The Amateur Amateur: Pouncing on Digital Modes

By Gary Hoffman, KB0H
Contributing Editor
July 17, 2005

I was ready to transmit on PSK31 but didn't want anyone to hear me if I messed up.

Last time, I recounted how I started investigating digital modes, got an interface to connect my computer with my transceiver and obtained free software to make it all work. Now let me tell you what I saw and heard.

There are a number of digital mode freeware and shareware programs available. I chose HamScope just because I thought it looked pretty (DigiPan is another popular--and free--PSK31 software package). I've found that HamScope has many more options than I'll ever need, but when I'm bored I try some of them just to see what happens. So far I haven't damaged anything.

PSK31 waterfall

The HamScope software "waterfall" display, showing multiple conversations (the vertical bars) on one radio frequency.

Anyway, I spent a lot of time just fiddling around and gazing at the waterfall--the visual display of what I heard on the speaker. One nice thing about typical digital mode software is being able to hear and "see" the signal at the same time.

"Ah, so that's what that electric line noise looks like!" I'd say to myself.

I'd never been adept enough to work the ancient oscilloscope that someone had given to me, so this sort of thing was all new territory.

Eventually I got around to looking for actual digital-mode signals. I was most interested in picking up PSK31 transmissions. FYI: PSK stands for Phase Shift Keying, which is the modulation method used to generate the signal. The 31 is the bit rate, which, not to be too fussy, is actually 31.25 Hz. PSK31 signals are not hard to find. Just as with voice modes, if the bands are open, someone will be transmitting a digital signal.

For those who've never had the experience, let me take a moment to describe operating in PSK31 mode. PSK31 is a keyboard-to-keyboard mode. In really simple terms, you type a message, and it appears on the receiving station's computer screen. When the other op responds, his or her message appears on your computer screen. From a completely non-technical standpoint it's a little like being in an Internet chat room.

What you hear on your transceiver is a sort of chirpy-warbly sound. Its pitch depends on what part of the audio spectrum the sender uses. Since a PSK31 signal occupies very little bandwidth you can pack a lot of signals onto one radio frequency. On a good day you can, in fact, tune to the favorite PSK31 hangout on 20 meters, 14.070 MHz (±2 kHz), and "see" several conversations going on at the same time. Regrettably you can't monitor them all at once, although HamScope and some other popular software packages will let you copy two messages at the same time.

Rascal and 'extra' cable

Oops! The extra cable does do something after all.

The day finally came when I felt confident enough to try sending my own message. Rather than trying to jump into an existing conversation I started transmitting on an unused part of the audio spectrum. For that matter, it was an unused part of the radio spectrum, since there were no conversations taking place. In fact, the whole band was dead. I was ready to transmit, all right, but I didn't want anyone to hear me if I messed up.

Well, it was kind of cool. The waterfall display changed dramatically, showing only my transmission. And I quickly figured out that I had to stop transmitting manually or my rig would keep on pumping out my lack of keystrokes--an idling signal. Within a few minutes, however, I found the proper way to end my transmissions automatically.

One thing puzzled me, though. Although the waterfall display showed my transmissions blasting away into the ether, I didn't notice any change in what I was hearing from my transceiver's speaker. Okay, you've figured it out already, but I've given you all the clues. At the time I was focused on what I was seeing rather than what I was hearing. While I hate to admit it, it took me a few minutes to figure out that I wasn't actually transmitting anything. The computer said I was, but the transceiver sat there placidly, not sending a thing. And again, this is embarrassing, but remember that extra plug that I mentioned in Part One of this story? It suddenly became clear what it was supposed to do.

LU5DIT QSL card

A card from Argentina confirming my first DX on PSK31.

Okay, let me back up for a just a second. On my left side is the computer. On my right side is the transceiver. The transceiver has one cable plugged into its DATA port. This connects to a conversion box that splits into three other wires that connect to the PC. One cable goes into the speaker port and another to the microphone port on my sound card. And that's where my brain stopped working:

Hey, I had wires to receive data and to send data, what more did I need? Oh, yeah. What about that third cable? Well, as it turns out, that one lets the PC tell the transceiver when to transmit and when to receive. In other words, it acts like the push-to-talk button.

Even though no one saw me, my face was still red as I plugged that "extra" cable, which connects to the PC's serial (COM) port.

I soon got over my little faux pas and started transmitting for real. And quickly enough I was joining in conversations. My first PSK31 contact was with Wen Johnson, K7RME, in Tucson, Arizona. A week later I failed in my attempt to check in to a multistate earthquake drill, but I did succeed in making contact with the group running the drill via PSK31. And the week after that I made my first DX PSK31 contact with Juan Bilbao, LU5DIT, in Argentina.

Oh yeah! I can tell that digital modes are going to be a lot of fun!

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 Web page. Readers are invited to contact the author via e-mail, [email protected].

© 2005 American Radio Relay League


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