Kantronics KPC–3 Plus User Manual
Also see for KPC-3 Plus: User guideUser guideManual
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91GPS NMEA InterfacingMost Kantronics‘ TNCs, e.g. KPC-3 Plus, KPC-9612 Plus, KAM XL, and others, supportthe GPS mode, explained below. Each contains firmware to interface with a GPS devicesupporting the NMEA 0183 interface standard; commands to configure and controlunproto (path) retransmissions of the NMEA strings, and provides RAM storage forlocation messages (strings) for later retrieval.Among Kantronics‘ TNCs supporting GPS, the only difference between devices isthe number of radio ports available for transmission of data. For example, the KPC-3Plus is a single port device and the KPC 9612 Plus is a multi-port device.OverviewThe Global Positioning System (GPS) was developed initially for military use by the U.S.Department of Defense, to provide worldwide positioning and navigational informationfor U.S. military forces. Since then, a broad range of commercial, civilian, and amateurradio applications have been developed, based on the GPS. The GPS consists of 24satellites, each of which transmits positioning information continuously. GPS receivingunits - devices that contain a receiver, LCD screen, and (usually) a data port - collectthis positional information and use it to compute position. This information can then beretransmitted by any means possible to report the position of the GPS unit (and itsvehicle).Most GPS units sold today are NMEA compatible. That means that not only can theydisplay latitude, longitude, and time on a LCD screen, but the information can bepresented to your computer or TNC via the GPS unit‘s serial data port. The informationis presented in ASCII in the form of NMEA ―sentences‖. A number of these sentencesare available —with varying kinds of information, but the one used most often foramateur radio activities is ―$GPGGA‖. This sentence contains latitude, longitude,altitude, and time (in UTC, derived from the satellite clocks). The TNC, in GPS Mode,can receive and retransmit this information as beacons and/or store these sentences ina large tracking buffer for later retrieval. The TNC, in GPS Mode, also updates its clockto UTC, derived from the satellites. Hence, the location of your remote packet station,recorded at a specific time, can be tracked by other packet stations.Amateurs the world over have discovered GPS and are combining this exciting newtechnology with packet radio for reporting the position of their vehicles, following balloonlaunches, finding hidden transmitters, and determining location information for moreserious applications as well. A typical amateur location reporting system consists ofGPS-packet equipped vehicles and fixed-location packet repeaters. At a minimum, eachvehicle would carry a GPS receiver, a packet unit (TNC), and a transmitter. Each TNC,in GPS mode, would be set to beacon location periodically. The fixed-locationdigipeaters would relay the reporting stations‘ locations over a wide area. For moredetails on setting up such a system, see the next section, on ―Advanced Digipeating.‖ |
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