The Fugue

I had one of these antennas:

Not top of the line, I know, but it did have an amplifier and it did cost probably $30 when I bought it. And it’s pretty much worthless. We got the PBS station in town but rarely could we pick up any of the El Paso stations.

Now that we’re on the DTV bandwagon, I set out to improve the antenna situation. Antennaweb told me that I should be able to pick up almost all of the stations with a “yellow” antenna—a small multidirectional antenna (actually one station called for a medium directional w/pre-amp, and antennaweb doesn’t realize some of those stations are broadcasting digital on UHF channels for now). In other words, it should be easy to get those stations. So I did a little searching and researching. All the digital stations here are UHF, so all I really needed was a UHF antenna.

I decided to make me a simple loop antenna—the same design as the UHF component on the one I already had. I fired up a wavelength calculator and figured out that the center of bandwidth for the channels I was interested in (15,16,17,18,23, I found that with the help of HDHomeRun’s Channel Page, although my strongest station was mysteriously absent there) was almost exactly 2 feet (Here is an excellent TV Frequencies Table. Remember λ=c/f=3e4/MHz.). So I cut a coat hanger at 2 feet, shaped it into a circle, and soldered on a female coax connector. There are pictures here.

I found that it didn’t work much better than the other one in the same position, but as I moved it around and found a good position I got a satisfactory signal. So, to be rigorous, I tried the other antenna in that position. It was pitiful. So I was still justified.

I ended up hanging it on a nail on the wall, where it gets satisfactory to excellent reception for every station. Total cost: under $5.

If you need a directional antenna in your area, you might still be able to do this, and add a reflector (cardboard with aluminum foil) ¼ wavelength on the far side. I held a piece of foil behind it and it improved the signal strength quite a bit. Just how to rig that up is your problem, but I suppose some pieces of 2×6 and some nails and washers (and electrical tape for insulation) would do the job.

Speaking of electrical tape, if you look at those photos you’ll see that there is a bunch of electrical tape scraps on my loop. That’s just because I reused the hanger from my coat hanger dipole when constructing it. Which is an excellent VHF antenna, if your stations are VHF.

In a previous post I talked about my new scanner and my early antenna adventures. Now I am happily set up and done playing with antennas, so I thought I’d tell you what the final verdict is. Also, it has been requested that I post some pictures. The pictures are here, and I’ll embed some of them in this post.

The antenna I’m using is actually not the one I described making in the previous post. It would have worked fine, but I found the functional equivalent at Radio Shack for $5, only slightly more robust. Here’s a picture:

It is sold as an FM antenna. I think the package said dipole, but it’s actually a folded dipole. I clipped the ends to match my target frequency, then soldered the leads together and put some electrical tape on for protection. Even when it was just an FM antenna it got better reception than the rubber duckie.

It is attached to the radio via a TV balun (300Ω to 75Ω) and a female TV-style coax to male BNC adapter:

I also constructed a dipole using coat hangers and electrical tape. I need to get a connector for this, since the balun is unnecessary, but even when I hook it up to the balun it does very well. I think the coat hanger being thicker helps. I think it even outperforms the folded dipole, both my custom one (not shown) and the FM antenna. A bit unwieldy though, compared to the FM antenna.

Speaking of baluns, I asked an expert and his unofficial opinion is that for reception only impedance mismatch isn’t a big deal. Certainly seems to be the case in my limited experience (even with the TV balun, it’s 75Ω when the scanner nominally wants 50Ω). Still, the TV balun makes a nice adapter, and it can’t hurt. They’re very cheap, too.

I got a handheld radio scanner for my birthday and Christmas with the cash I received (thanks, everyone!). I got a RadioShack PRO-84 on sale for $60. It can scan lots of different things, but I’m primarily interested in listening to aviation communications, which is from 108 MHz to 137 MHz. I’ve found the scanner to be quite satisfactory, with the minor annoyance that it is difficult to listen to an arbitrary frequency without assigning it to one of the 200 numbered channels (so I pick a channel or two as my temporary channels).

Although it works great for listening to traffic at the airport, for listening to traffic away from the airport (e.g. at home), the included “rubber duckie” antenna is not up to the task. So I set about making my own.

I went from knowing nothing about antennas to knowing just enough to sound like I know what I’m talking about, and apparently to build a simple one. I learned a few interesting things in the process.

One simple and decent antenna is the dipole. You may be familiar with a version of the dipole known as rabbit ears. What you may not realize is that the rabbit ears work best completely horizontal (not in a V shape) and adjusted in length to match the frequency of the desired television station. Also, they need to be pointed in the right direction (broadside the transmitter) for best reception, and they should be away from the TV. So much for TV antennas.

So I had decided on making a dipole, and started seeing claims that this variation called the folded dipole is “quieter” and has “more bandwidth”. It is almost as simple to make as a dipole, so I decided to go with that. Now it was time to figure out how to make it cheaply. I’m happy to report I was able to make the antenna for $5 and change, and it works quite well. I am sitting in Pleasant Grove, scanner and antenna indoors, listening to Provo traffic, including planes on the ground. I imagine I’ll have similar results at home where the terrain profile is similar between my house and the airport.

So here’s what I did. I bought some TV twinlead (that stuff with two wires separated by insulation), one of those TV balun things, and a TV coax to BNC adapter. I cut the twin lead to 52 inches, then twisted the two wires together at each end. Then I cut one of the wires in the center and screwed the two leads to the balun. Then I attached the balun to the BNC connector and hooked it up to the radio. The improvement over the rubber duckie is very apparent.

I also toyed with just hooking one lead of the original 6-foot length of twin lead directly to the center of the coax/BNC adapter. This also works well (I presume this is a random wire antenna), and you could probably also use a coat hanger. This would make a good portable antenna for visiting the airport. Look, two antennas in one!

Here’s some techincal tidbits about the antenna I made. 52 inches corresponds to 108 MHz. I will probably trim it to 122.7 MHz (KLRU CTAF) when I get home, but I wanted to err on the side of too long to start with. A folded dipole is 300Ω balanced, and my scanner wants a 50Ω unbalanced connection, which is where the balun comes in. It converts to 75Ω unbalanced, which is still not a perfect match but seems to work well enough. I have since found plans for what’s called a “coaxial dipole”, or “double bazooka” antenna, which claims to not need a balun and match 50Ω. There are also plans for a twelfth-wave matching transformer that will match 75Ω to 50Ω with about a foot of coax, but you need both 50Ω and 75Ω coax to do it. The cost of that could be a few cents if you have spare coax lying around, or $20 if you have to buy it new. If I have unsatisfactory reception at home, I may try the bazooka and/or the transformer and report.