APRS safety and the kill switch

Signing out, losing your callsign verification, or HAMORA Bridge’s SWR/ALC lockout also stop sending. Phones and HAMORA Bridge’s setup page can only add stops. Switching the TX master back on, clearing an E-STOP and approving a phone happen only at the HAMORA Bridge computer. Only HAMORA can lift its kill.

• On the phone: Stop transmitting (E-STOP), in the APRS station settings under RF through HAMORA Bridge (in the builds being tested; the wording isn’t final). HAMORA asks you to confirm, then tells HAMORA Bridge to stop.
• Also from HAMORA Bridge’s setup page, or on the HAMORA Bridge computer.
• What it does: HAMORA Bridge stops handing packets to the radio and refuses all transmitting, for every phone. Its queue is emptied in under 250 milliseconds.
• Clearing it: only on the HAMORA Bridge computer. No phone, setup page or message from HAMORA Cloud can clear it.
• If the phone can’t reach HAMORA Bridge, the E-STOP isn’t engaged, and the app says so. Then stop it on the HAMORA Bridge computer, or switch the radio off.

A packet already handed to the TNC can’t be recalled, so one packet, about 2 seconds of airtime at most, may still go out.

• HAMORA can stop all APRS sending remotely. Any kill, for everything or for APRS only, stops sending in the app and on HAMORA Bridge, on APRS-IS and by radio.
• Kills are signed by HAMORA and checked on the phone and on HAMORA Bridge. A kill stays in force across restarts until HAMORA sends a newer signed clear.
• Nobody can lift a kill locally: not the HAMORA Bridge computer, its setup page or a phone.
• On HAMORA Bridge, a kill empties the queue in under 250 milliseconds.
• HAMORA’s kill only ever stops sending. It can never start it.

If HAMORA can’t confirm it’s safe to send, nothing is sent.

• If the phone or HAMORA Bridge can’t confirm the kill status, because it’s missing, too old or can’t be verified, sending is refused until a fresh, signed status arrives.
• On HAMORA Bridge, a kill status that goes stale empties the queue, like a kill.
• If HAMORA Bridge can’t read its own switch settings, it acts as if transmit is off and the E-STOP is engaged, until that’s fixed at its computer.
• Anything else that can’t be checked, such as the radio’s frequency, the clock or the audit log, also means no.

• While a packet goes out, HAMORA Bridge reads the radio’s SWR and ALC through the CAT connection, about ten times a second, read-only.
• A high reading locks that radio out: its queue is emptied at once, and every new request for it is refused.
• The lockout is cleared only at the HAMORA Bridge computer, after you check the antenna and feed line. It survives a restart. No phone or setup page can clear it.
• It applies to APRS only.
• A radio that can’t report SWR and ALC is refused, unless you choose otherwise, explicitly, in HAMORA Bridge’s settings on its computer.
• The thresholds are proposed, not final.

• For each radio, at most 5 packets wait at HAMORA Bridge, and 1 is at the TNC.
• The queue is in memory only. A restart empties it, and nothing waiting goes out afterwards.
• If the TNC goes away, its queue is emptied: nothing goes out in a burst when it’s back.
• Sending by radio happens only while HAMORA is open on screen.
• Automatic beacons by radio are off, behind a setting that stays off.
• HAMORA Bridge also limits how often and how long each radio sends. The values are proposed, not final.

More on how the queue works: APRS over radio.

• Operate within your licence privileges and your local band plan.
• Verify your local APRS frequency yourself, against your local band plan. HAMORA keeps no licence or frequency tables.
• Never leave a station transmitting unattended.
• If anything looks wrong, use E-STOP at once, or switch the radio off. Then find out why before you clear it.
• Check your antenna’s SWR before you go on air, and use the lowest power that works.
• Your callsign is in every packet. Whether that alone meets your country’s station identification rules is being confirmed by HAMORA’s legal review; follow your own rules in the meantime.