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The Amateur Amateur: One Medium Counterpoise, Hold the Anchovies

01/19/2009

Now to be truthful, I haven't tried very hard. Most of my Amateur Radio activity revolves around local efforts for an ARES® team. I've made the occasional stab at getting my HF antenna system to function properly, but when it doesn't work, I just give up and move on to some other project.

I did have a working HF antenna system at one point. It consisted of a simple wire stretched between masts at either end of my house, hovering just a few feet above the roofline. It was connected to a SG-230 antenna coupler, which did a reasonably good job of tuning it. I also had a random length of counterpoise that ran down the eave of the roof, down to the back yard and connected to a rod pounded eight feet into the ground. I later added a second length of counterpoise that ran down toward the front yard where it meandered aimlessly through ivy, bushes and other vegetation. There wasn't much planning involved -- I just ran wires where there was room to put them.

Amazingly, this system did work. It had great NVIS propagation (Near Vertical Incident Skywave), which was wonderful for local emergency communications work. Beyond NVIS, I also manage to work stations in Spain, Argentina, and Cuba. The antenna seemed just about perfect.

Trouble with Masts

So, what was the problem?

The problem was that every time I transmitted I generated RFI in the house. The electronic devices in one room of the house would go haywire. The computer speakers would howl, the printer would have fits and the three-way touch lamp would jump from one setting to another. After my wife Nancy informed me that it was very difficult to sit down and read a book in a room that seemed to be possessed by demons, I ceased my HF activities altogether.

That was back in 2005.

I thought perhaps that the RFI problems might go away if I moved my HF wire antenna higher up the mast. I didn't get around to testing this theory, though, until I installed a new mast. Once the new mast was in place, I mounted the SG-230 box much higher above the roofline.

That didn't solve the RFI problem, so I stayed off the HF bands.

I Want Candy

Now let's move forward to fall of 2007, just after Halloween. Nancy was raking leaves in the front yard. I was on the roof messing with the SGC antenna coupler and my wire antenna. I had decided to return it to its former location, since it had worked reasonably well there. As for the RFI, well, I figured it was unavoidable. The touch lamp had been replaced by a lamp with a manual switch, and I'd been told that computer speaker wires were notorious for picking up stray signals. Maybe I could dampen the effects with some RF filters. Even if I couldn't fix the RFI problems, I wanted to have an antenna that worked if I was absolutely desperate to get on the HF bands.

I had remounted the antenna coupler a few weeks earlier, but had left the antenna and counterpoise wires dangling from it in coils on the roof. I finished stringing the wires and climbed down from the roof.

"There's a lot of candy in the yard," said Nancy.

I went down to my basement shack and turned on my HF transceiver. I pressed the transmit key and said, "KB…"

That's as far as I got before the transmitter shut off.

This isn't good, I mused. What happened?

I keyed up again and watched the SWR meter.

Whoa! Not good at all. What had gone wrong? The antenna was back in its original position. What had changed?

Well, I had modified the counterpoise when I'd moved the antenna to a higher position months before. That must be it.

Back upstairs.

The young boy from next door was helping Nancy rake the yard.

"It's his candy," said Nancy.

"My cousin and I got into a fight on your lawn last night," said the boy. "Our bags broke."

I climbed back onto the roof and moved the counterpoise. I climbed down again and said, "Don't eat any of that candy on the ground. We'll give you some fresh stuff."

"Oh, I don't need it. I've got several more bags at home," the boy told me.

Down in the basement I found that the SWR reading had not improved.

Back up to the roof. Another repositioning of the counterpoise. Another check of the SWR meter. No change.

This went on for quite a while. Normally I would have given up by now, but this time I was determined to figure out what was wrong. And while Nancy and her helper filled bags with leaves, I moved the counterpoise wire to every imaginable position. I ran it down the rain gutter. I wrapped it all over the roof. I draped it along the ground in the back yard. Nothing helped, absolutely nothing.

I sat down in my shack and sighed. Okay, random actions hadn't accomplished anything. Maybe I should try to think my way through the problem. What's causing this horrible SWR reading?

It seemed to be the counterpoise.

Alright, what is a counterpoise?

Nominally, it's the one half of a dipole antenna.

Ding. A tiny little bell went off in my head.

Pizza Angel

Okay, I'm no expert on antennas. In fact, every time I think I've learned something about antennas, someone tells me, "Oh no. You've got it all wrong." But doesn't a dipole antenna consist of two segments of equal length?

Oh, I know. There are a million exceptions. But it was the only idea I had.

I climbed onto the roof, reeled in the counterpoise, and ran it in the same direction as the main antenna wire. I cut the counterpoise so that it was exactly the same length as the main wire, then just threw it so it lay randomly on the roof.

I went downstairs, checked the SWR meter, and got a beautiful reading. I keyed up and this time the transmitter didn't shut off.

"KB0H testing," I said.

"Read you fine in Kansas City, KB0H," replied a voice.

Success!

I went back up to the roof to work out a more orderly arrangement for the counterpoise. While I was cleaning up I noticed something sitting on top of the antenna coupler. I went over to see what it was.

It was a half-eaten slice of pizza. Apparently a bird had scavenged it from someone's trash and had put it up on the antenna coupler for safe keeping.

What a day. Candy all over the yard and pizza on the roof. At least the HF antenna was working again.

I know in my heart that cutting the counterpoise solved my SWR problem. But I can't help but wonder if at least a small part of the trouble was that I kept reheating that slice of pizza.

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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