The Amateur Amateur: Creeping up on the Digital Modes
By Gary Hoffman, KB0H
Getting up and
running on digital modes flitted into and out of my consciousness for
a few years, but then I discovered PSK31. Even watching noise was
June 8, 2005
I became aware of
Amateur Radio digital modes as soon as I began studying for my first
Amateur Radio license. RTTY is mentioned in the same breath as AM,
FM, and SSB in just about every book and pamphlet that describes our
hobby. I never gave digital modes much thought, however, until my
wife Nancy and I came across a ham radio demonstration held on the
grounds of the St.
Louis Science Museum
. A local club had set up a couple
of radios, and one of them was running packet.
Longwave, a personal computer just for my shack.
I asked the ham
at the packet station a few questions, and his answers interested me.
But being a newly-minted no-code Technician, I wasn't quite prepared
to jump into such a strange and exotic mode.
flitted into and out of my consciousness for a few more years, mostly
in the form of packet radio. Once in a while I would consider giving
it a try, but I backed away very quickly every time I picked up a ham
catalog and checked out TNCs--Terminal Node Controllers. The prices
caused my baud rate to skyrocket.
I decided to put
exploration of digital modes on the back burner for the time
being--the very, very
One pivotal event
brought digital modes back into focus for me. I decided to do a
column about Field Day 2003, and visited the St Charles Amateur Radio
Club's site (see Saturday
in the Park with Ray, Part I
in the Park with Ray, Part II
). The station
running PSK31 garnered more spectators than anything else at the
event. Not only was this an unusual setup for many of the onlookers,
but its operator was an 11-year-old girl!
That image stuck
in my mind and eventually prompted me to do a little research on
The first thing I
discovered was that radio amateurs have been experimenting with quite
a few digital modes over the years. RTTY, AMTOR and PACTOR were all
terms I'd come across while studying for my ham ticket, but PSK31 and
something called MFSK16 seemed to be the hot new modes
All of these
modes seemed to work by sending tones over the air, each letter and
number represented by some unique combination of those tones.
The magic sound card/transceiver interface. But what was the
extra connector supposed to do?
The second thing
I discovered was that those particular digital modes seemed to be
used primarily on the HF bands. Packet, while sometimes found on HF,
tended to be more common on VHF and UHF.
Ah, but my third
discovery really got me excited: One could run PSK31 using just the
sound card of a personal computer. I could operate in that mode
without buying an expensive TNC! Better still, I wouldn't have to
build a sound card/transceiver interface, since those babies were
already commercially available. Hey, I may like to experiment, but
I'm still fundamentally lazy.
A quick check of
my HF transceiver showed that it did indeed have a data port. More
joy: a sound card/transceiver interface was available for my specific
radio. I quickly ordered one. It arrived in short order, and I soon
had my computer and HF rig linked together.
There seemed to be one wire and a connector left over, but I didn't
worry about it. My main concern now was how to set up my computer.
A waterfall display. The vertical trace represents a signal.
Let me take
a moment to express my extreme gratitude to all the folks who have
developed today's digital mode software and
made it available
as freeware or shareware. I just can't say enough about these fine
people. Maybe I would have one day gotten around to building my own
adaptor, but I would never
have taken on the task of trying to
write a computer program. So, thanks guys!
There are a
number of freeware and shareware programs for digital modes. Some of
them are for one specific mode, such as PSK31, while others can run
several modes. A couple of them are so user friendly and flexible
that it's hard to believe they are free.
Some of these
programs contain an eye-catching feature called the waterfall
This is a continually changing display which shows the activity on
the frequency to which your transceiver is tuned. Now, at first this
display had me confused. I finally figured out, however, that what it
was showing me was the audio
spectrum--the same thing I was
hearing on my radio's speaker.
The waterfall was
fun to watch, even when I wasn't tuned to digital mode frequencies.
Actually, it was more than fun. It was instructive. Even watching
noise was interesting. It became clear that voices took up a lot of
space on the waterfall when compared to some sort of digital signal,
which took up relatively little space--or bandwidth to use a more
I already knew
that the typical human voice in radiocommunication systems like ham
radio spans roughly 300 to 3000 Hz--or a bandwidth of approximately
2700 Hz. Individual tones obviously have a much narrower bandwidth.
But it was cool to see this phenomenon displayed visually.
Next month I'll
tell you what I saw and heard, and--better yet--what happened when I
tried to send my own digital message. Stay tuned! And keep your eye
on that waterfall display.
Editor's note: ARRL member Gary Hoffman, KB0H, lives in Florissant,
Missouri. He's been a ham since 1995. Hoffman says his column's name
-- "The Amateur Amateur" -- suggests the explorations of a
rank amateur, not those of an experienced or knowledgeable ham. His
wife, Nancy, is N0NJ. Hoffman has a ham-related
Readers are invited to contact the author via e-mail,
© 2005 American Radio Relay League