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The Amateur Amateur: Cablegrim

06/21/2011

By Gary Hoffman, KB0H
Contributing Editor

The cables are out to get me, there’s no doubt about it. I should have known as soon as my first DB9 serial to USB cable went sour on me. I attributed the problem to a nearby lightning strike, which did indeed scramble a number of my electronic devices. But a serial to USB cable? I should have suspected right then.

If that episode didn’t clue me in, the next one should have. It was a data cable from my wife’s notebook computer to an external disk (hey, you gotta have backup, you know). Sometimes the disk was available, sometimes it wasn’t. Oh, I spent a looooong time trying to figure out what was wrong with that disk. Or the computer. Or the software. Who would suspect an innocent data cable? I did, eventually, after eliminating everything else. I swapped in an identical cable and the disk started working just fine.

Having ignored the signs and portents up to that point, something came along and proved to me beyond a shadow of a doubt that the cables were definitely conspiring against me.

Walk This Way

It was supposed to be a simple project. No, actually it was supposed to be a simple task. It was so simple that it didn’t rate the status of being considered a full-fledged project. Just open a box, pull something out, close the box, and bada-bing bada-boom, it’s all done.

That was the theory, anyway. And then that simple task turned into... well, not exactly a major project. More like a curse.

I do a fair amount of communicating via VHF packet. For many of us, getting computers and transceivers to work together is something of a challenge. It’s like a bad marriage. There are constant arguments between the two “partners.” I measure my progress in the field of digital communications by how many broken components are lying around my shack, how many pages I’ve scribbled into my notebook and how much hair I’ve lost. I’ll just say that there has been a lot of each of those.

But what I wanted to do was so simple...

I have an Alinco mono-band transceiver that came with a built-in TNC (Terminal Node Controller). I used it for a while and didn’t like the way that the built-in TNC worked. I replaced it with a third party internal TNC, which worked even worse. Eventually, I just connected the Alinco to an external TNC (a Kantronics KPC3+) and got very gratifying results. The only thing that bothered me was that I had to connect the KPC3+ to the Alinco through the transceiver’s microphone and speaker ports. Oh, it worked fine, no question about it, but it prevented me from operating the Alinco in voice mode.

So here was the simple task: Open up the Alinco, remove the internal TNC card and then jump the DB9 data port on the back of the unit across the missing card and right into the transceiver’s electronics. That way I would be able to plug my external TNC right into the data port, and hence free up the microphone and speaker ports. The Alinco was even designed so that it could operate this way. What could go wrong?

Well, pretty much everything.

Do You Have a License for That?

It started, of course, with the data cable from the KPC3+ to the Alinco. I had several of them, simple DB9 to DB9 (9-pin connector) cables of varying lengths. I had even used some of them to connect my computer to the data port on the Alinco when its internal TNC was still in place.

But I had never tried to connect a KPC3+ to the data port on the Alinco. Both devices had female DB9 connectors on them, and all of my cables had male connectors on one end and female connectors on the other end.

Okay, you’re sneering and saying to yourself that I’m whining about a trivial problem. And you’re right. But that was just the start. I bought an appropriate male-male cable and it still didn’t work.

Now I had to fall back to that old standby: Read the manual. And according to the manuals, the Alinco and KPC3+ used completely different DB9 pins to communicate. More than that, the Alinco used one set of pins for 1200 baud and a different set for 9600 baud.

I had to make yet another purchase, this time for a pin adaptor kit.

You can see how this simple five-minute task was beginning to take on a life of its own.

I received the pin adaptor kit, performed a shaky-handed soldering job and managed to construct an adaptor to put it in-line between the Alinco and the KPC3+. Now, do you suppose everything worked at this point? Of course not.

Back to the manuals. And this time it took a lot of reading. I eventually found the answer to why my TNC and transceiver weren’t communicating, but not from what was in the manual, but rather what was not in the manual.

The Alinco has a “data mode.” Press a button and a little square wave icon appears on its screen. The manual says to set this when you use the internal TNC. It also says to set this when using an external TNC running at 9600 baud. But it does not specifically say to set the data mode when using an external TNC and running at 1200 baud. To me, it was sort of implied, since the data mode is set for every other digital operation. But apparently I was wrong.

I turned off the data mode and suddenly everything worked. Finally!

Oh, but the story isn’t over yet.

I Wish to Register a Complaint

You see, I have two computers, a desktop and a laptop. I also have two identical Alincos, and two identical KPC3+ TNCs. One set is for my base station, which remains in my shack, and the other is for ARES® field operations. In fact, there was only one component lacking before I could use both digital stations simultaneously.

Right. A data cable. This time I needed a DB25 to DB9 cable to go from the KPC3+ to my laptop computer. I already had one, which was attached to my base station computer. It worked fine. I bought a second cable from the same manufacturer.

It didn’t work.

Okay, maybe it was my fault this time. I bought a nine foot cable instead of a six foot cable. Maybe that was just too far to get signals back and forth between the TNC and the computer. A subsequently purchased six-foot cable worked fine. But I will tell you one thing…

Those cables really hate me.

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.



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