Digital Modes
Exchanging text, email, graphics, and files is an important part of
today's emcomm and other applications of radio. The modes that transmit
and receive data are referred to as digital modes. On VHF and UHF, the
most common digital mode is packet radio or "packet".
(tapr.org/packetradio.html)
The name comes from data being transmitted in groups of characters that
are called packets. Packet is also known as AX.25, the designator of
the technical standard that describes it. To use packet, you'll need
an FM radio, a special interface called a terminal node controller (TNC),
and a computer as shown in Figure 6. Some radios have TNCs built in.
Packet provides "keyboard-to-keyboard" communication a bit like instant
messaging. It is also used to send email from your computer via Winlink
system mailboxes.
The Automatic Position Reporting System (APRS -www.aprs.org) uses packet
radio to report your position and other information over the Internet.
A few radios have features designed for use with APRS, such as special
text displays, a data interface to communicate with a GPS receiver, or
built-in GPS receivers.
Packet commonly operates at two speeds; 1200 bits/second (bps) and 9600
bps (about 120 and 960 characters/second, respectively). At the slower
speed, the TNC converts characters from the computer's serial or USB port
into audio tones fed to the radioÆs microphone input. Any FM voice radio
is suitable for packet radio use at 1200 bps.
To operate at the higher data rate, the radio must have a special
connection specifically for use with digital modes. 9600 bps is more
demanding of the radio and not all radios work well at that speed.
Check the radio's specifications to see if it is rated for 9600 bps
data. Unless you specifically need to use high-speed data communication,
you don't need 9600 bps capability. Most packet operation takes place at
1200 bps.
D-STAR is a new digital data system based on a standard from Japan.
Equipment is currently available from Icom
(icomamerica.com/en/products/amateur/dstar) along with some third-party
adapters.
D-STAR radios can talk directly to each other or through networks of
repeaters linked over the Internet. On 2 meters and 70 cm, D-STAR radios provide
a low-speed data connection (about 80 bps) directly from the
radio to your computer's USB or serial port; no TNC is required. On
1.2 GHz, D-STAR radios provide a network-style Ethernet connection to
your computer, compatible with Web browsing and other Internet
applications. The speed is about the same as the fastest 56 kbps dial-up
connections.
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* Origin: The Thunderbolt BBS - wx1der.dyndns.org (57:57/10)
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