KB6NU's Ham Radio Blog

KB6NU's Ham Radio Blog

Antennas

Yet More Links

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Here are some more links I’ve found useful in my travels through the Internet:

  • Technick.Net. This site contains a wealth of basic electronics information, including pinouts for a wide variety of connectors and interfaces, tutorials on various electronics topics, and a section of circuits. The circuits section is a little light on ham radio circuits, but there are a lot of filter circuits, which could, of course, be useful in ham radio projects.
  • Station Grounding. This eHam.Net article is written by Steve Katz WB2WIK, and if you read eHam at all, you’ll recognize the call. He’s one of the more sane regulars there, and he has certainly earned his technical chops.
  • Clifton Laboratories. This website is the brainchild of Jack Smith, K8ZOA, author of Programming the PIC Microcontroller with MBasic. It has information on his amateur radio projects, including several PIC Microcontroller projects. There’s also some good information on how to work with surface mount devices.
  • Hobby Projects. Hobbyprojects.com is a collection of links to 1000’s of Electronic Circuits, schematics, online tutorials. There is a lot of good information here. Unfortunately, the website design really bad (think “angry fruit salad”), and there are Google ads all over the place.
  • Residential Electrical Circuits Explained. This page explains in very basic terms how electrical circuits work. It links to a bunch of other pages that explain voltage, resistance, current, and other electrical topics.
  • Business Studies: Broadcasting and Its History. One of my readers submitted this link, which is a succinct history of radio and TV broadcasting in the U.S.

Lotsa QRP Links

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Ron WB3AAL has updated the QRP Links page on the Eastern PA QRP Club website. There are links to:

Ron’s looking for more QRP-related sites to add to the page. If you know of any, e-mail him.

Shining a Light on the SG-239 Antenna Tuner

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This spring, I volunteered to help Colin KD8CCQ get on the air. He had an Icom IC-706 and an SG-239 antenna tuner, and was trying to figure out the best type of antenna to use with this combination. My solution was a doublet fed with ladder line, so one cool spring day, we strung one up and connected it to the SG-239.

Unfortunately, we did not get the results we were looking for. The tuner never did find a sweet spot, and we ran out of time that day to play with it more, and before we got back to it, Colin had decided to purchase an Alpha-Delta multiband dipole. We put that up, and it did work, so fortunately, Colin was able to get on the air.

After this experience, Colin thought that the SG-239 was defective, and was ready to send it back, but I wasn’t so sure about that. I convinced him to let me take it home with me so that I could play around with it. I wanted to hook up my dummy load to the antenna input. If it could tune a dummy load, that would, at least indicate that it was somewhat working.

Well, it sat on my shelf for a couple of months, but this weekend I pulled it down to run some tests. The first thing I did was to read the manual. (I know this is against FCC rules, but I had to chance it.)

It outlined a test procedure for the tuner that harkened back to the early days of ham radio–it suggested using a light bulb as a dummy load! Back in the days of tube gear, it was very common to use a light bulb as a dummy load. True, most light bulbs are not 50 ohms, and their resistance undoubtedly changes as the wire inside heats up, but most tube gear had matching circuits on their outputs that you tuned when you fired up the rig on a particular frequency, and they were beefy enough to tolerate more than a wimpy 1.5:1 SWR.

Besides, in this application, it’s probably a good thing that the load presented by the light bulb isn’t 50 ohms. Not being 50 ohms, will make the tuner actually do a little work. The 60W bulb I had measured 17.5 ohms, which should yield a 3:1 SWR.

Anyway, I first had to make some cables: a power cable for the tuner, a cable to connect the output on the antenna tuner to the light bulb, and a coaxial cable to connect the rig to the tuner.

After hooking it all up, I fired up the radio. The tuner clicked and whirred, and in a couple of seconds, had found a match. The tuner’s TUNED light came on, and the bulb glowed brightly. So, apparently the tuner works just fine on the bench with a dummy load attached.

Next, I plan to try it with either a homebrew end-fed Zepp similar to the one on eBay or a W3EDP antenna. Maybe I’ll finally be able to get on 80m.

