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The Amateur Amateur: Slippery-Slope Television

09/28/2009

Our ARES group is going to put on a field station demonstration next month. This will be our third such event, and I'd operated a HF PSK31 station at the last two. I told Chuck -- who will be the site manager this year -- that I hadn't felt I'd accomplished very much during the previous demonstrations. True, I'd had few visitors and made even fewer contacts, but I asked if there was something else I could do, something with a bit more pizzazz, something that might actually draw attention to my station.

Chuck suggested slow scan television (SSTV). We'd had operators working SSTV at the previous events, but not steadily and not always successfully. Chuck felt that if I kept a SSTV station going all through the event and sent images to an unmanned receiving station at our welcome table, it would be a real eye-catcher.

That sounded pretty good to me. I figured that I could take a digital camera with me, take pictures during the event, and then transmit them. It would certainly be more interesting than watching a waterfall display of static all day.

"Lighter and Fluffier"

Chuck and I started working out what I would need. I could operate on 2 meters, which would mean that I wouldn't have to take a massive antenna. In fact, all I would need as a receiving station would be a laptop computer and a hand held police scanner. Cool! That would be one less huge battery to load into my car.

So that was the theory. I would need two laptop computers, one 2 meter transceiver and one police scanner. But as we all know, theory is one thing and reality is another. I decided to run a test. I didn't have two laptops (Chuck would supply the second one on the day of the event), but I did have a laptop and a desktop down in my basement shack.

I had run SSTV before, but with different radios and computers, and on HF rather than VHF. So I started slowly. I went through the tangled mess of cables and wires (I really must straighten that stuff out someday) and connected a transceiver to each computer. I know, I said that I would use a police scanner -- and I still planned to -- but first I wanted to send and receive with equipment I was already confident would work.

"Operation Popcorn"

And naturally, it didn't.

The field radio transmitted and the base station received, but the image I got was a mess. It looked like some bully had come along and kicked the top of it, causing it to topple over at a weird angle. It wasn't straight, it sloped.

Repeated attempts just resulted in repeated failures.

Okay, Plan B. I tried sending from the base station and receiving on the field radio. That resulted in no image at all. The base station transmitted a carrier wave but no data.

Now I was deep in the well of frustration. I had two major problems to solve and I hadn't even hooked up the police scanner yet.

Plan C. And to be truthful, it wasn't really planned. It was more like Desperate Act C. I disconnected everything and plugged the base station into the laptop and the field station into the desktop. This yielded much the same results: No image from one transceiver, and a sloped image from the other transceiver.

At this point I was pretty of confused. I wasn't sure what I'd accomplished. I decided to take one of the transceivers out of the equation and plug in the police scanner instead.

That finally produced something positive. I did, at least, prove that the police scanner could receive SSTV images. They were still sloped, mind you, but at least the scanner received them.

Time for Desperate Act D (or was I already on E?). I reached up on the shelf and pulled down the manual for the base station. If all else fails -- and I mean everything else -- read the instructions.

Intermission

Hmmm. As with many manuals, the instructions weren't 100 percent clear (which is probably why so many of us avoid reading them in the first place). But I did get the sense that the DATA port was meant to be used for HF operations and the PACKET port was meant to be used for VHF operations. I decided to test the theory.

Yep. Even though I wasn't running packet mode, the PACKET port was the right place to send and receive data while I was using the 2 meter band (actually, I now believe that it may not be the band that matters, but rather whether the transceiver is in AM or FM mode). My base station finally started sending SSTV images.

The results were dramatic. The images now sloped the other way.

I leaned back in my chair and let out a sigh. It wasn't exactly what I'd wanted, but at least I'd made some progress. I could now send sloped images from both transceivers.

Up to this point I'd primarily focused on the transceivers. I switched my attention to the computers. For a while I thought that perhaps the sound levels had something to do with my problems (I was sending and receiving through sound cards rather than TNCs). But that didn't seem likely, as the symptoms on both systems were almost identical. I also spent time checking the program settings, but they were so voluminous and cryptic that I couldn't tell what they meant. And so, for the second time that evening, I decided to read the instructions.

I need to mention here that I was using the MMSSTV freeware program, written by Makoto Mori, JE3HHT. Any failures were entirely due to my own ineptitude and not Makoto's marvelous software.

And upon reading the instructions (yes, Makoto even included a HELP file), I saw right there in the table of contents something called "Slant Corrections." Oh, how I wished that I had read that first!

(I told this story to my wife shortly after the events took place. When I reached the part about finally reading the instructions, she doubled over, clasped her mid-section and said, "Don't make me laugh, I already have a stomach ache!")

"It's Getting Kinda Weird Around Here"

Ahem. Where was I? Oh yes, slant corrections.

The HELP file explained why the slants (sloping images) occurred (slightly different recording and playing frequencies in the soundcards). The program had a way to compensate for the differences and gave simple, explicit directions. I followed them and...

Yes! The slopes disappeared! (for the most part). The images that I sent and received were now quite viewable.

I performed the procedure on both computers. The desktop only needed a slight adjustment, but the laptop was way off. It was no wonder that the images looked so screwy.

Anyway, I had proved what I had set out to prove and I had learned something in the process. It may have taken several hours more than it should have, but at least I did learn it.

And as we all know, the most important part of learning something is using it to make yourself look brilliant. I immediately wrote a message to Chuck, explaining in a very scholarly manner that there was a procedure that he needed to perform on the laptop he was going to provide...

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.

 

Gary Hoffman, KB0H
Contributing Editor



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