The Amateur Amateur: Dallying on the Digital Modes

By Gary Hoffman, KB0H
Contributing Editor
August 22, 2005

Hams with digital-mode experience likely would have been able to identify the particular signals by their distinctive sounds, but I just clicked on the mode buttons until something intelligible began appearing on the screen.

The MMSSTV screen. Note the vital Auto button.

Many pictures I received were unreadable or scrambled.

In my last two columns I explained how curiosity about PSK31 prompted me to figure out how to run digital modes on my HF transceiver. Initially there was a certain amount of puzzling and fumbling, but once things started to work, it was like opening the door to a whole new world! Digital modes are kind of addictive. Something about running the whole show from my computer appeals to me.

Once again I'd like to thank all those swell Amateur Radio operators who wrote all that really nifty computer software that is necessary to make digital modes work. Without their labor and generosity far fewer hams would be using these fun modes.

I started out with the intention of just trying PSK31, but I noted that options included in some of the PSK31 programs made it just as easy to try other digital modes. Well, it was just too tempting. I just had to sample some of them.

Not being all that familiar with who does what and where in the digital world, I just scanned through the digital subbands until I heard something that sounded like data. Hams with digital-mode experience likely would have been able to identify the particular emissions by their distinctive sounds, but I just clicked on the mode buttons until something intelligible began appearing on the screen. Most signals I encountered were PSK31, but I did stumble across a RTTY conversation or two. Some of the software would even handle Morse code, but I seldom tried that. Somehow using a computer to decode Morse felt a bit like cheating.

But others came out near perfect.

Quite by accident I discovered that there was a fledgling emergency digital net active in Missouri. It used MFSK16 format, which incorporates more error-correction features than PSK31. I had not tried MFSK16 before, and it took just a little bit of experimenting before I got it right. Soon I was able to check into the Missouri Emergency Digital Net. Participation was light, and the net seemed to fade away, but I suspect that it will be revived as more hams get involved in digital modes. I hope so. I rather enjoyed hearing the cheerful warble of MFSK16 data coming over my transceiver's speaker.

I quickly discovered that slow-scan television (SSTV) was just as easy to send and receive as all of the other HF band digital modes. As with PSK31, RTTY, and such, free software was available to send and receive SSTV. With no additional equipment, I should be able to transmit my own pictures over the air. Now that was just irresistible. I quickly downloaded and installed the freeware program called MMSSTV.

Written by Makoto Mori, JE3HHT, MMSSTV is a marvelous piece of computer code. It has all sorts of options which, on initial inspection, baffled the heck out of me. Just staring at the MMSSTV screen it became obvious to me that there was not just one format for sending SSTV pictures, there were several. They had evocative names such as Robot 36, AVT 90, Scottie 1, and Martin 2.

I still have no clue as to what all that means. Fortunately I didn't need to know, because the program had the one magic button all novices seek, the one marked "Auto."

The next trick was to find SSTV signals on the air. I scoured my collection of band plans and wrote down everything that mentioned SSTV. I checked all of the frequencies I'd assembled and ascertained that I was most likely to find SSTV aficionados on 20 meters around 14.230 MHz.

As with any new ham radio endeavor, I listened first--or, in this case, watched. Luckily for me MMSSTV didn't require a lot of user intervention. It managed to grab signals out of the air, decide which formats had been used and interpret them.

Receiving my first picture was quite an experience. The noise coming from my transceiver was reminiscent of special effects from a science fiction movie. But even more fascinating was the image being assembled line by line on my screen. It didn't look like much and it was full of static and lines that weren't contiguous, but it was still recognizable as a picture. I flopped back in my chair with my mouth hanging open and marveled at it. It was a wondrous moment. I suspect that every SSTV operator felt that way when his or her first image appeared.

I'm still dallying with the digital modes. I monitor the occasional PSK31 conversation. If I hear some data stream making unfamiliar music with tones I'll play around to see if I can decode it. But more and more often I find myself camped out on 20 meters hoping to pull in some static-ridden, but still beautiful image via SSTV.

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