DIGITAL MODES: the new
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HF Packet |
Packet
Radio: What? Why? How?
HF Packet uses the standard AX.25 protocol
same as for VHF Packet. It is run at a fixed
300 baud rate for HF. Data is arranged in
packets of up to 256 bytes of 8 bit ASCII
data. Each packet contains a 1 byte start
flag, 3 byte address field, 1 byte control
field, 0-256 bytes of data, 2 byte CRC and
finally a 1 byte end flag. Packets are
transmitted with no fixed timing. See the
latest specification published by the
American Radio Relay League (ARRL) for
complete details on this system. There is
also some 1200 baud PSK work done in the 10
meter ham band.
Automatic Packet Reporting System or APRS,
is an application that runs "on top of" AX.25.
It was invented by Bob Bruninga WA4APR (clever
call letters) that utilizes GPS data to plot
a packet station's location on a map of a
given region, city, state, or even country.
Due to the graphics involved, some units may
not read this data; however, units like the
PK232 can read it with the use of special
software. Signals utilizing this mode are
found in the 40 and 30 meter bands (for
example) utilizing 'gateways' into 2 meters.
Packet radio has been around since the
mid-1960's, but was first seen on the
amateur bands in 1978 through research done
in Montreal, Canada in 1978, the first
transmission occurring on May 31st. This was
followed by the Vancouver Amateur Digital
Communication Group (VADCG) development of a
Terminal Node Controller (TNC), also known
as the VADCG board, in 1980. This was then
followed by TAPR (Tucson Amateur Packet
Radio) with the creation of the TNC-1 in
1982 and then the TNC-2 in '84-'85. Ten
years ago, the packet radio revolution
ignited when TAPR sold over a thousand TNC-2
kits. The TNC-2 was what was needed to make
this mode, that a few experimenters were
playing with, into something that every
amateur could enjoy. From its humble
beginnings, where it was good luck to have
more than three packet operators in the same
city, packet radio now has thousands of
amateurs using it daily, various
manufacturers making and selling TNCs
(terminal Node Controllers), and over a
hundred thousand TNCs having been sold to
date. What growth! No other mode of amateur
radio has seen such explosive growth!
Like the title says, 'Why Packet Radio ?'
Like any mode in the amateur service, it
provides a group of amateurs with a way of
having fun and meeting one of our primary
aims, 'improving the radio art.' Packet
radio was a new mode in the early 80's that
many of the outstanding amateur
experimenters worked on and developed. The
result, ten years later, is something that
provides a lot of different operating
opportunities. No longer is it just packet
radio, but now it is bulletin board systems,
DX Clusters, chat bridges, networking,
emergency communications, satellite
operations and much more. But what are these
? and is one of these, something that you
want to do? How do you know? Let's start off
with a basic question.
Packet Bulletin Board Systems (BBS):
Most cities have one or more packet Bulletin
Board Systems, or BBS for short. BBSs do two
main things: send and receive personal
messages for their local users (like
yourself) and send and receive messages or
bulletins intended for people locally or
around the world. Since the BBS is part of a
national system of other BBSs, it has the
ability to pass information or messages to
any other BBS in the US or the world. This
allows you to send messages to friends
locally, to someone located in the next
state, or to someone on the other side of
the world. The second thing that BBSs do is
pass local and national bulletins, which are
messages intended to be read by everyone. In
this way, amateurs can read the latest
messages about the ARRL, AMSAT, TAPR,
propagation, DX, and other bulletins on
varied topics. Message passing is the
primary purpose of a BBS system, but BBSs
can also support callbook programs, help
references, Internet access, and more.
Operators of BBS systems are a good place to
start when you first get on the air. Because
of the service they provide, they have to
know how packet is working in the local
area.
Keyboard-to-Keyboard:
Like other amateur modes (SSB, FM, etc),
packet radio can be used to talk to other
amateurs directly. Amateurs can talk to each
other simultaneously using their keyboards
when they can directly communicate with each
other. With the use of networks (see a
little later), amateurs can talk at a
distance beyond the reach of their own
stations by using the network.
