KJ1H-9: APRS Motorcycle Mobile

What is APRS?

As defined on Wikipedia:

Automatic Packet Reporting System (APRS) is an amateur radio-based system for real time tactical digital communications of information of immediate value in the local area.[1] In addition, all such data is ingested into the APRS Internet System (APRS-IS) and distributed globally for ubiquitous and immediate access. Along with messages, alerts, announcements and bulletins, the most visible aspect of APRS is its map display. Anyone may place any object or information on his or her map, and it is distributed to all maps of all users in the local RF network or monitoring the area via the Internet. Any station, radio or object that has an attached GPS is automatically tracked. Other prominent map features are weather stations, alerts and objects and other map-related amateur radio volunteer activities including Search and Rescue and signal direction finding.

APRS has been developed since the late 1980s by Bob Bruninga, callsign WB4APR, currently a senior research engineer at the United States Naval Academy. He still maintains the main APRS website. The acronym “APRS” was derived from his callsign.

Why use APRS?

I’ve been a ham radio operator since 1989.  On my Silverwing, I was inspired to set up a motorcycle mobile station, with a headset in my helmet, so that I could chat on the air as I rode. As soon as I put the finishing touches on this system, I realized that I didn’t like the distraction, and preferred to just ride instead. But since I’d already set the bike up with a radio and antenna, it wasn’t much of a leap to plug something other than a headset into it, such as APRS equipment.

During my bike trips, I often go in and out of cell phone coverage. In the event of an emergency in a remote area, I’d still like to be able to call for help, and having a ham radio on board is ideal for that. In addition, by having an APRS station, people watching my progress on the radio or the internet may well have a better idea where I am than I do.  It’s a bit of a safety net.  If friends and readers like you are watching my progress, and I don’t report in from my intended destination, the alarm bells go off and people know to send help.

I hope it never has to be used in that way, so the primary goals of my motorcycle APRS station are to automatically map my rides for my own reference (I might want to revisit that fun, twisty road I accidentally found), and for the entertainment of fellow hams and readers like you. All you have to do is go to APRS.FI, search for KJ1H-9, and there I am. And because this information goes out to the internet, anyone can see it – no amateur radio license required.

How did I do it?

20120707-193742.jpgMy APRS station has evolved through trial and error into its current form. Ironically, although I started playing with APRS because it utilized a lot of equipment I already had, it now only uses a couple of parts of the original setup. Yet it’s still not a dedicated APRS station. I can still plug in a microphone and chat with people by voice, or remove the radio from the bike entirely if I need it elsewhere.

Originally I used a Radio Shack HTX-202 handheld radio. I powered it from the switched power lead for the stereo my Silverwing didn’t have, which let it put out 5-6 watts on high power.  The antenna is a 1/2 wave for the two meter band (the national APRS frequency in the U.S. is 144.390 MHz).  I used this instead of the more traditional 1/4 or 5/8 wave antennas because those require a flat metal groundplane for the best operation, and a motorcycle provides a very poor groundplane.  The 1/2 wave does not require a groundplane at all.  I attached it to the chrome bars for the bike’s trunk with a clamp mount intended for a big rig’s mirror.  It worked great.

IMG_0129I set all this up for voice operation using a headset in my helmet and a push-to-talk button on the handlebars. When I decided to do APRS instead, I picked up a TinyTrak3+ and the wiring harness to connect it to my HTX-202 from Byonics. I had some problems getting it to work at first, and Byon was a great help in eventually figuring out that I had a bad wiring harness, which he promptly replaced. It was easy to program, and I was soon on the air.

Sort of. I used it extensively during my local rides as well as my Vermont trip of 2012, but I would often go for hours without a single position report being heard.  It rather defeated the purpose of having the system in the first place, so I didn’t use it for a long time. I thought about picking up a mobile radio with higher power output, but the difficulty of mounting it in a removable trunk or saddlebag steered me away from that idea.