For more information on the SG-239 antenna tuner, read N9ZRT’s All About The SG-239 Antenna Coupler: A Simple, Imperfect Tutorial

From the Mouths of Babes…

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Yesterday, ARROW members met for the monthly AMPTeam meeting. I had intended to play around with the crossband repeat function of my IC-207 VHF/UHF transceiver, figuring that crossband repeating could be useful in an emergency. After some manual searching, however, I determined that it doesn’t have that capability! I don’t know how I got the impression that it did. Oh, well.

Instead, I set up the KX-1 as usual. For an antenna, I use the antenna described in the antenna tuner manual, namely a 28-ft driven element and a 16-ft. counterpoise. I actually use three counterpoises–that seems to work much better than just a single one.

In my toolbox, I have a tennis ball and a ball of nylon twine. I poke the twine through the tennis ball, and then throw the ball over a convenient tree branch. The last time I set up out in a park, I snagged the perfect branch on the very first throw. Last night, however, I wasn’t so lucky.

The problem seemed to be that there was just too much friction between the tree bark and the twine. I’d get the ball over the branch easily enough, but the ball was too light to come down far enough to grab it and attach the antenna wire.

All this was quite amusing to the kids who’d come over to watch me. At first they asked what I was doing, and when I explained, they seemed really interested. After a couple of tries, I said to them, “The ball is going over the right tree branch, but it’s not heavy enough to come down the other side.”

I poked around in my toolbox, trying to find something that might make the ball a little heavier, but nothing seemed very easy to use. When I mentioned this to the kids, one of them piped up, “Why don’t you put some rocks in it?” What a perfect solution! They scouted around for some small rocks, which we poked through the hole in the tennis ball, and voila, it was heavy enough now to not only go over the branch, but pull the twine down the other side. I thanked my assistants, who seemed very pleased with themselves.

After untangling the coil of antenna wire and pulling it up into the tree, I got the KX-1 all hooked up and let them listen to some Morse Code. Unfortunately, I forgot to bring along my battery-powered speaker, so we couldn’t all listen to it at the same time. Next time, I’ll remember, though.

I made three quick contacts. The first with K1NUN, yet another card to my collection of QSLs from stations whose callsigns spell words. Next, was KE4RUN, another guy whose call spells a word, but I already have his QSL. Then finally Bob KB3ENU. Although Bob was also QRP, he was peaking at S7 here in Michigan, and we had a fine QSO.

Overall, it was another fine outing for the AMPTeam.

Knots and Ham Radio

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I did not have an illustrious Boy Scout career. I think I lasted three weeks, a month tops. The reason? I couldn’t quite fathom why I should learn all those knots that seemed to be the basis of Boy Scouting.

Now I know. Knots are extremely useful, even if you’re not going to be going camping a lot. In fact, they’re extremely useful in ham radio, especially on Field Day.

With that in mind, the ARRL published the article, “The Knots of Ham Radio” in the June 2006 QST. The most useful knots covered in this article are the sheet bend, the bowline, and the clove hitch.

The sheet bend is a good knot to use to connect two ropes of different diameters (the square knot is prone to coming apart). The bowline is a good knot to attach a rope to the end insulator of an antenna, and the clove hitch is useful for tying the other end of that rope to a tree branch.

One knot that the author did not cover, but that I learned from Bruce KD8APB is the taut line hitch. This knot allows you to quickly and easily adjust the tension on a line, which is a good thing when you’re playing around with antennas. You can find out how to tie that knot at the I Will Knot website.

It does take a little practice to master these knots, but not overly long, especially once you recognize the utility of them. I’m sure that learning them will make my ham radio life easier.

The W3EDP Antenna

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I have never operated 80m from my home. I have never had the space for a full half-wave dipole, and haven’t really had the motivation to put up anything else. Well, I’ve stumbled across something that may work—the W3EDP antenna.

The W3EDP is an 85-ft. end-fed wire with a 17-ft. counterpoise. Of course, you need an antenna tuner to make this work, but I already have a tuner or two here. And, if you’re going to operate QRP, a small tuner is even pretty easy to build.

Here are some links:

While Googling for information on the W3EDP, I also found a great article on building a current-type 4:1 balun on the N0SS website. The article was written by W1CG.

UPDATE 11/19/06: This afternoon, I strung an 85-ft. wire up into the trees, connected it to the T-1 longwire antenna tuner, and then put the antenna tuner on it. Several messages in the links above didn’t seem to think that the counterpoise was necessary for 80m, so I left it off.

