Using the Kenwood TH-D72A with PC APRS Software

Background

The TH-D72A is a very nice handheld Amateur Radio Transceiver. 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.

Capabilities

I intend do demonstrate how to:

  • Use the TH-D72A as the transceiver for a program like Xastir, with full access to the APRS data stream and full simultaneous access to its internal GPS;

  • Use the PC with it without disabling its internal APRS interface

Configuration

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:

  • 1 Set menu 202 to ON (Menu -> GPS -> Int. GPS -> PC Output)

    • This enables GPS sentences in the stream of data sent to your PC. If you run KISS-mode software on the PC, you probably do not want this on, but for more APRS software, it is helpful.

    1 Set menu 350 to ON (Menu -> APRS -> PC Port -> Output -> On)

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.

  • With the TNC completely off, APRS packets will not be decoded and no data will be passed to the APRS network from the PC. The GPS can still be enabled if desired, however, and GPS sentences will be happily delivered to the PC. This can be a nice feature to use with mapping software if you have no need for APRS.

  • In “APRS” mode, the TNC is enabled, and the radio’s built-in APRS user interface is also enabled. This permits the radio to perform APRS tasks without a PC. It can beacon its position, send and receive APRS messages, show nearby stations (LIST button), etc.

    • When a PC is connected to the radio and it is in APRS mode, the PC will receive a full copy of everything the radio receives, but the radio will not transmit anything from the PC.

  • In “PACKET” mode, the TNC is enabled, but the built-in APRS interface is disabled. This mode can be used to give a PC full control over the APRS mode, or to use it for more general packet radio (AX.25) tasks such as connecting to a packet BBS.

    • When a PC is connected to the radio and the radio is in PACKET mode, the PC can indeed transmit APRS packets through the radio. The radio will not generate packets on its own.

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:

tnc-startup.d72

# From https://www.complete.org/amateur-radio
# modified from http://lists.xastir.org/pipermail/xastir/2011-July/020111.html
#Don't send CONTROL-C before this line
##META <no-ctrl-c>
#TC 1
##Pause for one second
##META <delay>
##META <delay>
#Put the TNC in packet mode since this is where we want to end up
# Change the 1 to 0 to go to normal radio mode
##META <no-ctrl-c>
#TN 2,0
# Pause for two seconds
##META <delay>
##META <delay>
##META <delay>
##META <delay>
HID off
AWlen 8
BBSMsgs ON
B E 0
LOC E 0
Echo off
FLow off
AUTOLF off
MCOM off
MON ON
MRPt on
PACLen 128
PASSALL off
HBAUD 1200
TXDELAY 25
HEADERLN off
# Delete following lines if without GPS
#GBAUD 4800
GPSTEXT $GPRMC
#LTMH OFF

tnc-startup.d72-packet

# from https://www.complete.org/amateur-radio
# modified from http://lists.xastir.org/pipermail/xastir/2011-July/020111.html
#Don't send CONTROL-C before this line
##META <no-ctrl-c>
#TC 1
##Pause for one second
##META <delay>
##META <delay>
#Put the TNC in packet mode since this is where we want to end up
# Change the 1 to 0 to go to normal radio mode
##META <no-ctrl-c>
TN 2,0
# Pause for two seconds
##META <delay>
##META <delay>
##META <delay>
##META <delay>
HID off
AWlen 8
BBSMsgs ON
B E 0
LOC E 0
Echo off
FLow off
AUTOLF off
MCOM off
MON ON
MRPt on
PACLen 128
PASSALL off
HBAUD 1200
TXDELAY 25
HEADERLN off
# Delete following lines if without GPS
# GBAUD 4800
GPSTEXT $GPRMC
LTMH
LTM 10
LOC E 0
GPSTEXT $GPRMC

tnc-stop.d72

 STOP FILE
# Undo any settings make in tnc-startup.sys
# Edit this file for your tnc!
UNPROTO CQ
AUTOLF ON
ECHO ON
#Don't send CONTROL-C before this line
##META <no-ctrl-c>
TC 1
##Pause for one second
##META <delay>
##META <delay>
##META <delay>
#Put the TNC in internal mode since this is where we want to end up
# Change the 1 to 0 to go to normal radio mode
##META <no-ctrl-c>
TN 0,0
# Pause for two seconds
##META <delay>
##META <delay>
##META <delay>
##META <delay>
#Turn off Terminal Control
##META <no-ctrl-c>
TC 0
# Pause for two seconds just in case
##META <delay>
##META <delay>
##META <delay>
##META <delay>
#

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:

  • Type: Serial TNC w/GPS on AUX port
  • activate on startup: unchecked
  • allow transmitting: unchecked
  • TNC port: /dev/ttyUSB0 or whatever is appropriate
  • Comment: APRS mode ro
  • 9600 bps
  • 8,N,1
  • Allow RF to Inet traffic ONLY
  • Path 1: WIDE1-1,WIDE2-2
  • Path 2: blank
  • Path 3: blank
  • TNC setup filename: tnc-startup.d72
  • TNC shutdown filename: tnc-stop.d72

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

  • Allow transmitting: checked

  • Comment: PACKET mode rw

  • Igate -> RF path: WIDE2-1

  • TNC setup filename: tnc-startup.d72-packet

Use

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

Amateur radio is a radio service in which people are allowed and encouraged to build their own radios, antennas, and so forth. It can be used to communicate all around the globe without any intervening infrastructure such as satellites or cables.