12-29-2010, 01:57 AM
Is this an admission that the 3 element fractal images I discuss above are not an actual fractal antenna?
Originally Posted by W1YW
12-29-2010, 07:43 AM
Originally Posted by W6EM
I don't really want to discuss anything about whether or not the antenna in the photo is real. I have no reason to doubt that it's an actual three element fractal quad. But whether it is or isn't is really beside the point.
There's plenty of information in this thread to try to build some kind of fractal loop antenna if anyone actually wanted to do so. We have KF7BS's article, Chip's pictures, and some of Chip's statements about the pictures. it's pretty clear to me that the antenna in the photos has three elements, planar ones, that are loops of wire that look like this:
That loop fits inside a square that's 1/8th wavelength on a side according to Chip's post with the 3el picture, and parasitics are just a little different in size. That's sufficient information to build and test a multielement beam if one is a very patient tweaker. Not much different from empirically building a regular three element quad aside from all the bending. If I were going to experiment in real life, I'd start with a single loop and test it as a starting point. Easy enough. Try it against other antennas that fit in the same space. Shortened dipoles, etc. Compare model with measurement.
And we don't really have to guess much to build one particular 10m version, given that there's this article on Scribd by KF7BS that has dimensions. I put a single 10m loop from KF7BS's article into EZNEC. I didn't have the patience to "build" a two element model by adding 0.125 inches to each segment... but I ended up with something similar by scaling the reflector by 2%.
Here's some output:
Gain and pattern are for free space, and include wire loss. Efficiency with aluminum wire is about 90%. The lossless model has slightly higher than unity average gain (1.01, 0.06dB). The model seems somewhat sensitive to segmentation at the low end (a few segments between bends), but it seems reasonably well converged with changes to 700,900, and 1300 total segments not changing the gain more than 0.2dB and the F/B more than about 1dB.
I'm pretty confident that if I built this thing, it would be a pretty good small antenna. Is it the best? No one can answer that question. Is it good? Seems that way to me. Could a conventional loaded yagi design with loading coils and end hats be better? That's testable.
Would it be preferable for other folks to build something that was just some bent wire, even if some coils and tubing did a bit better? Quite possibly.
Does "fractal" make it better? I don't know. But there are a lot of people posing a lot of untested ideas about what would and wouldn't be better. So try it. There's plenty of information right here, right now on QRZ to experiment with some version of small fractal antennas. It would be very nice for home builders to have exact dimensions to follow.
But it's not really necessary to have those to test some of the hypotheses that people have raised in this thread (it's a dummy load, it's no better/no different than other types of foldy-loading, etc). There's plenty of info here to do that if someone wanted to.
12-29-2010, 11:02 AM
Hi to all
Happy new year!
Some time ago I was looking for info about fractal antenna. I find out that W1YW is actualy owner of article from 73 magazine. Also I find out that 10m Quad is no longer in sites.
I am not involved in antenna design so I wonder to see how other made antennas.
Unfortunately now this antenna are made by a company and sell around. No realy info to find. I understand that they make bussines with it and take care about knowledge. If some one can make a .jpg or .pdf copy of 73 magazine where are the description of antenna I will say "thank you"
About N3OX remarks. It is very good one.
Also the ideea to buy an antenna is good choise. Not every one have acces to the full equiped laboratory to make measurement to antenna, and if you want to rent such place, I think, it is a fortune!
So let spread info about what we have to other how do it.
I like to play with antennas. I think is a one place where we can do something. And can see fastly the result in realy condition.
When you have only one antenna it is dificult to say what antenna is the best. Usualy what you have is the best.....
See you in 2011 with good infos
12-29-2010, 01:11 PM
Originally Posted by AB8MA
Antennas radiate because of the current distributed over a linear volume of space, NOT because of conductor length.
As a matter of fact packing more conductor length into any optimum volume of space for an antenna only results in increased losses and heating, not more EM radiation.
Heating elements and heat exchangers are often spirals within spirals because the goal is to transfer as much heat as possible. Efficient compact antennas use the shortest possible conductor length and have the most uniform current possible along a given spatial area.
A good antenna engineer understands it is where the current is placed in space, and the phase of the current over that area, that makes a good antenna. A good engineer also knows the more conductor length packed into the system, the LEAST efficient the system is.
