APRS Trackers For All!
In the Spring 2013, HOTARC Directors and Members agreed to apply a generous donation from the Waco Bicycle Club to finance a project to provide affordable APRS Trackers to Club Members. The project subsidized about half of the ~$220 cost of assembling a 5W APRS tracker based on a design by W5NCD that incorporates the Byonics TinyTrak into the battery case of an HT, as pictured here. While the trackers could be used by members for their own personal benefit, the Club reserved the right to "borrow" the subsidized trackers for Club functions and special events, such as the annual WWW100 event.
Tips for new APRS trackers
Here are a few tips for those new to APRS tracking.
1. GPS Signals. After starting up your tracker, allow a few minutes for the GPS unit to lock onto and gather enough data from the overhead cloud of GPS satellites to begin sending out your position reports. Some GPS receivers include a little LED indicator (blinking or not). Of course, the GPS receiver needs a clear view of the sky—not blocked by roof, garage, carport, etc. So, using the acquired satellite data, every tracker knows its exact location and the exact time of day (important for "time slotting" described below...).
2. General Radio Setup. The handheld transceiver should be set to transmit full power (~5W) on 144.39 MHz simplex for everyday APRS operation. Of course, you can also use the radio on other amateur frequencies (whether for APRS or otherwise), but to get into the APRS network, you must use 144.39 MHz. The TinyTrak chip needs a moderate volume level. Adjust the squelch to open when other nearby APRS signals are heard, but NOT remain open continuously. After adjusting, we recommended "locking" the keypad to avoid inadvertent changes.
3. Switch on the back. The W5NCD tracker design includes a switch on the battery case for TinyTrak configuration. The Left (normal) position is good for everyday driving. "SmartBeaconing" sends out position reports when you turn corners, otherwise every 5 minutes or so. You can see the results on aprs.fi or openaprs.net, but don't expect every single packet to make it into the system and show up on the map: some of your packets inevitably are not heard for various reasons (out of your control). The Right (special event) setting sends out a position report every 2 minutes, at a specific "slot" of time (seconds) past the top of the minute (part of YOUR tracker's configuration). This "time slotting" helps prevent multiple trackers in a special event from sending packets at the same time.
4. Is it working? As noted above, if you're within range of an APRS receiving station, you should see your position reports on aprs.fi or openaprs.net in your web browser. If you have another mobile rig in your vehicle, you can listen for your 144.39 MHz tracker transmissions, but expect to also hear other local packet activity on that frequency. Clever hint: To monitor only your tracker, tune your mobile rig (NOT THE TRACKER) to the first harmonic frequency: 2 x 144.39 = 288.78 MHz, and only strong signals will get through your filters. When you hear a packet transmission on this harmonic frequency, you'll know your tracker just sent out a position update. (Is there also a second harmonic: 3 x 144.39? Try it!)
5. Power considerations. The 5-watt tracker radios and other electronics are powered by the 12V cigarette lighter plug, and the radios we've selected for our trackers are generally configured to come ON as soon as power is supplied. Bear this in mind, if you leave the tracker plugged in continuously. Depending on your brand of auto, you may want to connect to power through a switched accessory source rather than the cigarette lighter. Also, the tracker will work best with a good 2-meter whip antenna, mounted high on the vehicle. And remember RF safety: while this modified rig is powered, the tracker transmits automatically and unpredictably.
Other Ideas for using APRS
If you have an android smartphone with GPS and data capabilities, and are operating with good cellphone coverage, check out the app APRSdroid, available to hams (free to manually download and install, or $5 through the Play Store). You'll need an APRS-IS passcode, which you can get instantly here. Since these apps don't tie up the ham frequencies, you can send out frequent position reports with a clear conscience. ☺