Wednesday, December 23, 2009

Home-brew Antenna

When I picked up my FT-100, I had a problem… it requires an external antenna. I did the newbie thing at first, and shelled out some cash for an 8’ VHF antenna (it’s nice – I like it a lot). But they didn’t have an HF antenna available. For the first week or two, I was content just having VHF access. Had a great time, in fact, messing around trying out simplex (just couldn’t quite reach all the way to Santaquin – I think I had the power to go the distance, but there’s a big mountain in the way). But eventually I needed to try HF, and that meant I needed an antenna.

Ham radio is a lot like IT. You’re constantly faced with the decision of build vs. buy, of ‘make do’ vs upgrade. I’m pretty new when it comes to electronics and all things electrical, so I figured I ought to try to build just for the experience! I did a lot of research, and finally ended up with the $4 dipole antenna recipe. It’s a pretty simple dipole—the biggest challenges I faced were 1) the balun and 2) grounding it.

My alternative was a quick-and-dirty dipole from someplace like Ham City. They sell an MFJ all-band dipole for around $40 which would have been perfect for me. But you know, I had already chosen to build. ;) All-band would allow me to receive on 160, 80, 40, 20, 10 meters. My license only allows me to transmit on 10m, but I’ll be testing for my general license soon, so all-band is important. Remember my little FT-100 is an all-band radio.

Four Dollars Can Quickly Become $40

The author of the $4 antenna had it pretty easy. You see, he’s a long-term ham. He has a shed full of odds-n-ends. I do not. So my $4 antenna quickly jumped in price as I purchased

  • some twin-lead ($18 at Radio Shack, because they only sell it in 100’ lengths now),
  • PL-239 connectors, adapters, etc (another $15).
  • #18 lamp wire ($5)

Soon my antenna had jumped to $30, then right on through the $40 mark. And that doesn’t include the hours spent driving to Home Depot and Radio Shack. By the way, Radio Shack doesn’t sell much along the lines of radio stuff anymore!

But It’s About the Learning

But OK, it wasn’t just about saving money (although that was the ultimate goal). It’s also about the experience! Soon I was hunched over a pile of wire on the kitchen table, madly splicing, cutting, and prepping. I build my antenna from two 35’ legs of #18 insulated lamp wire (it’s a dipole, after all), which meet up and connect to a coax splitter in the middle. The lamp wire and splitter needed a good stable base to connect on—nothing better than an old DVD! I cut some holes, threaded the lamp wire through, and tied knots in each end of lamp wire to hold them in place. I then cut a couple of slots in the DVD, through which I threaded the twin lead. I spliced the antenna and the twin lead with electrical tape. Finally, at the end of my twin lead, I attached a very standard coax splitter – twin lead feeds in, coax feeds out.

AT this point, I have to admit I was pretty crest-fallen. I mean, this is the ugliest antenna at the ball! It’s hacked together with duct tape and spit. I was convinced it was worthless, but I had $40 into it already – no sense in giving up!

Oh, and problem #1 had been solved, sort of… I simply ignored the lack of a balun. I figured this is just my first antenna and it’s going to be ugly. It probably won’t work well, but if I can even listen to one QSO somewhere, it’ll be worth the effort. Right?

Nothing Else Is Grounded In There

Remember problem #2 – how to ground the antenna? Yeah, so did I… So then I came up with the answer: nothing in my attic (speaker wire, CAT-5, etc.) is grounded either. I figured throwing the antenna up in the attic couldn’t hurt, and any lightening strikes should be picked up by the trees, lightening rod, or my nice new UHF antenna. Right? So in I went – crawled around in the attic, stringing up this antenna.

Wouldn’t you know it? My attic’s roof joists have a support in the middle of them. The rectangle formed by all these joist supports just happens to be… exactly… 70’ in diameter. In other words, I just built myself a rectangular antenna. Which, in fact, is a pretty impressive and productive antenna design! Sometimes, things just work out.

So after stringing it up, I ran a coax cable out of the attic into my radio desk. With a quick adapter in place, I connected up to the FT-100 and fired her up. For the first time ever, I started browsing the lower bands. And guess what? I started hearing things! As low as 160m I could listen in on QSO’s. I have to tell you, I was pretty excited about that.

It Won’t Fire If You Don’t Push the Button

So for about two weeks, I listened in now and again on QSOs. Some were pretty impressive – I heard folks in Michigan and Minnesota in a conversation down on 160m, as well as a bunch of various other unidentified locations. I picked up a lot of CW, too. I was experimenting with a bunch of signal processing and other filtering as well. Still, up to this point, I hadn’t fired anything up at all.

Well, one evening I was sitting around looking at the band plans and decided to give it a go at 10m. I figured I’d smell smoke before I burned the place down, and there was only one way to see if my antenna was going to work or not. So I flipped to the calling frequency on 10m, powered the radio up to 100%, and keyed up the mike. I called out “KF7DVJ CQ CQ CQ” and waited. Not five seconds later, I heard a response! We had a good, brief chat—and I found out my QSO was with a gut just east of Sacramento. That’s more than 600 miles from here!

My little home-brew antenna is fun. I admit, I spent more than what it would have cost to buy a commercial dipole (and there’s one under the Christmas tree anyhow), but I had a good time. I’ve got an antenna I can take places with me, if I want. I am still amazed at the success I’ve had with my homebrew antenna and my FT-100’s autotuner. To have reached as far as Sacramento on 100 watts and a home-brew dipole stuffed in my attic?

I’ll hang my Christmas dipole shortly—it’ll be outdoors, at a recommended height. I’ll probably pull in a lot more stations, but nothing can replace what I learned and the thrill I had with that little home-brew. I’ll continue experimenting with home-brew stuff (next is a little 2m Yagi, then a field day go-kit for my FT-100, a couple of batteries, and a solar panel), too. That’s what ham radio is all about – chatting and learning!

73’s and happy holidays.