Experimentation is a major aspect of amateur radio. In fact, the innate learning style some of us are endowed with at birth, requires a hands-on approach, or we just don't get it! Others do very well with nothing more than reading books, while others excel in classroom-based learning. In the real world, the average person's learned intelligence is a combination of all three. Looking at this another way; if you're not endowed with at least a modicum of knowledge (book or classroom based) about the subject at hand, the results from your experimentation will be suspect at best. With that in mind...
Without doubt, the most prevalent experimental theme in amateur radio, and the most controversial, is the ubiquitous antenna. Everyone has to have one is some form another, and God knows there are more forms of it than any one person can imagine. There are dipoles, monopoles, yagis, off-center fed ones, verticals, wires, aluminum ones, mobiles, HF, VHF, inverted Vs, slopers, quads, and even dummy ones. And every single one of them must adhere to principles set forth by Kirchoff and Maxwell. There are no mythical antennas which can violate, defy, circumvent, ignore, or modify these principles.
It's agreed that not everyone is endowed with the capability to understand the aforementioned principles. However, you should have some basic knowledge about antennas just to install a store-bought one. When you don't have the knowledge, you could easily end up dead! At the least, you end up throwing your money away and/or be stuck with a less than stellar sky wire.
The following antenna examples all have a great following. Some users are so enamored with their choice, they ignore the inherent problems associated with them. A few even re-propagate the mythical attributes they're supposedly endowed with, even though they defy the aforementioned principles.
Nowadays, with the aid of modeling software like EZNEC, the masses can learn a lot more about antennas, what their radiation patterns look like, and even their approximate efficiency. Yet the myths about some of them just won't go away! Seemingly, once myths get into print, they obtain gospel status, as if commanded by the almighty. Well, let's look a little closer at some of the more popular antennas, with supposedly mythical properties.
Digressing. EZNEC, and some of the other numeric electromagnetic coding engines, are marvelous programs. They allow expert, and neophyte alike, to model all-manner of antenna parameters. However, the results are dependent on the data provided. For example, leaving out the feed line when doing an analysis will skew the results. Another common error is miscalculating ground losses. Therefore, assuming and quoting the results verbatim, without a basic understanding of how antennas behave, often leads users astray. In other words, they're a tool, not a panacea!
Case One: The End-Fed Dipole
If you just stop and think about the phrase end-fed dipole, the idea just falls apart. If it is end-fed, then it can't a dipole! A dipole is also a balanced antenna, and will technically have equal currents flowing in both poles. In the real world, the balance is not perfect, but is easily handled (using a balun perhaps) so that common mode current on its feed line will be at a minimum.
In the case of the proposed end-fed dipole, the return current must flow back down the outside of the coax feed line, as common mode. Some proponents argue that these unwanted currents can be choked off with a proper ferrite-based choke or balun. Others claim the common mode currents are an asset, allowing the antenna to work better; whatever that means.
One manufacturer openly claims the antenna is multibanded, with a low SWR, even though the fine print says you need an antenna tuner. However, no matter how you cut it, the end-fed dipole is a lousy antenna, fraught with common mode (both ingress and egress), and claiming otherwise reeks in the face of reality. After all, you can't negate the aforementioned principles, no matter what you do.
Case Two: The Off-Center-Fed Dipole (?)
Almost universally, off-center-fed antennas are referred to as Windoms, albeit they have no resemblance to Loren Windom's, W8GZ (sk) original, single wire feed design. Some manufacturers prefix them with the name of a state, assumedly to set them apart from all of the rest of the modified designs.
Remembering that a dipole is an antenna consisting of two equal length elements with a connecting feed at its center, then how can it be off-center-fed, and still be a dipole? Like the misnamed end-fed dipole, the level of common mode current is inordinate. Proponents often espouse the use of a voltage balun in some unorthodox ratio. That might be 1:4, 1:6 or even 1:9, depending on the anecdotal proof of the pudding. About all that happens is, the balun saturates which adds loss, and uncertainty to its already poor performance. Allow me to digress once again.
I have a pet peeve with respect to how ratio baluns are represented in popular text. You often see 4:1 when in reality they mean 1:4. For example; If the feed line is 50 ohm, and we have a 4:1 ratio, then technically the output of the balun is 12.5 ohms. Expressed as 1:4, the input is 50 ohms, and the output is 200 ohms. The situation gets even uglier when you see ratios of 9:1 (5.5 ohm output), when they really mean 1:9 (450 ohms). While a nit perhaps, it is more defining than adding the universally missing verbiage—step up or step down as the case may be—after the expressed ratio.
