APRS
Automatic Position Reporting System. A service based on Packet Radio.
Inhaltsverzeichnis
1 My Site
Have a look here:
2 Involved Hardware
In order to generate APRS packets:
- You generally have a GPS receiver
- and a little Terminal Node Controller (TNC) which encodes the NMEA data from the GPS receiver in the AX.25 data format and makes sure the channel is not busy. If the channel is free, the TNC sends the packet to the radio.
- In Europe, the APRS frequency is generally 144.800 MHz. So you need a 2m VHF radio.
There are also handheld and mobile transceivers on sale which have a TNC built in. There are also tracker devices around which substitute the TNC and are much smaller. Anyway, there are all sorts of products meanwhile...
On the other side, someone needs to receive these packets. So there again, you need
- a radio for 144.800 MHz,
- a TNC to decode the packets. It's noteworthy that most TNCs are operated in the KISS mode which loads all the data processing on the computer residing behind.
- a computer which processes the packets. They can either be projected onto a map locally or they can be forwarded through the internet to aprs.fi where they are projected into a Google map. So you can eventually track an APRS station on a map.
In case there is no internet-connected station nearby, APRS stations may also act as relays. This means that an APRS station receives a packet and assumes that it must forward it. So the packet will be re-broadcasted again in the hope that there is another station around that is able to forward it to the internet. This practice is causing quite some traffic.
Here's some information ont the KF-163
3 Involved Software
I will just consider OpenWRT software since I am firmly convinced that high-power computers are massively undercharged by the task of forwarding packets that come in by 1200 bit / second.
- aprx - a receiving only APRS forwarder
- aprs4r - a fully fledged APRS digipeater
