APRS Connect

Bluetooth KISS TNCs

A radio or TNC with built-in Bluetooth Classic KISS, such as 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, such as 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 on the tab bar and tap Add channel.
  2. Pick Bluetooth TNC, described as "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 is sorted to the top and tagged LIKELY TNC. That covers a Kenwood TH-D, a Mobilinkd, or anything with TNC, KISS, or APRS in its name.
  4. Tap your radio. The channel connects, and if you haven't named the channel yet it adopts the device's name, because "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 the Kenwood TH-D74 and TH-D75, which have a built-in TNC, 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 is 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.
  • KISS port says which radio on the TNC this channel is. Leave it at 0 unless the TNC has more than one radio behind one link; see Two radios on one TNC.

TNC battery

A Mobilinkd TNC3 reports its own battery level over the Bluetooth link, and the channel row on the Radio screen shows it, with a notification when the pack gets low. Only Mobilinkd hardware is asked for it; a TH-D74 or TH-D75 is never sent the query. The BLE TNC guide has the details.

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, which 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.

In the Windows app

Bluetooth Classic TNCs also work in the Windows app. Pair the radio or TNC in Windows Bluetooth settings first. Windows gives a paired device a serial port, and the app lists the paired devices that have one. Add a Bluetooth TNC channel on the Radio screen and choose the radio. The first connection can take several seconds while Windows opens the link.

Next steps

Last updated 23 September 2026

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