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Yagi Antenna







YAGI ANTENNA

Sounds like a movie title doesn't it? It seems since the advent of computer software primarily Eznec, there are legions of relatively new experts all claiming to have a better way to build a Yagi antenna. Some of these are quite good actually, and some will have you making something that half way through building it your going to be wondering why you got into this hobby in the first place. Just to reiterate I like Yagi antennas and in most conditions they do a wonderful job of getting you to places you will never be able to talk and listen to. Most Yagi antenna are quickly built yagi antennas. However some Yagi antenna fans not content to sit on their laurels ( and why should they? ) have been busy coming up with scheme's to build a better antenna. Now let me say this: Alot of these Eznec experts (I do really mean they are experts) I speak to quite frequently either through email or on the phone. And I frequently even buy their designs and try them out myself! And I am certainly interested in all antenna designs that will affect my own primarily HF recieving performance. However:

Doesn't this look fun to build? maybe on 432 mhz and when you have alot of time on your hands, and even more to model it. No thanks.

Or how about this one? Lots of elements surrounded by smaller ones? let's turn a 8 element yagi antenna into a 24 element yagi antenna! Why not! All of this and believe me there are many more designs that are based on the same principle........ Turn a single yagi beam into a stacked version (normally two yagi antennas) without building a whole nother yagi antenna. If you are familiar with Eznec you have noticed that these designs are trying to accomplish the same thing, isolate two yagi horizontal sections by providing a way to kill the radiation in the mid section of the antenna. In effect build one yagi antenna with the gain properties of two stacked yagi antennas. If even they are not exactly stacked at a long enough distance, or are compromised a bit on the bandwidth. What does this sound like?? And what is the visual description of what they are trying to accomplish? Have a look below.



But wait a minute, thats a Cubical Quad ! Correct ! Yagi antenna experts have for years complained that the Cubical Quad was just two 1/4 wave elements stacked one above the other. Thats right it is. Has anyone ever complained having two stacked yagi's? So what's wrong with having two stacked antennas?? Apparently nothing nowadays, as long as we call it a (place name here)Yagi antenna. My point is, all of these designs are trying to accomplish the same 1 - 1.8 increased DB gain as the Quad. So I ask you? Which looks simpler to build? The designs shown at the beginning of the page or the Quad shown directly above? Some of these newer yagi designs use elements that are a 1/2 wave long or longer, for increased gain. Sounds good, but do you really wanna build one of these? Especially on HF? Really?



Again I am not deriding anyone's work in antenna design, lord knows I have made my share of design Edsel's over the years. But adding unnecessary complexity, weight and not to mention trying to accurately match these designs in the REAL World. I just don't see much benefit for the extended effort involved.

Traps vs No Traps

Trap Antennas

Antenna Traps

So lets say no matter what I tell you, you are not putting up a cubical quad antenna, but would like useful information about putting up a yagi antenna. Okay fair enough. There is also some decent information on the EZnec page on Yagi Antennas, but lets assume you just want a modern decent high gain Yagi Antenna. What should you look for? There is some confusing information about Yagi antennas online and even written in technical articles and psuedo test books. Most of this involves the use of TRAPS. Traps are attempt by manufacturers to make shorter antennas by using wire wound around and non metallic cylindrical tube just below the resonant frequency of the desired frequency. This was invented by Mosley antennas so they can make shorter multiband antennas. The first trap is the highest band, and a bit farther out on the antenna will be the band slightly lower then that, and this continues until the last trap which is the lowest in frequency band needed. Generally no more then 3 traps are used on one antenna radiator...HENCE : The Tribander. Some amateurs hate traps and they have a controversial reputation. But should they? One reference claims that trapped tribander antennas with booms up to 25 feet long are no better then a half wave dipole THIS IS BLATANTLY FALSE. Another reference that one Specific manufacturer of trapped antennas (Mosley antennas) is terrible and all their antennas are poor performers. THIS IS BLATANTLY FALSE. So how efficient are they? It turns out that depends on the traps the manufacturer uses. My experience with antenna traps, is they do require maintenance, some bugs and dirt will get inside of them and that with the weather over time will degrade their performance. But how efficient are they you ask again? Turns out pretty efficient overall. I can verify traps made by Mosley antennas and Hygain antennas are very good overall. If you are using any Yagi antenna from 17- 80 meters, mostly likely it is not full size and uses some sort of traps or linear loading or some other buzzword to make up for the shortened elements that you are using. Don't worry about Traps they are for the most part efficient. They will require periodic maintenance once in a while and don't blast them with excessive wattage and you'll be happy with them. Mosley Antennas are good examples of quality trap antennas, no matter what you've read.

