First install Xastir on your Raspberry Pi. Have a look here:
Connect your Kennwood TH-D74 with the original USB cable to the USB port of the Raspberry Pi. I have noticed that not all USB cables are suitable. Probably some can only be used for charging and do not transfer data.
If you like to use a bluetooth connection have a lock here:
Set the desired APRS frequency on the TH-D74 and activate the KISS mode
In the TH-D74 settings, set the USB function to COM+AF/IF Output
Set PC Output (APRS) and KISS to USB
I don’t use the internal GPS of the TH-D74 because I already use a USB GPS dongle (for the time synchronization of the Raspberry Pi) . I haven’t tried it but it should be possible to use Xastir and the TH-D74 with the internal GPS. See available Xastir interface types
Now it is necessary to find out at which USB port the Raspberry Pi recognized the TH-D74. The easiest way to do this is with the terminal and the command
ls -l /dev/serial/by-id
ttyUSB0 is my CAT cable from the Elecraft KX2
ttyACM0 is my Kenwood TH-D74
ttyACM1 ist my USB GPS dongle
Important: Check that the USB port settings for USB GPS (sudo nano /etc/default/gpsd) and Xastir (interface) are correct and not the same. If the same USB port is specified twice, it will not work correctly.
Have a look to my Xastir Interface setting, it works great.
It is possible to create several interfaces of the same type. So I use one interface for my TH-D74 for APRS on a “normal” frequency (Path WIDE-2-2) and another interface of the same type (Path ARISS or RS0ISS – check what will work) for APRS over ISS. The desired interface is then activated. Multiple interfaces of the same type, on the same port, at the same time are not possible.
A sound modem (such as direwolf) is not required for this setup, since the KISS TNC is already present in the TH-D74. I use direwolf for Packet Radio on KW with my Elecraft KX2 or for VHF/UHF devices that do not have a built-in TNC.
APRS with Raspberry Pi, Xastir and TH-D74, is that easy 😉
Have fun… VY 73, Karl-Heinz, DL1GKK