The actual length of the two elements vary with the designer. To be sure, each one has his/her pet lengths and balun ratio, assumedly designed to negate common mode current and/or enhance some other presumed attribute. Whether or not problems arise due to common mode current (the design notwithstanding), has more to do with the installation parameters, which for all practical purposes are beyond anyone's control. This makes the off-center-fed antenna a true conundrum.
Just for the record, we're not talking about input SWR, which can be mediated to some extent by carefully choosing the lengths of the elements. And, there may be some designs which exhibit low common mode on some bands, but certainly not all, an included balun notwithstanding.
Case Three: The G5RV As An All-band Antenna
There are as many variations of the G5RV as there are variations of Windoms. There are shortened ones, elongated ones, juniors, seniors, and (no lie) off-center-fed ones! Fact is, Louis Varney, G5RV (sk) published several versions himself, both with and without baluns. Someplace along the line, the notion got started that the G5RV was an all-band antenna. Here is a sentence (a verbatim cut and paste) from the web page of one of the companies which makes and sells a version of it: The G5RV is an excellent all-band (3.5-30 MHz) 102 Ft. dipole. The 102 Ft. dipole with 31 Ft. feeder of 450 ohm transmission line achieves a resonance on all bands from 80 to 10 meters with only one antenna without any loss in traps and coils. The impedance at the end of the 450 ohm feed line is 50-60 ohms. No wonder folks are confused!
If you really want to know what kind of antenna the G5RV really is, then here's the nitty gritty, complements of Tom Rauch, W8JI. If you read the data, you'll notice the high input impedance on 30, 17, and 10 meters. Unless you have a very good quality antenna tuner, you might not be able to find a match on these bands. Even then, the overall losses would be rather high. Realizing this, some all-band proponents of the G5RV, suggest removing the coax, and just feed the ladder line directly. When you do this, can it still be called a G5RV?
Case Four: Why 43 Feet?
Within the last few years, the 43 foot vertical has become popular, and available from several manufacturers. Proponents would have you believe the length is special. The truth is, it isn't. The length doesn't assure a good match except where it's resonant. Speaking of which, it isn't resonant across the HF spectrum as one company asserts. Contrary to some advertisements, it does indeed need radials (ground plane), as any vertical monopole does. Further, just because it doesn't have traps, doesn't mean much either. In fact, I suspect a properly installed Hustler 6 BTV will out perform it in any respect.
There's a dirty little secret about the requisite (?) matching balun you don't see in print very often. Most 43 foot vertical antenna sellers recommend a 1:4 voltage balun (always expressed as 4:1). Little if any thought is put into the fact a voltage balun can become a very lossy lump of ferrite when subjected to high reactive loads; almost a given no matter the band of operation.
If you're using a shack-mounted tuner, feed line losses vary all over the board. While tolerable on some frequencies, it certainly isn't tolerable over the whole HF spectrum, balun or no balun, as some pundits claim. Here's a discussion about the 43 foot wonder which appeared in these very pages about 15 months ago. It begs reading if you use a 43 foot vertical, or thinking about buying one.
Case Five: The Quad
Some years back, an article appeared in a popular amateur radio magazine extolling the virtues of the quad antenna, and how much better it was than a yagi, especially at low mounting heights. It further stated the gain was 2 dB better than a comparable yagi; they were less prone to noise reception; and the take off angle was lower. The truth lies elsewhere.
It really doesn't make much difference what the supporting structure is comprised of, be it fiberglass or aluminum. Nor does it make a difference if the elements are DC grounded, used with balun or without a balun, or whether they're in a diamond or square orientation. Their gain isn't any better than a comparable yagi; they're not any quieter than a yagi; and their take off angle isn't any lower.
The only true attribute a quad has (other than they're less susceptible to corona discharge), is their inability to withstand icing conditions.
Common threads in the reviews of antennas universally contain references to DX stations worked, and statements like this antenna just works, or this antenna rocks, and, the SWR is low clear across the band! These statements are nothing more than jabberwocky.
Here's a real-world truth many amateurs will openly argue about: When it comes to simplicity, ease of building, ease of erecting, and ease of tuning, it's very difficult to beat a simple resonant dipole fed with coax. If you mount it correctly, you can actually achieve about 8 dBi of gain. Not too shabby for two chunks of wire, and few miscellaneous pieces of hardware. And you know what? No experimenting needs to be done! Oh. And they really do work!
The best way to combat the misinformation highway, is to spend the requisite effort to learn basic antenna theory, using whatever method is best for you. While experimenting is part of the effort perhaps, it should be based on truths, and not on myths.
When it comes to the printed word, I think Joseph Pulitzer said it best; A cynical, mercenary, demagogic press will in time produce a people as base as itself. To paraphrase; Basing your experimental efforts on myths, and then repeating them ad nauseam, only places you in the same criticizable position as the myth itself.