How they work and don't worry about loss

Thanks go to Roy Lewallen for his wonderful EZnec program, which helps give an accurate picture of trap losses

Without trying to get too complicated, here goes: With traps the big buzzword is "Q". The higher the "Q" the more efficient the trap is. Well built antenna traps made by the above mentioned manufacturers are of high "Q" design, and these should only have a loss of .1 to .2 db loss per trap versus and full length antenna radiator. So whats this "Q" all about. Basically the "Q" is the amount of electrical energy that comes into the trap versus how much comes out the other side. 100% in 95% out.... kind of analogy. You can even make traps out of coax wrapped around a PVC tube! However my experience is these coax traps do not have a very high "Q" (400), they are probably close to .5 db loss per trap versus a straight no trap full size dipole. But they do work. Are manufacturer made trapped antennas good antennas? My answer is yes. Now that doesn't mean you should believe any of the db claims in advertising anymore then you should believe anybody else's claims. Can trapped antennas provide more gain then non-trapped full size monoband antennas ? NO. Its not possible. Traps cannot increase gain only lose some of it. If you can put up a full size monobander and thats all you want at your location, by all means choose that over a trapped antenna. But if your like many amateurs and do not have room for lots of big antennas and or towers, then a trapped tribander or other trapped antenna type will work just fine. Can you get an idea of trap losses without depending upon software? Sure, grab a trap after putting some power into it after a few minutes of transmitting in the shack, and see if it got warm. This is where any losses will go. My bet is you won't even be able to feel any difference between it and the outside temperture. This indicates very minimal losses. So why do some people abhor them. Traps are like tuners, they DO have power ratings, maybe some people after much work finally put up their large tribander, and then decided to put A Gazillion watts through it. It blew up, they took it down and said " traps suck " . And that was that. I am sure that is some of it.

Other bad info touted is by amateurs building their own designs and therefore the "trapped" antenna becomes an easy target to pick on. What about those "tests" made by amateurs saying trapped antennas suffer from "blah, blah ,blah, etc, etc" and they should be avoided like the plague at all times by any manufacturer. What can I tell you? Traps are not that difficult to understand or build. They are basically similar to loading coils (with an added capacitor) and loading coils are used on virtually every HF mobile antenna. And nobody complains about them there. There is alot of anti-trap propaganda on the net, avoid it when deciding to purchase the multiband antenna that fits perfectly in your yard and allows you to use bands you don't have good antennas for now.

Ok enough about traps, what about the newer Yagi antenna design ?

I would default to EZnec as that can teach you alot about antenna design, but generally the Yagi design timeline looks like this:

1. For many years the Yagi antenna types were wide evenly spaced designs, matched with some type beta or gamma match.

2. Trapped designs came in that meant you could have multiple bands per antenna. Fed with one piece of coax usually.

3. Then basic computer programs showed that Yagi's could be matched with sections of 75 ohm coax runs to then get to a 50 ohm impedance.

4. Then you could eliminate any of this, by resizing the elements on the fly and get good SWR ( Steppir and Ultrabeam antennas)

5. Further computer advancements in modeling showed that monoband Yagi's could be re-spaced and resized to give good results while just using 50 ohm coax.

6. As more adventureous amateurs became involved with computer design, multiband designs came up with element spacings very close to one another to "create" 12 meters or other frequencys where no 12 meter or other frequency antenna driven element is even present! 7 bands, 15 elements all on a 11 foot boom all fed with one piece of 50 ohm coax. Some of these have fantastic DB gain claims. Don't believe them. I DON'T

7. UHF experimenters claim the best Yagi's are ones with the lowest noise ( best front to back and front to side ratios ). And any of the above designs are immaterial.

For me and what I have seen personally. I have used all of these. AND #5 and #7 gave me the best performance. Its tough to beat a properly spaced and tuned Monoband Yagi with any other Yagi "Improved" design like #6. Can you put lots of elements on a short boom yagi and get all bands with one piece of coax? Will it work? Yes, Will it come anywhere near a single Monoband Yagi of a similar or greater boom length? Absolutely Never. At least not now it doesn't. With these designs you end up with either smaller amounts of real elements, and every band winds up being the equivalent of a 2 or 3 element yagi at best (similar to a log-periodic antenna), because none of the bands are using the full boom length of the antenna only parts of it on any of the bands. When you could have had a 4 or greater element monobander or tribander trapped that works just as well or better. But Wait manufacturers say they work alot better then all of the other designs. Yeah. manufacturers and amateurs claiming to be manufacturers say alot of things. The jury is still out on them despite claims that they do.

The biggest difference in Antenna Gain in a Yagi Antenna or a Cubical Quad for that matter is boom length PERIOD. No matter what kind of voodoo the antenna designer or manufacturer promises you, antenna boom length is the be all, end all of antenna db gain. This goes for Trapped Antennas, Linear Loaded Antennas, Monobander or Multibander Antennas of any type. If they don't increase the actual boom length of the antenna, even if it has Pamela Anderson sitting on it, while its turning around in your backyard, it doesn't have any more gain. Now for me personally I don't care what an antenna is called. If a single monoband Yagi gave 1 - 1.5 more DB gain then a comparable Quad, I would using them no matter what you wanna call it. Yagi, Quad, Quagi, etc,etc. So be aware just like wire antennas, (see 140 varieties here) there are lots of Yagi antenna designs, some good, some ridiculously hard to build, some simple and some completely ineffcient. Antenna's are enough of a pain in the *ss to begin with, in my book I want something simple that works.

Do you want to build a simple yagi yourself?

This Yagi calculator will give you the dimensions you need.

Click on this link and input the frequency you would like