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GPS NMEA Interfacing Capability
Most Kantronics TNCs, e.g. KPC-3 Plus, KPC-9612 Plus, KAM Plus, and others,
support the GPS mode, explained below. Each contains firmware to interface
with a GPS device supporting the NEMA-0183 interface standard; commands to
configure and control unproto (path) retransmissions of the NEMA strings, and
provides RAM storage for location messages (strings) for later retrieval.
+ Among Kantronics’ TNCs supporting GPS, the only difference between devices
is the number of radio ports available for transmission of data. For example, the
KPC-3 Plus is a single port device and the KPC 9612 Plus is a multi-port device.
Overview
The Global Positioning System (GPS) was developed initially for military use by
the U.S. Department of Defense, to provide worldwide positioning and naviga-
tional information for U.S. military forces. Since then, a broad range of commer-
cial, civilian, and amateur radio applications have been developed, based on the
GPS. The GPS consists of 24 satellites each of which transmits positioning in-
formation continuously. GPS receiving units - devices that contain a receiver,
LCD display, and (usually) a data port - collect this positional information and
use it to compute position. This information can then be retransmitted by any
means possible to report the position of the GPS unit (and its vehicle).
Most GPS units sold today are NMEA compatible. That means that not only can
they display latitude, longitude, and time on an LCD screen, but the information
can be presented to your computer or TNC via the GPS unit’s serial data port.
The information is presented in ASCII in the form of NMEA “sentences”. A
number of these sentences are available — with varying kinds of information, but
the one used most often for amateur 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 in a large tracking buffer for later retrieval.
The TNC, in GPS Mode, also updates its clock to UTC, derived from the satel-
lites. 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
new technology with packet radio for reporting the position of their vehicles, fol-
Modes of Operation GPS NMEA Interfacing Capability
User’s Guide 160 KPC-9612 Plus v 8.2