APRS over radio

As designed:

1. You write a message, or ask for a beacon, in HAMORA on your phone, and choose radio for it.
2. HAMORA sends the packet’s fields, never ready-made bytes, to HAMORA Bridge on your own network.
3. HAMORA Bridge checks everything again, builds the packet itself and queues it.
4. When the TNC is free, HAMORA Bridge hands it the packet: Dire Wolf over KISS on the network, or a hardware KISS TNC on a serial port.
5. The TNC turns it into tones, and your radio sends it.

The app never says a packet was “sent on air” or “delivered”. The furthest it can say is Handed to the TNC: KISS can’t confirm the radio sent it, and only an acknowledgement shows another station heard it.

• Sending through HAMORA Bridge works only on your own local network, between your phone and the HAMORA Bridge computer.
• It never goes through HAMORA Cloud Relay. HAMORA Bridge accepts a transmit request only from a local address, with no forwarding, so HAMORA Cloud Relay can never reach it, whatever it carries.
• Never forward HAMORA Bridge’s port or your TNC’s port from your router to the internet.

• HAMORA Bridge builds every frame itself, AX.25 inside KISS, from checked fields. It never passes on raw bytes from a phone.
• Only messages, acknowledgements and position reports, in the exact form HAMORA sends them. Anything else is refused.
• It sends the TNC data frames only, never settings. Your TNC’s own timing and channel checks stay in charge.
• Two kinds of TNC: Dire Wolf over KISS on the network (kept on the HAMORA Bridge computer), or a hardware KISS TNC on a USB serial port.
• Your callsign must be 6 characters or fewer for AX.25. HAMORA never shortens it: a longer callsign can’t send by radio.

The set-up is in APRS hardware set-up. Which TNC set-ups the controlled beta proposes, and how far each has been checked, is in the beta’s set-ups.

• For each radio, at most 5 packets wait at HAMORA Bridge, and 1 is at the TNC. The next one is handed over only after the last one has had time to go out.
• The queue is in memory only. A restart empties it: nothing waiting goes out afterwards.
• E-STOP, switching transmit off, revoking a phone, a kill, or a kill status that’s too old empties the queue in under 250 milliseconds, and new requests are refused.
• If the TNC goes away, its queue is emptied. Nothing is saved up to go out in a burst when it comes back.

• Frequency and mode read back. Before each packet, HAMORA Bridge reads the radio’s frequency and mode over a CAT cable, and refuses if they aren’t the APRS channel set up for it. HAMORA Bridge never changes the frequency itself.
• Or a dedicated radio. A radio with no CAT link can be marked as a dedicated APRS radio, only in HAMORA Bridge’s settings on its computer. Nothing can then watch its SWR or ALC, so that needs a second, explicit local acknowledgement.
• SWR/ALC lockout, for APRS only. While a packet goes out, HAMORA Bridge reads the radio’s SWR and ALC. A high reading locks that radio out at once and empties its queue. The lockout stays until it’s cleared at the HAMORA Bridge computer, after you check the antenna and feed line. The limits are proposed, not final.
• Rate and airtime limits per radio. HAMORA Bridge spaces positions and messages and caps how much of the channel you use. The values are proposed, not final.

More in APRS safety and the kill switch.

HAMORA Bridge sends for a phone only when all of these are in place:

1. the phone asked for radio access, and you approved it at the HAMORA Bridge computer, with the code the phone shows;
2. each request is signed with that phone’s own device key;
3. the phone holds a current operator credential for your verified callsign;
4. the TX master switch on HAMORA Bridge is on. It’s off to start with, and only the HAMORA Bridge computer can switch it on;
5. the callsign in the packet is HAMORA Bridge’s station callsign, and yours;
6. no E-STOP, no kill, and a recent, confirmed kill status from HAMORA.

Radio access is separate from any other HAMORA Bridge permission: it grants nothing else, and nothing else grants it.

In the builds being tested, the APRS station settings have a section called RF through HAMORA Bridge. The wording isn’t final.

• Send on RF is off until you switch it on, and HAMORA asks you to confirm each time: radio is public and not encrypted, it goes out from your own radio as your callsign, and you’re responsible for operating within your licence.
• Ask for access shows an approval code to enter at the HAMORA Bridge computer.
• What still stops RF lists every reason HAMORA Bridge won’t send yet, in words.
• Stop transmitting (E-STOP) stops HAMORA Bridge sending for every phone.
• Sending by radio happens only while HAMORA is open on screen. Leaving the app drops what’s in flight.
• Each conversation and each beacon uses one link, radio or APRS-IS, never both and with no fallback.
• HAMORA never adds its “via HAMORA” text to anything sent by radio.

• Digipeat, or act as an IGate in either direction.
• Pass APRS-IS traffic to radio.
• Send objects, items, telemetry or bulletins.
• Send automatic beacons by radio: a setting keeps them off.
• Accept a request from outside your local network, or send while HAMORA is in the background.