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Using the Kenwood TH-D72A with PC APRS Software


The TH-D72A is a very nice handheld radio. Among other things, it has an integrated GPS, built-in APRS functionality, full AX.25 packet radio TNC, and a USB port (which shows up as a serial device) to a computer -- all built in.

While it is perfectly useful in a standalone configuration, sometimes the larger screen and full keyboard of a real computer are beneficial. Software such as Xastir can present APRS information on a map.

I am writing this page because there is a lot of misinformation about the TH-D72A out there -- and also a lot about it that is under-documented.

While I personally use Xastir, this information should also be relevant to users of UI-View and other APRS software as well. Also, the TH-D72 is very similar to the TM-D710/TM-D710A, so much of what is said here may also apply to that mobile rig.


I intend do demonstrate how to:


Before beginning, you need to make sure the TH-D72A has at least firmware version 1.03. You can find the firmware version by holding the ENT/# key while you turn the unit on. You should see "Main Firmware 1.03" (or above). If you need an upgrade, find it from Kenwood's website.

Next, configure the TH-D72A to send relevant information to the PC or laptop. The appropriate places are:

Two modes

Pressing the TNC button on the radio switches between three modes: TNC off, APRS mode, and PACKET mode. Let me describe them, and how they interact with the PC.

Crucially, so long as menu 202 is set to on and the GPS is enabled, GPS sentences are sent to the PC via the USB cable in all three modes. This is exactly what we want for PC APRS software, though it might not be for some other things.

Configuration of Xastir

I have configured two Xastir interfaces for use with the TH-D72A: one for the unit's APRS mode, which is a read-only interface; and the other for its PACKET mode, which is a read-write interface. Why two? Well, sometimes it might be nice to have the laptop as a passive receiver of APRS data; for instance, feeding it onto APRS-IS via a tethered cell phone, or simply available in case I want to look at it, but not required all the time.

TNC initialization scripts

You'll need these initialization scripts. They are lightly modified from the D710 scripts I found on the web.

Copy and paste them into files in your Xastir configuration area. On my system, it's /usr/share/xastir/config. You're found the right spot if you see files with names like tnc-startup.sys in there.

Here are the files:

Add the Interfaces

Now, open Xastir. Go to the Interfaces menu and select Interface Control. You're going to click Add to add an interface, and do it twice.

Configure the first one like this:

Configure the second one the same, except with these differences:


Now it's ready to use. Before beginning, you'll of course plug in your USB cable. You'll also want to make sure the menu options 202 and 350 are configured as listed above. Now, press TNC until APRS shows up on the radio's display.

Next, in Xastir, go to Interface -> Interface Control. Select the mode you want ("APRS mode ro" for Xastir to have a read-only interface and leave the APRS interface active on the radio, or "PACKET mode rw" for Xastir to be able to transmit but disable the radio's packet interface). Click Start, wait a few seconds, and you're set. If you selected Xastir's PACKET mode, you should see the display on the radio change from APRS to PACKET12. If you selected Xastir's APRS mode, the radio display should continue showing APRS.

All done!

Notes on Firmware Versions

After some discussion on the Xastir list, the above steps didn't work out for everyone. Tom Hayward KD7LXL reported this:

I was able to test with a dumb terminal. I sent each of the TNC mode
commands and watched the output for NMEA strings.

TH-D72 v1.02:
TNC off: GPS output works
TNC APRS12: GPS output works
TNC PACKET12: no GPS output

TH-D72 v1.03:
TNC off: GPS output works
TNC APRS12: GPS output works
TNC PACKET12: no GPS output

This seems to confirm the bug we've been seeing all along is also
present in 1.03.

It seems that as of 1.05, there is no firmware version with GPS output works in PACKET12 mode.

See Also

WikiCompleteOrg: THD72PCAPRS (last edited March 22, 2012 by JohnGoerzen)