Then I picked up my PC800. It has a lot more cargo space than the Silverwing, which meant it was easier to spare the room a mobile radio would take up. Its “saddlebags” are actually a large trunk area integrated into the back of the bike, which meant that all of the wiring could be run internally. I’d bought a Kenwood TM-281A two meter mobile radio for a number of purposes. After moving, I found that I could hit all of the local repeaters I wanted to with my handheld radio and didn’t need the more powerful mobile radio at my home, so I decided it was time to revisit the motorcycle APRS idea.

IMG_0594The logical place to install the radio was in the forward portion of the right side of the trunk. The battery is just in front of this area, so it was a short and easy run.  I screwed the factory bracket for the radio into the side of the trunk, then bolted the radio in. It’s solid.  Then I used some “Superlock Fasteners” from Radio Shack (it’s the same sort of Velcro type stuff an EZ Pass mounts to your windshield with) to stick the TinyTrak3+ to the side of the trunk near the radio.  I bought two additional wiring harnesses from Byonics. One of them lets me plug the TinyTrak3+ into a Kenwood mobile rig. The wires aren’t too long, but they’re just long enough for me to plug them into the microphone and earphone jacks, and I can still see the lights to verify that it’s working correctly. The other wiring harness I picked up plugs in between the power cord to the battery and the power lead from the radio itself, and adds a PowerPole connector.  This is how I power the TinyTrak3+ rather than the cigarette lighter adapter, which is all the way at the other end of the bike. Everything is mounted securely and powered adequately. I also had to make a minor modification to the TinyTrak3+ by cutting a resistor (R8) so that it will work with a mobile radio rather than a handheld. This easy mod is clearly described in the documentation and was no trouble at all.

IMG_0593

I still had to figure out how to install the antenna. The PC800 didn’t have anywhere I could clamp my existing mount onto that wouldn’t get in the way. After searching for a mount that would work, I ended up making my own. I replaced one of the bolts for my Givi top trunk rack with one that is identical except longer, and then bolted a metal bar onto it with a 90 degree bend. A Hustler NMO mount bolts through a 3/8″ hole in the bracket.  I made it long enough to ensure that it stuck out far enough for the antenna to clear the top trunk, and this provided enough room to stick the GPS antenna to the same bracket. This was also useful because of the antenna’s magnetic base, since the entire outside of the bike is plastic. The bracket vibrates a bit as I ride down the road, and I may reinforce it at some point, but it’s perfectly adequate for now. The zip ties are to keep the wires in place, not the antennas themselves. The wires run under the passenger seat attached to the top of the trunk lid, along the supporting frame, and directly down to the radio and TinyTrak3+.

aprsThe Kenwood TM-281A transmits 65 watts on the high power setting, over 10 times as much power as the HTX-202. This seems to be what I needed to get my signal out to local APRS stations adequately. This map is a screen capture of one of the first rides I took after installing the APRS station on the PC800. Each dark red dot corresponds to my automatic position reports. The line connects the dots between them so you can see my approximate route.  The more dots, the more accurate the mapping.  Although on this ride none of my reports were heard between Harvard and Groton, you can still get the basic idea of my route, and can guess that I took Route 111 through there. As I got close to some other APRS stations, the map got more precise, as you can see around the Chelmsford area when I went literally right past the home of KB1UTS, and again in Acton when I was near W1JMC. Previously only a few position reports would ever make it to the map, and my route would not be recorded. The extra power of the TM-281A makes the difference.

Some have noted that Kenwood warns against using the high power setting very much due to overheating concerns. Additionally, the bike trunk is a fairly small, enclosed space, and when I go on longer trips I will be packing stuff all around the radio, further reducing ventilation. However, the nature of an APRS station is to transmit a data burst of about one second every few minutes. The radio doesn’t use much power when it’s receiving, and it’s transmitting for too short a time to generate any significant heat. I don’t expect this to be a problem. However, when I plug in a microphone to make voice contacts while parked, I will make sure to switch to the lower 25 watt power setting.

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