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© 1997 SGC Inc.
As was covered earlier, SSB is one half of the voice component of the standard AM signal. The SSB mode
is nearly always used for two-way communications across the HF spectrum. SSB is so popular because the mode
is much more efficient than any other voice mode and because the signals are narrower, so it is rarely hampered
by fading.
RTTY (Radio Teletype) RTTY (often pronounced as "ritty") is one of the earliest forms of data
communications. In this system, printed data is transmitted via a high-speed machine, rather than hand-keyed, as is
the case with CW communications. Although CW is a form of data communications, it is copied by a human
operator. Nobody can copy RTTY by ear. RTTY is a completely different world of communications from the voice
modes. To try to thoroughly cover this topic here would be somewhat like trying to cover every aspect of DOS and
Windows in one introductory book on computers. As a result, the information in the following paragraphs is only
intended to provide some basic information and to whet your interest in this branch of the technology.
In order to send and receive RTTY, you must have other equipment in addition to the standard HF
transceiver/antenna combination. Today, the most common arrangement would be to interface a personal computer
with your transceiver and purchase the appropriate demodulating/modulating software or a computer interface.
If no computer is available, then you are stuck with purchasing a modulator/demodulator (modem), a monitor,
and a printer.
The three major branches of RTTY communications are Baudot, AMTOR, and ASCII. The characters in
Baudot code are formed by blocks of five-digit binary codes and an initial arrow. There are "old-timer"amateur
radio/MARS friends who who have Baudot RTTY units from the mid-century. These hulking blocks of steel are true
mechanical wonders--something like a giant typewriter and printer combination in a desk-sized case full of gears.
The catch with Baudot code is that it directly intermeshes with these mechanical printers and it is prone to
interference--fades, static, and man-made interference, which cause errors in the received messages.
AMTOR is (simplified) RTTY Baudot code that has been modified to add various error-detection and
correction enhancements. The AMTOR system corrects data by sending it in time-delayed chunks. The transceivers
are connected to a "smart box"--a computer modulator/demodulator. Then, the transmitting station will send a block
of data and the receiving station will receive it and transmit a signal back to verify that it received the signal. If the
signals from the transmitting station are not received properly, then the receiving station will transmit a signal for
the other station to repeat that block of text. This process will continue until the entire message is sent. Technically,
SSB (SINGLE SIDEBAND)
DATA
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