Secondary Station Identifier (SSID)

In APRS, a callsign can have several SSIDs (suffixes like -7 or -9). Each one is a separate “address” on the network. In classic APRS messaging, you often have to guess which address reaches the person you want. Radio Messenger treats that the way modern messaging apps treat phone numbers: you talk to a person by callsign, and the app figures out the right SSID when it can.

One thread per callsign

Conversations are grouped under the base callsign, not split into a separate thread for every SSID. That matches how most people think about messaging: one ongoing chat with WH6AZ, not three parallel chats with WH6AZ-7, WH6AZ-9, and WH6AZ-15.

Each message still keeps its full callsign + SSID attribution. Long-press a message and tap Details to see the complete source, destination, and path.

Messages you receive

The app shows any message addressed to your callsign, on any of your SSIDs. You do not need to pick which identity is “active” to see incoming traffic.

When the network expects an acknowledgement, the app sends an ACK only for messages addressed to the exact SSID that actually received the packet. That keeps you compatible with traditional APRS stations and gateways that expect a precise reply.

Messages you send

When you reply, the app sends from the SSID you are using now (the one tied to your settings).

When you start or continue a conversation, outgoing messages are addressed to the SSID that looks most reachable for that station. By default that is the most recently active messaging-capable SSID (the one that last sent you a message you could reply to).

Likely reachable at

When you open a station profile, you see a hint such as Likely Reachable At: WH6AZ-7. That is the app’s best guess for where to deliver your next message, not a guarantee.

The guess combines:

• Recent messages from that station (which SSIDs have been used for messaging lately).
• Position and status traffic (which SSIDs look like a live operator rather than infrastructure, such as a weather station).

The hint updates as new traffic arrives. If you know a station only checks one radio, you can still rely on the automatic choice in most cases.

Why this approach

For human-to-human messaging, the usual goals are:

1. Show you everything sent to any of your SSIDs.
2. Acknowledge only what arrived on the SSID that actually heard it.
3. Reply from the SSID you are using now.
4. Keep one conversation per callsign.
5. Pick a reachable SSID for the other station when you do not want to choose yourself.

Radio Messenger follows that model so APRS messaging feels closer to a familiar chat app, while still working with operators and services that use classic APRS addressing.

When you might change your SSID

Leave the default SSID in Settings unless you run another app or radio that needs a separate identity. See Getting started for setup. If automatic addressing ever feels wrong for a station, check Details on recent messages to see which SSIDs have been active.