RadioMail can pair with KISS TNC modems to connect to stations via the Robust Packet packet protocol.

Robust-Packet (RPR, Robust Packet Radio) is a data transmission mode devised from Special Communications Systems GmbH & Co. KG. It is optimized for the deployment in the short wave band. To accommodate the characteristics of this frequency range, for example fading and multipath propagation, a eight carrier OFDM is used.

RadioMail supports zero configuration TNC device discovery as described in those specifications:

• Specification for KISS over BLE (Bluetooth Low Energy)

LiNK500 is a portable, Robust Packet TNC with built-in Bluetooth LE support. To setup a LiNK500 device, follow these steps:

1. Turn on LiNK500. Make sure no other application is paired with the device.
2. In RadioMail, tap Settings -> Robust Packet KISS TNC Modem
3. Tap Default TNC
4. RadioMail will search for nearby devices. When your device appear, tap on its name, for example "LiNK500"
5. Tap Done

When connecting to robust packet stations, the default TNC device will be used.

If the device does not appear, ensure that Bluetooth is enabled and that RadioMail has permission to access Bluetooth. Go to iPhone Settings -> RadioMail and verify that Bluetooth access is enabled.

For the LiNK500 to function as a BLE TNC, it must be in KISS mode. Connect the device to a serial terminal and issue the following command:

ESC@KP1
ESC%ZS

This will ensure that the device will always restart in KISS TNC mode.