Kenwood TH-D72A/E - Manual (Page 12)

4 CONTENTS TH-D72A/E
2 HOW YOU ENJOY APRS WITH TH-D72A/E
(WRITTEN BY BOB BRUNINGA, WB4APR)
APRS Overview
The TH-D72A/E APRS Handy Transceiver brings so many new capabilities and enhancements to the
portable and mobile operator, that it is hard to fully grasp the power that this brings to APRS. Besides
the built-in GPS, and significant enhancement of the capabilities and depth and breadth of APRS, the
new radio continues the evolution of the fundamental principles of APRS as a common information
resource channel for facilitating human-to-human communication on Amateur Radio. To see how
this fits in, it is first necessary to understand the history of APRS and packet radio.
Packet Radio History
The roots of the Automatic Packet Reporting System (APRS) go back to the late 1970s as the
AMRAD (Amateur Radio Research and Development) Group was excitedly beginning to experiment
with AX.25 packet radio. This was before the Internet and as we spent our free time in our shacks,
we were in fact all socially networked by the AMRAD voice repeater. All evening and weekends,
someone was working on something or developing something new and sharing the excitement with
the others. We hung onto our handy transceivers everywhere we went like kids these days hang
onto their iPads and smartphones to keep up with the excitement.
Figure 2-1 The History of APRS from VIC-20 to TH-D72A/E
Since only RTTY was legal in the USA, we developed a RTTY chat channel to augment our repeater
communications. We wanted a digital channel that worked just like a voice repeater. That is, anyone
who had info transmitted it, and everyone monitoring captured it. Advancing from RTTY, AMRAD
developed the AX.25 spec and as soon as it was legal, we were on the air as a chat group using real-
time Unconnected (UI) packet messaging. For this technical group, the only AMRAD operational event
was communications support for the annual Old Dominion 100 mile endurance run. In the mid 1980s,
the first vestige of APRS used Vic-20s and packet radio to share information on the hundreds of
runners and horses across the hundreds or so square miles over the 24-hour event. There was no
such thing as GPS. The system consisted of simply a packet channel where each checkpoint
beaconed information and objects about arrivals and then transferred object responsibility as it was
taken over by the next checkpoint. At any instant, everyone could see on their screens, a list of the
objects reported at each station and their status. New information was beaconed at a high rate for
immediate delivery but decayed rapidly to reduce channel loading so that fresh information had priority
with minimum collisions.