.com. This configuration is used for the public reflector map.

Technical Notes

APRStac stores configuration in TOML and operational data in SQLite. The application identifies on the APRS network with the tocall APRTAC. VARA FM ports are currently restricted to BBS and Fileshare use. MBTiles support is limited to raster formats. The email gateway requires a mail server that permits third-party IMAP and SMTP access. All Reflector traffic is AES-256 encrypted end-to-end.

Bugs and issues are reported to report@aprstac.com. The project is maintained by KN4MKB under the ModernHam banner.

https://aprstac.com/index.html

The post APRStac: A Modern APRS Suite in a Single Binary appeared on Hamradio.my - Amateur Radio, Tech Insights and Product Reviews by 9M2PJU.