<s>
Automatic	B-Application
Packet	I-Application
Reporting	I-Application
System	I-Application
(	O
APRS	O
)	O
is	O
an	O
amateur	O
radio-based	O
system	O
for	O
real	O
time	O
digital	O
communications	O
of	O
information	O
of	O
immediate	O
value	O
in	O
the	O
local	O
area	O
.	O
</s>
<s>
APRS	O
data	O
can	O
be	O
displayed	O
on	O
a	O
map	O
,	O
which	O
can	O
show	O
stations	O
,	O
objects	O
,	O
tracks	O
of	O
moving	O
objects	O
,	O
weather	O
stations	O
,	O
search	O
and	O
rescue	O
data	O
,	O
and	O
direction	B-Device
finding	I-Device
data	O
.	O
</s>
<s>
Bob	O
Bruninga	O
,	O
a	O
senior	O
research	O
engineer	O
at	O
the	O
United	O
States	O
Naval	O
Academy	O
,	O
implemented	O
the	O
earliest	O
ancestor	O
of	O
APRS	O
on	O
an	O
Apple	B-Device
II	I-Device
computer	O
in	O
1982	O
.	O
</s>
<s>
This	O
early	O
version	O
was	O
used	O
to	O
map	O
high	B-Algorithm
frequency	I-Algorithm
Navy	O
position	O
reports	O
.	O
</s>
<s>
The	O
first	O
use	O
of	O
APRS	O
was	O
in	O
1984	O
,	O
when	O
Bruninga	O
developed	O
a	O
more	O
advanced	O
version	O
on	O
a	O
VIC-20	B-Device
for	O
reporting	O
the	O
position	O
and	O
status	O
of	O
horses	O
in	O
a	O
endurance	O
run	O
.	O
</s>
<s>
Following	O
a	O
series	O
of	O
Federal	O
Emergency	O
Management	O
Agency	O
(	O
FEMA	O
)	O
exercises	O
using	O
CETS	O
,	O
the	O
system	O
was	O
ported	O
to	O
the	O
IBM	B-Device
Personal	I-Device
Computer	I-Device
.	O
</s>
<s>
During	O
the	O
early	O
1990s	O
,	O
CETS	O
(	O
then	O
known	O
as	O
the	O
Automatic	B-Application
Position	I-Application
Reporting	I-Application
System	I-Application
)	O
continued	O
to	O
evolve	O
into	O
its	O
current	O
form	O
.	O
</s>
<s>
APRS	O
(	O
Automatic	B-Application
Packet	I-Application
Reporting	I-Application
System	I-Application
)	O
,	O
is	O
a	O
digital	O
communications	O
protocol	O
for	O
exchanging	O
information	O
among	O
a	O
large	O
number	O
of	O
stations	O
covering	O
a	O
large	O
(	O
local	O
)	O
area	O
,	O
often	O
referred	O
to	O
as	O
"	O
IP-ers	O
"	O
.	O
</s>
<s>
As	O
a	O
multi-user	O
data	O
network	O
,	O
it	O
is	O
quite	O
different	O
from	O
conventional	O
packet	B-Application
radio	I-Application
.	O
</s>
<s>
Rather	O
than	O
using	O
connected	O
data	O
streams	O
where	O
stations	O
connect	O
to	O
each	O
other	O
and	O
packets	O
are	O
acknowledged	O
and	O
retransmitted	O
if	O
lost	O
,	O
APRS	O
operates	O
entirely	O
in	O
an	O
unconnected	O
broadcast	O
fashion	O
,	O
using	O
unnumbered	O
AX.25	B-Protocol
frames	O
.	O
</s>
<s>
Packet	O
repeaters	O
,	O
called	O
digipeaters	O
,	O
form	O
the	O
backbone	O
of	O
the	O
APRS	O
system	O
,	O
and	O
use	O
store	B-Protocol
and	I-Protocol
forward	I-Protocol
technology	O
to	O
retransmit	O
packets	O
.	O
</s>
<s>
In	O
addition	O
to	O
real-time	O
position	O
reporting	O
capabilities	O
using	O
attached	O
GPS	O
receivers	O
,	O
APRS	O
is	O
also	O
capable	O
of	O
transmitting	O
a	O
wide	O
variety	O
of	O
data	O
,	O
including	O
weather	O
reports	O
,	O
short	O
text	O
messages	O
,	O
radio	B-Device
direction	I-Device
finding	I-Device
bearings	O
,	O
telemetry	O
data	O
,	O
short	O
e-mail	O
messages	O
(	O
send	O
only	O
)	O
and	O
storm	O
forecasts	O
.	O
</s>
<s>
In	O
its	O
most	O
widely	O
used	O
form	O
,	O
APRS	O
is	O
transported	O
over	O
the	O
AX.25	B-Protocol
protocol	O
using	O
1,200	O
-bit/s	O
Bell	B-Device
202	I-Device
AFSK	O
on	O
frequencies	O
located	O
within	O
the	O
2-meter	B-Algorithm
amateur	I-Algorithm
band	I-Algorithm
.	O
</s>
<s>
A	O
number	O
of	O
low-Earth	O
orbiting	O
satellites	B-Application
,	O
including	O
the	O
International	O
Space	O
Station	O
,	O
are	O
capable	O
of	O
relaying	O
APRS	O
data	O
.	O
</s>
<s>
An	O
APRS	O
infrastructure	O
comprises	O
a	O
variety	O
of	O
Terminal	B-Protocol
Node	I-Protocol
Controller	I-Protocol
(	O
TNC	O
)	O
equipment	O
put	O
in	O
place	O
by	O
individual	O
amateur	O
radio	O
operators	O
.	O
</s>
<s>
PropNET	O
uses	O
the	O
APRS	O
protocol	O
over	O
AX.25	B-Protocol
and	O
PSK31	B-Device
to	O
study	O
radio	O
frequency	O
propagation	O
.	O
</s>
