APRS
APRS is a packet radio (AX.25) based system for passing messages, many of which are position reports (from a GPS receiver). I’ve been playing with APRS for a little while and find that it is an interesting way of looking at propagation and just to tinker with radio data.
A good wrap of APRS in Australia is at www.aprs.net.au, with specific Queensland details available.
I use an OpenTracker1+, from Argent Data Systems, as my portable tracker. This device is fairly simple and interfaces easily to my handheld radios. Unlike some of the other small trackers, this one can receive position reports and from them generate NMEA waypoint messages for feeding back to a GPS. I’ve interfaced the OT1+ with my Garmin Geko 201, and the Geko will show the received callsign and put a waypoint on the screen showing the location. As hams move around the waypoint is updated. Unfortunately the screen on the Geko is a bit small, but with a larger GPS this provides a useful display. For the sake of compactness I use a Deluo GPS ‘mouse’ to provide position info. The OT1+ is currently configured as VK4TDI-9.
I’ve ordered a Tracker2 from Argent to use as a digipeater at home. This will be VK4TDI-1 and will replace my existing setup where I’ve interfaced my FT-8800 to a PC running UI-View. The PC arrangement used too much power, tied up my radio and wasn’t something I’d leave on the whole time. A standalone device, hooked into my spare FT-1802 running off a big gel cell will provide fill-in coverage for the inner western suburbs (Indooroopilly to Toowong) area, which is a bit of a blackspot for VK4RBR-3 at Mt Gravatt.
My weather station software, WxService, has APRS capability sending a weather report through the Australian APRS gateways with a fixed location. Since this computer is not connected to the internet, it is setup as VK4TDI-10 (it was VK4TDI, but that clashes with DPRS position reports via D-STAR), with updates every 15 minutes. I’ve changed the default APRS servers to first.aprs.net.au & second.aprs.net.au to make the system more reliable (connections to the US were timing out).
D-STAR has the capability of sending position information during each voice transmission as background data, or it can send a short transmission which is only the position. This system is called D-PRS, and the gateway computer at VK4RWN (Springbrook) converts the Lat/Long info from the D-Star transmission and sends to to the APRS system. This is a great linking system and means that people with analogue radio running AX.25 based APRS can still see positions from people with D-Star. The SSID on a D-Star report is alpha rather than numeric, such as P or M, so this might confuse some ‘over the air’ APRS receivers.
