APRS Connect

Bluetooth KISS TNCs

A radio or TNC with built-in Bluetooth Classic KISS — a Kenwood TH-D74 or TH-D75, or a Mobilinkd TNC3 — connects to APRS Connect with no cable at all. This guide covers pairing, adding the channel, and the settings that matter.

If your TNC is a Bluetooth Low Energy device — a Mobilinkd TNC4 in LE mode, or a B.B. Link — it works differently and has its own guide. Not sure which you have? A Classic TNC appears in Android's Bluetooth settings and can be paired there; a BLE TNC never does.

Pair in Android first

Pairing is handled by the system, not the app. Before anything else:

  1. Put the radio or TNC in its Bluetooth pairing mode (see its manual).
  2. Open Android's Settings → Bluetooth and pair it like any other device.

If you skip this, the app's device list will tell you exactly that: "No paired devices. Pair your radio in Android Bluetooth settings first, then come back — pairing is handled by the system."

Add the channel

  1. Open the Radio screen (under More on the tab bar) and tap Add channel.
  2. Pick Bluetooth TNC — "A paired KISS TNC — Mobilinkd, TH-D75, and friends".
  3. The Paired devices list appears, holding every Bluetooth device paired with the phone. Anything that looks like a TNC — a Kenwood TH-D, a Mobilinkd, anything with TNC, KISS, or APRS in its name — is sorted to the top and tagged LIKELY TNC.
  4. Tap your radio. The channel connects, and if you haven't named the channel yet it adopts the device's name — "TH-D75" says more than "Bluetooth TNC".

The first time through, Android asks for the nearby-devices (Bluetooth) permission; the list can't load without it.

One radio holds the link at a time: the phone has a single Bluetooth Classic connection, so choosing a device here switches off whichever other Bluetooth channel was using it — and the switch says so before you tap.

Put the radio in KISS mode

The Bluetooth link only carries bytes; the radio end has to speak KISS. On radios with a built-in TNC — the Kenwood TH-D74 and TH-D75 — that means switching the TNC into KISS mode (not APRS mode, where the radio runs its own APRS client) on the band you want to use for packet. A Mobilinkd TNC3 speaks KISS natively and needs no mode change.

This is the single most common setup problem, and the app watches for it: a channel that connects but never hears anything shows "Connected but nothing received yet. If this persists, check the radio is in KISS mode." A connected link with a rising received counter means you're done.

Settings on the channel

  • Transmit delay — the tone sent before the data, so the far radio's receiver has settled before your packet starts. It's sent to the TNC each time the link comes up; a TNC with its own transmit-delay setting may use that one instead.

Troubleshooting

  • "Bluetooth is switched off" — turn Bluetooth on; the channel reconnects on its own.
  • "Bluetooth permission denied" — grant the nearby-devices permission in system settings; the error message has a button straight to them.
  • Connected, nothing received — check KISS mode (above), the radio's volume, and that you're on an APRS frequency with traffic. The channel row shows CONNECTED · QUIET with an explanation when the link is fine but the frequency has no traffic — that state is not a fault.
  • The radio pairs but the app can't connect — make sure no other app (or another phone) holds the radio's Bluetooth link. Each channel row has its own RECONNECT button.

Next steps

Last updated 31 August 2026

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