A GPS Tracking Gizmo for APRS

APRS is a system that allows equipped stations to see where other equipped stations are by use of GPS. The normal setup would require a computer, radio, TNC and a GPS receiver. This is fine for the house or portable location but how does one fair with all this equipment when mobile. Worse still, its almost impossible to carry all that stuff when you're on foot!

So I set about trying to find ways of making it lighter and easier to carry. I get about the city quite a bit in the summer months doing things for the big events like the New York City Marathon. It would be useful, I thought, for the net control stations to know where I am as I often end up on buses and vans being taken somewhere whilst following the event in keeping with my ARES activities.

The picture on the left is of a MIM module. Basically its a modem with intelligence. It listens to a GPS signal fed to it via its serial port and then at a pre determined time formats a packet of APRS data and transmits it via an attached radio. It's shown next to a US 'Quarter' (25c for the non Americans) so you can appreciate how small it is.

I mounted this inside an 'Infra Red' project box from radio shack and attached a belt clip to it so that it could sit on my belt next to my radio. The GPS receiver was plugged into the top and then placed onto the headband of my speaker/mic headphones.

The picture on the right demonstrates how the GPS receiver and the radio antenna were attached to the headset. The antenna lives just behind my left ear and is attached to the speaker cup with a slightly modified MFJ 'HatTenna' clip. The HatTenna normall clips onto the visor of a baseball cap or other head dress by means of a clip that is screwed onto the side of the device. I removed the screws and using the clip as a drilling template sank 2 holes into the speaker cup. The screws were then resude to hold the remaining part of the HatTenna in place. This mounting has proven to be very sturdy. I have cought the antenna on doorways and tree's etc many times and it has always remained fast.

The GPS receiver is mounted on the headband using some black plastic 'zip ties'. As I didn't want the GPS to be a permanent fixture I chose the zip ties for their ease of use and removal.

The original plan was to use the APRS system on the same channel as I was talking on with the same radio equipment. This would mean that the people listening would have to tollerate a short burst of data every few minutes or so at the end of my transmission. This turned out to be ok on the one occasion I actually used it. Since building the 'Man Portable APRS' as it became know its been lying in a box unused.

Maybe I'll get up some energy one day and revamp the design. I'll, post more pictures of the finished article when I next get my camera out.