This all reminds me of an almost cult-like following or religious experience. Like the old rules of nine, astrology, or numerology. Like all the other quackery science, we now have fractology. :-)
12-29-2010, 02:10 PM
I responded in such a way to point out that **critical discussion** is and has been ignored.
Originally Posted by N3OX
Yes, the planar nature is obvious. Now, for the "devil in the details."
There's plenty of information in this thread to try to build some kind of fractal loop antenna if anyone actually wanted to do so. We have KF7BS's article, Chip's pictures, and some of Chip's statements about the pictures. it's pretty clear to me that the antenna in the photos has three elements, planar ones, that are loops of wire....
Either the photos have been "doctored" or the spreaders are four pieces of aluminum that are welded or clamped to the boom. I'm not going to repost the photos, so go back and look for yourselves. Insulated spreaders are necessary, obviously, to avoid distorting the fields created by the driven and parasitic elements.
If one looks at the length of each spreader, they would be just under 3 feet, assuming the FQ is 1/8 wavelength on a side using a little trig.
Since the spreaders are in the same plane (planar) at the boom, they cannot pass through it as continuous pieces. Therefore, they must be clamped or welded. Ah, but they COULD be fiberglass or plastic of a gray color, looking almost like the aluminum boom. OK. Ever used any fiberglass? Or, plastic rod for that matter? Both are extremely fragile with significant torque or moments applied to a very short end point support. As in, they'd easily snap off. Normally sized quad spreaders are a good example, as they are usually a cast-aluminum cross, with enough length to support the fiberglass rod far enough that it can take the torque/moments without failing.
So, the planar nature of the spreaders and the fact that they literally appear to be within a fraction of an inch of the element wires, lead me to believe that if the antenna is real, it has some significant issues. Besides the fact of the lighting in the oblique photo being quite unusual, what with a moon indicating sunlight from the left, yet illumination in the photo coming from the right.
Perhaps, indeed, it IS a real antenna. And, maybe the photos aren't doctored. For me, at least, it left/leaves many unanswered questions.
12-29-2010, 03:02 PM
Tom, an excellent treatise. One need only look at current distribution on noted excellent antennas or on W7EL Roy Lewellan's EZNEC. Phasing is used, by design, to reinforce or diminish EM fields and achieve gain, bandwidth and directivity.
Originally Posted by W8JI
12-29-2010, 03:02 PM
No. It is a statement that the discussion turned away from antennas to attacks of a personal nature. That is sad.
Originally Posted by W6EM
But then one well known tactic used by people who are losing arguments is to attack the messenger.
I think this antenna does have merits, but still like any other antenna, particularly those that are shortened one way or the other it will have limitations compared to a full sized antenna.
That does not detract from this design any more than any other antenna designed for 'small spaces'.
I think more study needs to be done regarding radiation patterns, etc.
I wish Chip luck.
Ron - KI4TI
12-29-2010, 03:45 PM
I wouldn't call reposting what amounted to a funny incident a personal attack. I did see, though, a remark made by Chip about a couple of "cranks" who are/were thread participants a while back. That was, frankly, a personal attack of sorts, although the specific individuals were not identified.
Originally Posted by KI4TI
If valid questions about what he presents are ignored or go unanswered because he chooses not to, it serves as an admission of their validity. An admission by default, so to speak.
So be it.
Tom, W8JI, is an accomplished antenna designer and knows what he's talking about. Re-read his post carefully.
12-29-2010, 04:30 PM
Recently, I designed and built a fractal antenna for 160 meters. It was about the size of a dime. I took it out to the antenna test range for evaluation but dropped it in the grass and cannot find it. I plan to write a technical article on it and it may be in QST APRIL issue.
Talk about bandwidth....try a 51 ohms non-inductive resistor for that! I will keep you advised...
73 Joe W4CBJ
Professor, Institute of Scientific Humor
In honor of J. Harold Angel WB4IHS/WB4YMC (SK)
12-29-2010, 04:50 PM
Hi, Joe. Happy New Year. Sure wish we had a little of your warmth from west central Florida up here in central Alabama. White stuff still on the ground, but almost gone.
Originally Posted by W4CBJ
Speaking of US coinage and what can be done with it, one of these days, I'm going to try my luck with a penny-cell battery. The mint has been sandwiching copper and zinc for years, so it's high time to make some juice out of them. Don't know if I want to invest in a jeweler's saw or just use sandpaper... The other way might be with a discarded, aluminum beverage can. Although, not sure whether Coke or beer would make a better electrolyte.