Making the Ground Plane Antenna Tunable

While I’m still seriously considering putting up a a beam, I’m having a fair amount of success with my simple ground plane antenna. The biggest problem with the ground plane, though, is that I’m limited to a single band–20m–and if 10m is open, there’s no way for me to get on. It’s also not a very robust installation; this is something I’m going to have to do something about sooner or later.

So, this got me to thinking about how I could improve the antenna. One thing that would be simple to do is to make it usable on 20, 17, 15, 12, and 10 by making the lengths of the elements easily adjustable. Since the antenna is currently made of wire, I was thinking of some kind of reel mechanism to shorten the elements. That would work, but it wouldn’t do much for the robustness of the antenna.

Then, I thought about using aluminum tubing. Tubing would not only make the antenna more robust, but perhaps also improve the bandwidth of the antenna. A quick search of the eHam forums turned up a discussion on where to buy the tubing.

Each element would be made up of two or three pieces of tubing that would fit into one another. To change bands, all the user would have to do is slide the pieces in or out to the appropriate length. To make tuning quick and easy, the user would mark the antenna with either a permanent marker, or if he really wanted to get fancy, with some kind of label.

One thing I haven’t quite figured out how to do yet is how to terminate the elements and connect them to a coax connector. With wire, it’s pretty easy to do. With aluminum tubing, less so.

Yet Another Idea
In the April 2003 issue of QST, the Hints and Kinks column had an item titled, “A Push-Button Memory Antenna Tuner for $2!” Written by W0FM, this item describes how he uses cord stoppers, those spring-loaded plastic or metal thingies used to control the length of drawstrings, to adjust the length of dipoles. I think this could also work quite nicely for the ground plane antenna.

I’m going to buy a package of cord stoppers and play around a little. As W0FM points out, it might make a good Field Day antenna.

Comments

  1. Have you ever tried the Antenex Laird B8965C No Ground Plane Closed Collinear Antenna, 896-970MHz Frequency, Tunable Center Frequency, Chrome Color, 5dB Gain, 16″ Overall Length (B8965C B-8965C B 8965C). I was thinking about a purchase or is their a better one out there?

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