Keyboard-to-keyboard communications is one
of the least frequent methods of packet
communications, because amateurs are rarely
on packet at the same time. Many packet
operators send electronic mail using either
personal mailboxes or a local BBS. In this
way, messages are read when the amateur is
on the air. Another limitation to direct
keyboard-to-keyboard packet is that you can
only talk to one packet station at a time Q
no easy way to hold round-table discussions
like on a voice repeater. Some areas support
chat or conference bridges, which allow for
more than one amateur to talk to each other
Q much like a voice repeater. If a chat is
supported over a network, then you can talk
to someone as far away as the network
reaches.
DX Packet Cluster:
Many cities have DX (foreign amateur)
spotting nodes or networks. HF (High-Frequency)
operators connect to their local DX Packet
Cluster in order to receive reports on the
latest DX. This type of packet came about
from those interested in 'chasing' DX. Many
amateurs like to frequent the HF bands
looking for rare international operators to
contact. A DX Cluster allows many HF
operators to be connected over packet radio
at the same time while operating HF and
hunting for DX. When someone finds a DX
station, they send a packet message to the
DX Cluster, which then sends the information
to all other packet operators using the DX
Cluster. In this way, you have several
stations monitoring the band, looking for DX.
Often an amateur will 'spot' (hear) a DX
station and then distribute the DX report
almost instantly. DX Clusters allow everyone
to operate many more hard to find DX
stations in one evening than was possible
operating by oneself. Some amateurs have
been known to attain enough contacts to
qualify for DXCC in a matter of weeks. One
point though, if your HF station is not a 'big-gun',
then it is sometimes best to operate the DX
station before posting your spot for others
to find. There is a good chance that a
pile-up will occur as soon as you make your
spot to the DX Cluster and then you will not
be able to work the DX station that you
found!
RACES/ARES/NTS and Emergency Communications:
Packet radio is being used in many emergency
services. Whether packet is used to pass a
message accurately and in large quantities
or to handle messages passed by the National
Traffic System, it can provide an important
function like any other amateur mode when
used correctly. A new application called
APRS combines GPS (Global Positioning
Satellites) with packet radio to allow a
master station to plot on their computer the
location of all other stations in the field.
The purpose is to coordinate the exact
position of weather spotters or searchers,
without having to waste radio time informing
the control station of their locations.
Recently, amateurs in Oklahoma have been
distributing Doppler Radar images via the
packet network. The small weather image file
takes but a few minutes to retrieve and
display. This helps those amateurs outside
of the local ATV coverage to get an accurate
weather picture from the Doppler Radar.
Networking:
Since amateurs use radios to transmit their
data, their range of communications is
limited to approximately line of sight. An
average packet station talks in a radius of
about 10-30 miles. Packet Networks allow
amateurs to widen the area of communications
past their line of sight, by having a series
of packet stations linked by radio, that can
be used to get their packet messages to
where ever the network goes. Much like the
telephone system, networks provide long
distance service outside the local area.
There are a number of amateur networks which
allow amateurs to travel from one area to
another. Network types include:
Net/Rom, TCP/IP, TexNet, G8BPQ, ROSE,
KaNodes, and many more.
These networks are typically built by a
local or regional group that allows packet
operators to get outside of their area.
Amateurs get hooked on building and
maintaining such networks, just like some
amateurs operate DX or handle emergency
communications. The type of network you use
locally will depend on your area. Much
depends on the network philosophy the local
group has chosen when developing their
network.
Satellite Communications:
Many of the amateur radio satellites in
orbit contain computer systems that provide
packet capability. Most packet satellites
provide BBS-like functions for messages to
be passed to anywhere in the world within 24
hours. Several contain CCD cameras, which
allow amateurs to download images of the
earth and some allow users to retrieve data
from the onboard experiments. Most
satellites use AX.25 with special software
developed for satellite communications.
DOVE, Digital Orbit Voice Encoder, can be
received with any normal VHF/FM 2-meter
packet station, but most of the packet
satellites use SSB and require more complex
equipment in order to operate them. Just
something else to spend your amateur dollars
on.
Conclusion:
These are just some of the things you can do
with packet radio. Once you find something
that you can do with packet radio, then you
have a reason to purchase the equipment
necessary to get on the air. A good place to
start is to find a friend who uses packet
and go visit. See what your local area has
to offer. As already stated, packet radio
changes every 50-miles. What is being done
where I operate is probably slightly
different than what you can do where you
live. |
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