Summer 2006 Issue

Building an APRS Tracker
Part 1 – The “Nimble” Tracker

APRS and GPS are initials that are enjoying increasing popularity among hams who operate on the VHF-plus bands. Here in part one of a two-part article on building APRS trackers, W2DOE describes how he built a simple APRS tracker using a Garmin eTrex GPS receiver, an ICOM IC-T2H handheld, and a TinyTrac3 TNC.

By Carlton Doe, W3DOE

In an effort to build radio skills as a new ham in 2004, I volunteered for several road races and marathon events. I was told by the communication directors that while they appreciated my efforts, I could be more valuable to them if I had an APRS (Automatic Position Reporting System) tracker. This resulted in my first ham-oriented research and construction project: What was APRS and how would I build what everyone called an “APRS tracker”?

This article will briefly introduce APRS and tell how you can build a simple, low-cost portable tracker. Part 2 will cover construction of a more advanced and powerful tracker. I should explain that as a “bear of very little brain,” I built the harder tracker first before building the one featured in part 1. I did learn a lot in the process, though, resulting in what I think is the simple and elegant “nimble” tracker covered here.

APRS & APRS Trackers

The Automatic Position Reporting System was developed by Bob Bruninga, WB4APR, as an enhancement to regular packet-mode transmission oriented specifically for publishing location-based information via RF. There are two parts to an APRS system: One part transmits where the tracking object is (the job of a tracker); the second part is the display software which receives APRS transmissions and plots the position information on maps. There are a number of software packages, such as UI-View (www.ui-view.org), that can be used to display APRS data. Some of the packages will only work if connected to a radio through either a software or hardware interface. Other packages are internet-aware and can display APRS information gated by digipeaters to APRS internet-based servers. Digipeaters function like the voice repeaters most of you are familiar with, although they handle packet-mode traffic. As a result, you can have a lower power radio yet still achieve broad distribution of your APRS information.1 Many APRS digipeaters are linked to internet-based servers which provide a rolling and filterable archive of position reports the software uses to plot on its maps. APRS software will not be covered in either part of this article.
As I researched APRS trackers on the internet, I didn’t find a lot of useful information other than some pictures. What those pictures showed, though, was that a tracker could be built into almost anything! I saw trackers in which their owners threw the components on the seat of their cars. This violated my sense of aesthetics as well as “professionalism” as an operator. I saw others built in small mint tins, discarded ammo cans, coolers, waterproof cases, and various other containers. Some appeared to have additional “bells and whistles,” while others were very basic.

Photo 1. The Garmin eTrex GPS receiver and its cabling.

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