The Fugue

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.

Last night somebody broke into and/or vandalized cars in our parking lot. My
car was halfway across the parking lot (big church parking lot behind our
apartments) but otherwise unvandalized. I say unvandalized, but not unrobbed.
They took my car radio. It looked like a CD deck, but as they will no doubt
discover the CD deck doesn’t work. I hope they enjoy it. I’m glad my car is
easy to break into (did I even lock the doors?), or I might have smashed
windows like the nuns in another apartment did. If the clowns made any big
mistakes it was smashing the windows of a nun car. Hopefully they’ll be caught,
but I’m guessing probably not.

In any case, we’ll probably replace the radio with something low-end (as this
one was, which might explain the inoperative CD player). When I bought the
solen one, I had to search high and low for one that was cheap, played CDs, had
a knob dial (instead of +/- buttons), and had an auxilary input for my mp3
player. The aux input was the hardest thing to find, so it was a bit of a
trick.

I just browsed Crutchfield and I’m pleased to see
that just about 90% of the decks (even the low-end ones) have aux input, many
on the front. The only thing I need to watch out for now is not to get
something that only works with iPod, and that knob (most seem to have knobs
these days too). Aux inputs on almost all car stereos; now that’s progress.