Nick Taylors blog

I’ve finally installed Mobile APRS in the Green D90. I’ve had static APRS working, but it was time to integrate GPS into the system; particularly useful when we head out to remote locations as we do most weekends.

The original plan was to simply send the trucks current coordinates as acquired by the GPS via a TNC to the radio and out, to be picked up by other stations and relayed to an igate and from there onto the internet where many various sites show your position in near real-time.

This would have been a very simple setup consisting of a Garmin GPS16HVS, an OEM unit that basically integrates the GPS and antenna into a single unit without a display, a Kantronics MT-1200 TNC and an Icom IC-2200 single band radio.

However, I ran out of time (I wanted it working for our Utah “Hole in the Rock” trip), and didn’t want to go back to Radio Shack for another 2.5mm 3 way jack so I dug out my “spare” Kenwood TM-D700A, which has a built it TNC and would save some time during the configuration.

With the Kenwood radio, the system simply consisted of the GPS16 connected to the D700A radio.

Installing the GPS16 was a small problem. It comes with a magnetic mount, which, of course, is no use in an aluminum-bodied Land Rover Defender (actually, it’s Birmabright). The green D90 is a bit old and beat up anyway, so I wasn’t too bothered about drilling the roof. I drilled 4 holes for the GPS16 and another 4 for the cable passthrough (a waterproof marine-grade “Cable Clam“, made by Blue Sea Systems and available from from West Marine), and simply fed the cable through.

The GPS16 ships with an RJ45 connector, and I can’t imagine what use it has except for factory testing. After cutting it off, there are basically 2 sets of data wiring and also power wires in a very compact space (as described in the manual – PDF link). It’s a simple job, but fiddly connecting the power to my usual 45A Anderson Powerpole connectors and a 3-way 2.5mm jack. Initially I forgot that the data ground has to be cross connected to the ground, so the GPS did not switch on.

I removed the 2.5mm jack and connected an DB9 socket so I could connect a terminal to the GPS16. It was about now I realized that it wasn’t powered on (there is no indicator light to show this), but I was amising myself watching the NMEA sentences appear on my terminal. I also downloaded the Garmin SNSRCFG software, which enabled me to play with a ton of settings in the GPS16. I just made sure the data it was acquiring was correct before disconnecting it and putting the 2.5mm jack back on.

Then, I connected the jack to the radio and to my delight I saw the GPS indicator flashing, meaning that the radio was receiving telemetry from the GPS. Fiddling with a few settings on the radio, to configure it to take position data from the GPS and override the manual co-ordinates I’d entered earlier, I saw the “MY POS” indicator flash up, showing that APRS data was being transmitted. A drive around the block and a quick visit to db0anf, and I could see my position being updated in near real time. Success!

You can see my position updates here.

Overall, the Garmin GPS16 and Kenwood TM-D700A radio is a great combination for hands off APRS work.

I do have a few more steps to finish this little project, including making a small breakout box for the GPS16, which will have switched power and a connection for both the radio (via a jack) and terminal (via a DB9). And then I’ll have to do it all again for the black D90!