Anyone who’s been reading this blog (and I can probably count that number on one hand) knows that I’ve been thinking about a new (to me) antenna design. Being in a covenant-restricted neighborhood, I can’t erect a permanent obvious-looking antenna. But the neighborhood covenants are not extremely restrictive, I have nice neighbors, and there doesn’t appear to be any actual HOA that actively searches for covenant violations, so I figure I can get away with an antenna with a reasonably small visual footprint that I only put up when I want to play radio. To top things off, I have no trees or other readily available antenna supports, so whatever I end up using must be free-standing. The obvious choice, at least to me, is a vertical antenna.
Now, I know I can find plenty of hams who will tell me that verticals are no good–that they’re a compromise, at best. To those poopooheads, I say this: I’ve used verticals before, and I was able to derive plenty of ham radio enjoyment while using them. As far as being a compromise goes, I just say this: well, duh! This whole situation has compromise written all over it, doesn’t it?
Now that I’ve gotten a little sarcasm out of my system, let me start by listing my “requirements”: cover 10-15-20-40, stay under 20 ft tall (probably around 16-17 ft or so), not require a tuner, not require manual band-switching, be self-supporting, and be easy to set up and take down.
The design that I’ve been mulling for the past few months involves using coax traps for 10, 15, and 20 meters and some sort of loading scheme to shorten the antenna for 40 meters–either a loading coil or linear loading (check out the ARRL Antenna book if you don’t know what linear loading is). Certainly, it’s challenging to come up with a design that low SWR and reasonable performance on the desired bands.
Equally challenging, though, is implementing the design in a mechanical form that’s durable, self-supporting, and easily set up and taken down. Luckily, I happened across Phil Salas’ ultimate portable vertical (see it and much more at www.ad5x.com). His design uses commonly-available hardware like half-inch aluminum tubing and various plumbing parts to construct a vertical antenna that can be used all the way up to 60m. I built and used this antenna recently and was very impressed by the mechanical design. The one thing that I do not like is that I have to manually adjust the antenna to switch bands.
At any rate, AD5X’s design gave me some good ideas for how to build my new antenna once I’ve designed it. Designing the antenna is still a major task, and I decided that it was time for me to learn about modeling antennas using software like NEC-2. It turns out that almost everyone uses some commercial package that uses NEC-2 as its computational engine. EZ-NEC is quite a popular choice but costs $89 and up. There are other choices, too, but I eventually found 4Nec2, a free package that also uses NEC-2 and provides some of the same capabilities as the commercial packages. I’ve only been using it for a few hours but so far I’ve been able to create models of simple antennas that appear to behave like you’d expect. Once I figured out what I was doing, it would take me just a few minutes to build a simple model and run it so that I could see the predicted SWR across a band, for instance. If you’re looking to try a little antenna modeling yourself without having to plunk down a lot of cash, I’d encourage you to give this package a try.
So, stay tuned… I expect that I’ll be able to create a model or two over the holidays and maybe be ready to start some construction in the near future.