Overview of Modes of Digital Communication
HF/VHF and Packet/Non-Packet Communication
Historically, digital modes found their way into radio communications in the HF
bands (3 to 30 Mhz) first. Morse Code (CW) was, of course, the first digital
mode! Radio teletype (radio telex) followed, in the 1950s, as teletype machines
became plentiful. Teletype Over Radio (TOR) followed quickly thereafter, and
was the first mode to use error detection, and was quickly adopted by commercial
services.
Radio amateurs adopted TOR in the late 1970s and called it AMTOR. Computer
networking protocols used in early government computer networks such as
ARPANET - forerunner of the INTERNET - eventually found their way into ra-
dio communications too in the form of packet radio. Radio amateurs modified the
X.25 protocol, called is AX.25, and adapted it for both HF and VHF packet ra-
dio communications.
Radio modems, of course, have evolved along with these introductions. The first
radio modems were called terminal units and did nothing but interface a teletype
machine (or computer operating as a dumb terminal) and an HF radio. In the late
1970s home computing began to emerge and many small computers were intro-
duced: the TRS-80, the ATARI, the TI-99, the VIC-20, and the Commodore-64.
As you might expect, those of us writing programs for those computers to do ra-
dio teletype and CW got a bit cranky each time a new machine came out! Our so
-
lution was to push the programs to decode radio teletype, CW, and later packet
inside the terminal unit. This was possible only because the microprocessor had
appeared on the scene. By pushing the code inside the terminal unit - and calling
it a Universal Terminal Unit - we avoided having to write code as the Apple and
PC began popular.
Today, smart terminal units are called terminal node controllers (TNCs). The
KAM’98 is the latest in the evolutionary chain. The KAM’98 is still an interface
between your PC and your radio but it does all the work of coding and decoding
the various communication modes used today: CW, RTTY, ASCII, AMTOR,
Pactor, G-TOR, and more.
Introduction Overview of Modes of Digital
User’s Guide 22 KAM’98 v 8.3
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