Steve Ball (Hamster) and I started out by buying the materials necessary to build the antenna. Our first stop was at an electronics supply store in Santa Fe. They salesman provided us with some prices for the feedwire. LM400 provides the best cost/performance. It turns out that it would be about $60 for 50 feet of cable. That's not including the ends which would be about $12 a piece. So we were looking at $168 in cable. No thank you! After we left there we went to the hardware store and bought the PVC elements. One of the problems we ran into was that the 6" outer PVC piping wasn't easily available.
With the parts bought it was up to me to build it. Before I was going to do that I wanted to become very familiar with the theory behind the antenna. It turns out that I had forgotten most of my antenna theory that I learned when I got my ham radio license. The ARRL Antenna book was very helpful. I downloaded the hexicalc program from Jason's webpage and tweaked it until I got it working in a way that fit with what we needed to do. Then I verified the equations manually using the ones that are listed in the ARRL antenna book. There are several things that are important to building such a high frequency antenna as this one. The first is that the characteristics of the line feed are very important. Most normal RG-8 feedlines are not adequate for the frequency range. The LM-400 described above is what the industry standard calls for. After a bit more inspection, we found that Belden 9914, a type of RG-8 cabling, has the gain/loss characteristics we were looking for. At 10db loss per 100 foot, our requirements of 50 foot of cable would only result in 5db of loss. The next issue is the end connectors to be used. N-Type connectors are very important as they minimize the loss at high frequencies. As a matter of fact, the loss for a standard PL-259 connector in the gigahertz range was so high, it was very likely that would stunt the whole project.
We've run into several problems while building the antennas. The first was that we weren't expecting the feedline to be so expensive. The next problem we ran into was finding N-type connectors. Los Alamos is a small town. Unlike most towns there is a large highly educated population living here. One would think that the Radio Shack would know what an N-type connector is. They didn't have any, but that didn't stop them from trying to sell me a stereo.
Luckily there is a Museum of Nuclear Waste in Los Alamos called the BlackHole. A man named Ed Grothus is the propreitor of this treasure trove of forgotten electronic equipment. Among the novelties there are nuclear detonation wire, 100 caliber bullet casings, and old Sun equipment. I digress. What we were after was some low-loss, high-frequency (4 gHz) cable. He had most of what we were looking for. The N-type connectors were there, as well as some Belden 9914 cable. This cable has about 10db of loss per 100 feet. Since I only needed about 50 feet of it, that was an acceptable loss of 5db. The only things that we did not find were the male-female n-type connectors. There was cat poop all over the antennas, which is another story by itself.
UPDATE 4/22/03
As it turns out that Belden 9914 doesn't work for crap at the 2.4ghz range. (Roughly 20db of attenuation at 100 feet...yeek!) We're in the process of getting some LMR-400, hopefully at a better price than what it goes for new. $1.04/ft is steep.
Here are some pictures of the latest round of work:
Helical Winding
Reflector
Initial Assembly
WAP-11 Outside In a new box. (Shhh!) Don't tell the Linksys warranty department.
The Linksys WAP11 has a small type of connector called MCX. We need them to go to a female type-n connector. To do this Steve contacted a company called Fab-corp. Once those come in, we'll be able to wire them up and see how well they do.
