22 May 2017
THE HAM‘S WIRELESS WORKBENCH n BY WARD SILVER N0AX
Ham Radio Data Modes
The original modes used by hams were intended for
“human copy” in that the information was meant to be
understood by a human listening to the receiver’s audio
output. Even the initial “spark” (imagine turning a Tesla
coil on and off with a Morse code key and you get the
idea) was received by ear. The spark was “chopped” by a
rotating wheel with contacts on it. Turning the spark on
and off at a rate in the low audio range (less than 1,000
Hz) made the hiss of the radio spark audible as a tone.
Human copy was the norm as CW (from “continuous
wave”) displaced spark. Then, the voice modes of AM, FM,
and SSB (see the previous column) were introduced. Most
ham radio is conducted by one of these modes even today.
However, the times, they are a-changin’.
Digital modes — according to the Federal
Communications Commission (FCC) — are those that
exchange information as characters. More accurately, the
FCC distinguishes between data modes and radioteletype,
or RTTY (pronounced “ritty” by hams; see en.wikipedia.
org/wiki/Radioteletype). In data modes, characters are
exchanged by computers (including microprocessors or
other digital gadgets) and might represent a file, a message,
telemetry, command characters, or something similar.
RTTY, on the other hand, is a special data mode — the
RTTY, Our Digital Ancestor
RTTY is formally defined as direct-printing telegraphy
because of its origins as an electro-mechanical system that
connected keyboard-like contraptions over a telephone line
or radio link. The bits of each character are encoded as a
pair of tones for transmission. The receiver audio is then
turned into printed characters by the teleprinter. (There’s
more to it, but a complete explanation would take at least
one whole article!) Teletype — now a generic term for the
mode — was actually the name of the Teletype Corporation
The first working teleprinter was developed in 1908,
but the radioteletype system really came into wide use
in the 1930s. Without making this in to too much of a
history lesson, the Teletype Model 15 was the PC of its
day. Its maze of solenoids and levers was the pre-electronic
equivalent of a UART and terminal. If you’ve ever seen
one running, it’s unforgettable. “How the Teleprinter
Works” is a 1940 tutorial about these mechanical marvels
( www.youtube.com/watch?v=HcMHam54EOI) and a
video of a working Model 15 that was in service for more
than 50 years can be seen online at www.youtube.com/
watch?v=Ml00ngVwrcU. There is something very cool
about watching a teleprinter over the Internet!
Many terms used in digital communications today
— baud, mark, and space are just a few — came from the
world of radioteletype. Baud (the number of symbols
transmitted per second) is named for Baudot, who invented
the five-bit code used to encode characters. Mark and
space refer to the bits of the code. Start and stop were the
synchronization intervals between characters, and so forth.
RTTY was the direct precursor to all of today’s
digital communications and many veteran programmers
used teleprinters — particularly the Model ASR 33 — to
communicate with mainframes “back in the day.” Hams
adapted surplus teleprinters to deploy amateur radio’s first
digital mode in the post-WWII era. The mechanical units
were eventually replaced with electronic display terminals,
then microprocessor based systems, and finally the PC and
sound card to send and receive the world’s oldest digital
RTTY may not be the most robust in terms of error
rate and it’s certainly not the fastest, but it’s simple and
easy. Anyone can listen into the conversation and it doesn’t
require special or proprietary equipment. RTTY is closing in
More modes, baby! Live listening, too!
Wireless Modes – Part 2
In the Shack
Spark transmitters used high voltage arcs which were
not only dangerous, but made one heckuva racket. The noise,
fire hazard, and smells of ozone and various burning things
(sounds like fun, doesn’t it?) caused the transmitter to be
frequently banished to a backyard garage or shed for safety
This resulted in the term “radio shack” which is still the
slang today for a ham’s station — no matter how neat and tidy.
Yes, that’s where the store’s name came from!