Kantronics KPC–3 Plus User Manual page 98

Advanced GPS (or APRS) Digipeating
The ―UI‖ digipeating commands described in this section add flexibility in reporting GPS
(or APRS) station positions. It is an established procedure of the reporting stations to
digipeat with generic callsigns and through a number of repeaters (e.g., ―APRS‖
repeaters). In this way, reports of their positions can reach out, via a number of
digipeaters, to any wide area. At the same time, the digipeaters supporting these
activities must establish their TNC parameters such that all UI frames ―copied‖ are
digipeated often enough (enough repeats of each frame), but not too often (too many
repeats of each frame), to achieve the desired result.
The commands introduced here (i.e., UIDIGI, UIFLOOD, UITRACE, and UIWAIT) allow
each digipeater owner a wide range of ways in which to configure their TNC (in
cooperation with other digipeaters in a network, who all need to work together) to
establish an optimum GPS (or APRS) repeating network.
Note: This section assumes you are familiar with GPS, digipeating, and APRS (each
topic is discussed elsewhere in this manual). For details about APRS (A Packet
Reporting System) developed by Bob Bruninga, WB4APR, consider obtaining a
copy of ―Getting On Track with APRS,‖ by Stan Horzepa, 157 page paperback,
published in 1996 by the ARRL, 225 Main Street, Newington, CT 06111.
Amateurs are using GPS receivers, a packet unit, and an FM transmitter to report the
location of their vehicles or stations to others. Their broadcasts use one-way (unproto
UI) packets, reporting call sign, latitude and longitude. Packet stations hearing these
broadcasts can monitor the location of the vehicles.
A common goal of these position reporting stations is to digipeat a UI packet over a
wide area (or a long distance), while moving though areas where the local callsigns may
be unknown. An effective solution for not knowing local callsigns is to establish standard
generic callsigns for digipeating stations and then use these names in digipeating paths.
Of course, this requires the acceptance and use of standards for naming and using
digipeating stations, by both the position reporting stations and the digipeating stations.
Common standards have been established by some local APRS groups, with names
such as RELAY, WIDE, and TRACE. We encourage you to contact your local GPS
(or APRS) interest group before configuring your TNC with its new digipeater
capabilities. Usage may vary by area.
Improving Efficiencies of Advanced Digipeating
As described above, mobile location reporting stations are using digipeating paths
containing generic digipeating names (e.g., RELAY, WIDE, TRACE) to extend their
range of reporting. Using generic digipeating enables a mobile station to use the same
digipeating path as it moves around, since there will (presumably) always be nearby
GPS (or APRS) digipeating stations with one or more of these generic names to pick up
transmissions (i.e., UI packets) and re-transmit them to a wider area.
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