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APRS & Packet Radio

Direwolf, Xastir, APRSdroid, aprx — the modem and map stack for AX.25 / APRS in 2026.

APRS (Automatic Packet Reporting System) is ham radio's GPS / messaging / weather network. Your call goes on the map at aprs.fi; a position beacon every minute, a message-bot reachable by anyone. The underlying packet-radio AX.25 protocol is also still used for BBS / nodes / digipeaters. Cross-link with Ham Rig Control (Hamlib) (CAT integration), LoRa & LoRaWAN (Meshtastic for non-ham mesh comms), Ham Digital Modes, and SDR Direction Finding.

The modem (TNC)

  • ★ Direwolf — software TNC (Terminal Node Controller) by WB2OSZ. The de-facto AX.25 modem in 2026. Decodes 1200-baud AFSK / 9600-baud G3RUH FSK / 300-baud HF / EAS / IL2P / Morse from any sound card; transmits via PTT (CAT or RTS/DTR). Acts as KISS / AGW PE / APRS-IS gateway. Direwolf 1.7+ added IL2P (improved error correction), better DCD, more digipeater modes. GPLv2.
  • soundmodem (DJ7HS) — older Linux software TNC; sunset.
  • TNC-Pi / TNC-X / Mobilinkd / NinoTNC — hardware TNCs; ~$50–150; plug between radio and a computer/phone via Bluetooth/USB.
  • ★ Mobilinkd TNC4 — Bluetooth-LE hardware TNC; pairs with Android (APRSdroid) or iOS (APRS.fi app). The "no PC, just my radio + my phone" rig. ~$120.
  • NinoTNC (N9600A) — kit hardware TNC; G3RUH-capable; for high-speed packet (9600 baud +).

APRS clients / map UIs

  • ★ Xastir — X11 / GTK; the FOSS APRS client. Built-in OSM / Tiger maps, weather alerts, telemetry plotting, station database, message inbox. Linux / Mac. GPLv2. Older UI, deep capabilities.
  • YAAC (Yet Another APRS Client) — Java; cross-platform; modern UI; integrates Direwolf. GPL.
  • ★ APRSdroid — Android; the killer mobile APRS app. Reads GPS, uses internet (APRS-IS) or radio (TNC over Bluetooth) for transport. GPL.
  • APRSpro — macOS; closed; paid.
  • APRSIS32 — Windows; closed; freeware; AC2RJ; long-running; many users.
  • PinPoint APRS — Windows; closed; freeware; modern UI.
  • UI-View32 — Windows; closed; legacy / sunset; the historical default.

APRS-IS gateway / IGate / Digipeater

  • ★ aprx — Linux; Direwolf-companion daemon for running an APRS digipeater + IGate. Lightweight C; the de-facto digipeater software. BSD.
  • APRX-RX-only IGate — popular Pi-based "I just want to feed aprs.fi" setup; aprx in receive-only mode + Direwolf + RTL-SDR.
  • digi_ned / pymultimonaprs — older alternatives.
  • JavaAPRSSrvr — heavy duty APRS-IS server software; runs the major hubs.

Public web map / network

  • ★ aprs.fi — Hessu / OH7LZB's web map; the canonical APRS visualization. Free, closed-source-ish. Your call appears here within seconds of beaconing.
  • aprs2.net — Tier 2 APRS-IS server pool.
  • findu.com — older alternative web map; sunset.

Specialized

  • YAAC's weather / telemetry plotting — for weather-station-on-APRS setups.
  • Ham radio telemetry on APRS — RTL-SDR-fed telemetry; voltage / temperature beacons.
  • RoIP / EchoLink + APRS — APRS messages as gateway commands.
  • Direwolf as KISS modem for Pat (Winlink) — Direwolf can also be the modem for Winlink (worldwide ham email-over-radio); see Pat below.

Winlink / ham radio email

  • ★ Pat (Winlink client) — Go; cross-platform; speaks B2F protocol over Telnet / VHF AX.25 (via Direwolf) / VARA HF / Pactor. The FOSS Winlink client. MIT.
  • Winlink Express (RMS Express) — Windows; closed; freeware; the "official" Winlink client.
  • VARA HF / VARA FM — closed paid (~$70); the modern HF Winlink modem (replaces Pactor for hobbyists). Required for HF Winlink unless you own a Pactor modem.

Mesh / off-grid alternatives

  • Meshtastic — see LoRa & LoRaWAN and MCU Wireless Stacks. Not ham, not APRS — but solves the "off-grid mesh chat / position-share" problem more cheaply.
  • ★ Reticulum / RNS / Nomadnet — newer mesh / cryptographic-overlay network; runs over LoRa, packet radio, TCP, anything. Self-routing, end-to-end encrypted. Growing fast in 2025–26; good ham crossover for licensed packet operators.

Practical guidance

  • APRS frequencies. US: 144.390 MHz; Europe: 144.800 MHz; Australia: 145.175 MHz; Japan: 144.640 MHz. Always 1200-baud AFSK on these frequencies.
  • 9600-baud channels are separate (regional 144 / 432 MHz allocations) and require a 9600-capable radio (with the discriminator audio tap, not just the speaker output).
  • Don't beacon every 30 seconds. Standard beacon rate is 5–10 minutes for fixed stations, faster only for mobile. Spamming the channel makes you the local jerk.
  • Digipeater paths. WIDE1-1,WIDE2-1 is the global standard; older RELAY,WIDE is deprecated. Don't use WIDE3-3 — burns digipeater hops.
  • iGate vs Digipeater. iGate = receive-only, gateways to APRS-IS over the internet. Digipeater = retransmits packets on RF. In a city you don't need another digipeater; you need an iGate. aprx supports both.
  • Direwolf calibration. direwolf -t 5 sends a tone burst — use a service monitor / scope / ear to set transmit deviation correctly (~3 kHz peak). Most setups undermodulate.
  • APRSdroid + Mobilinkd is the most-recommended portable APRS rig in 2026 — phone runs the app, Mobilinkd modems, your HT transmits. GPS from the phone.

License / pricing notes

  • Direwolf / Xastir / YAAC / APRSdroid / aprx / Pat / Reticulum — FOSS (GPL/MIT/BSD).
  • APRSpro / APRSIS32 / PinPoint APRS / UI-View32 / Winlink Express — closed, free.
  • VARA HF / VARA FM — paid (~$70).
  • Pactor modems (SCS PTC / DR-7400) — extremely expensive ($1500+); Winlink HF without VARA used to require these. VARA replaces them for ~$70 + a sound card.
  • aprs.fi — free for personal / non-commercial.

Pick this if…

  • Default Linux APRS / Direwolf modem: Direwolf + Xastir or YAAC.
  • Default Android APRS: APRSdroid + Mobilinkd TNC4 (Bluetooth).
  • Default Windows APRS: PinPoint APRS or APRSIS32.
  • Run an iGate on a Pi: Direwolf + aprx + RTL-SDR or a real radio.
  • Ham email over radio: Pat client + VARA HF + your HF rig.
  • Web map of where my call is: aprs.fi (no install needed).
  • Off-grid mesh, non-ham: Meshtastic or Reticulum.

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