The first readings were a bit perplexing. The SWR was jumping all over the place, and no matter what position I set the controls, I couldn’t get the SWR much below 3:1. Thinking that the 17-ft. counterpoise might be needed after all, I connected and fiddled with the tuner controls once again. This time, I was able to achieve an almost 1:1 SWR.

At this point, I decided to pack it all up and head back inside. It was gray and cold, had started to snow, I didn’t have an enclosure in which to stick the tuner, and the piece of coax that I had connected to the tuner wouldn’t reach to the shack anyway.

Overall, though, I was quite pleased with this experiment, and I think that it won’t be long before I’m on 80m.

More on the C-Pole

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I’ve written about the C-Pole antenna before. A friend, Mark W8FSA, and I bulit a couple of them for Field Day a couple of years ago. They’re vertical antennas, but don’t require any radials. On Field Day, we’ve found them to be good performers.

In the original article, which appeared in the April 2004 QST, the author gave dimensions for the 20m band and up. I thought this might make a good antenna for 40m, too, so I emailed the author, who graciously ran the numbers through his antenna modeling program and sent me the dimensions for a 40m C-Pole. Unfortnately, this was two years ago, and I have since changed computers and lost that email in the shuffle.

Well, Mark has come to the rescue. He found an online C-Pole dimension calculator. Thanks to the Sangamon Valley Radio Club for making this available!

I don’t know that I’ll get around to making this antenna before this year’s Field Day (it’s only a couple of days away), but I do plan to biuld one sooner or later.

Build an Antenna Mast from Irrigation Pipe

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For the past several years, my club, ARROW Communications Assn., has been fortunate to have the use of a big hay field at Domino’s Farms. (Yes, Domino’s Farms is home to Domino’s Pizza, one of the two biggest pizza chains in the country.)

One of the cool things about this site is that it’s close to the city of Ann Arbor, yet as the name would imply, out in the country. We set up in a big hay field that they mow for us just before Field Day. One of the features of this hay field is the irrigation pipe, which we put to use as antenna masts. We simply guy 30-ft. sections of this pipe to support all manner of wire antennas.

Having had some experience with the use of irrigation pipe as an antenna mast, I was happy to find the website, APRS Antenna Mast. This site explains how to build a 55-ft. portable mast from damaged sections of irrigation pipe. Very cool and very cheap.

Yet Another Antenna Idea

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Here’s an interesting idea for a portable 20m antenna from Ed K9EW via the Elecraft mailing list:

As long as you mentioned the inverted vee, I thought I’d offer this to think about. I have been using a 20m center-fed inverted vee with very good results. And here’s the great thing about it… it’s a coil of TV twinlead.

One end of the twinlead is split to form the two arms of the vee (each approximately 17 feet long), and then the remainder of the twinlead becomes the feedline which you can connect directly to your rig. The only constraint is that the feedline portion of the twinlead *must be* an electrical half-wavelength long (about 29 feet, depending on the velocity factor of the twinlead you use) in order to present a 72-ohm impedance to your rig.

It’s small (rolled up), lightweight, and requires one branch about 30 feet off the ground for the vertex. At this height, it’s approaching a half-wavelength above the ground which is great for the radiation pattern. The ends are tied off with small ropes to stakes (or rocks) 30 feet from where the feedline would touch the ground. This will give you a 90 degree angle at the vertex. It’s balanced, so no counterpoise. And it works just like a “home” antenna.

72/73, ed – k9ew

I just knew I’d find a use for that 300-ohm twinlead I bought at the dollar store a couple years ago. :)

Fiberglass Pole Sources

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On the Elecraft mailling list, there has been a lot of discussion about fiberglass poles for antenna supports. Here are some of the suggested products and sources:

  • The DK9SQ telescoping 33 ft mast is available from Kanga US. It’s $99, plus $7 shipping.
  • SpiderBeam sells a 40-ft. pool. Although SpiderBeam is a European company, Wireman sells them here in the U.S. for $99, plus shipping.
  • Possibly the best deal is the Jackite 31-ft. pole. From the product description on 5Stores.com, it looks as though they are meant to be used as supports for bird kites. The 31-ft. pole costs $42.95, a 28-ft. pole is $34.95.