Continuously Deformed Antenna Challenge
Dan (N3OX)
on
April 16, 2008
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Announcing the N3OX Continuously Deformed Antenna Challenge! Sparked by a recent thread in the Elmers forum, I propose the following homebrew contest: Start with a perfectly good half-wave dipole, and turn it into a shortened antenna subject to the following rules.
1) Original dipole should be trimmed for a center frequency of 14.200MHz at the desired installation height.
2) The original dipole must be continuously deformed into the new antenna. In other words:
a) No metallic self intersections. You can fold back or wind up as tightly as you want as long as nothing shorts out via a direct conductive path. You can be creative... you can wind inductors, whatever, but don't short anything out.
b) No cutting. (There is one exception, will discuss later)
3) Electrically insulating supporting structures can be added freely, but should not substantially alter the electrical characteristics of the antenna vs. if it were built in free space (in other words, no fair using high dielectric constant stuff to resonate the antenna)
4) The finished shortened antenna should exhibit a 1:4:1 or lower SWR on 50 ohm coax at a single spot frequency (+/- 500Hz) in the 20m band.
5) The feedpoint may consist of any two points on the antenna but only 3" of additional wire outside of that present may be used to make connections. So, for example, you may bend the central part of a wire into a matching stub, and connect the coax across that stub. This is consistent with the "continuous deformation" rule.
The only exception is that you may join the original dipole's feedpoint gap with solder and open a cut at another place to insert a series feedpoint if that is what your antenna requires.
6) A good choke balun of at least 1000 ohms impedance must be installed at the antenna feedpoint for testing.
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7) Entry categories are:
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Three-Quarters Size *
Half Size *
Quarter Size *
Eighth Size *
Sixteenth Size *
Worst
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The antenna with the least loss compared to the full size dipole is the winner in each size category.
The size for the size based categories should be measured between the two points furthest apart on the antenna wire, and for the purposes of this competition, we'll call a full-size 20m half-wave dipole 34 feet long.
The winner of "worst" is simply the worst radiator that incorporates 1/2 wavelength of wire, continuously deformed, but still shows a 1.4:1 or lower SWR at the feedpoint on a spot frequency on 20m. Air core toroidal structures are probably a good bet here ;-)
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OK, I'll admit, it's kind of a joke, but if you *did* want to try it and sent construction details, test results vs. a dipole, and a sketch and/or photo to n3ox.dan@gmail.com (or on paper to my address as listed at QRZ.com for scanning), I'd sure be happy to write something up on my website for everyone to enjoy... or if there's actually significant interest, I'll post a follow up article on eHam. Let's say entries must be received by September 1st, 2008 (giving us all summer to play around, and extensions will be granted if it takes 3 months for this article to post!).
But mostly... it's just something to ponder and discuss. What's the BEST and WORST way to deploy 1/2 wavelength worth of wire in a small space ? There are lots of ways to do it. There's nothing magical about 1/2 wavelength of total wire length, but it so often seems that shortened antenna manufacturers and designers try to stuff that length in for, maybe, marketing reasons, so I'm running with it!
So, let's discuss it and, heck, let's try it.
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RE: Continuously Deformed Antenna Challenge
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by N3OX on April 16, 2008
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I should have added to the article that the truly *useful* antennas will have the widest bandwidth for their size and gain... so we should measure 2:1 SWR bandwidth too... but when I wrote it I was thinking not about *useful* antennas but about ones that you could market as being "almost as good as a dipole" even if it was at a spot frequency ;-)
Dan
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Continuously Deformed Antenna Challenge
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by KB2DHG on April 16, 2008
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YOU PEOPLE HAVE WAY TOO MUCH TIME ON YOUR HANDS!
WOW sounds like fun and a real challenge, I just wish I had the time to try it!
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RE: Continuously Deformed Antenna Challenge
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by K0BG on April 16, 2008
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Well, the king of the hill, if they choose to enter, would be Firestick. Those folks openly advertise a 3 foot long antenna, with a 5/8 length of wire wound around it, which exhibits gain! Apparently, Dan, they know something we don't. Perhaps they're better at the fine art of braggadocio.
Alan, KØBG
www.k0bg.com
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Continuously Deformed Antenna Challenge
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by N0EW on April 16, 2008
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How about deforming them to the point you are _not_ even permitted to use metal wire or metal pipe?
No, wait a minute, we already do that in the K0S Strange Antenna Challenge each Memorial Day holiday weekend.
;^)
Erik n0ew
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Continuously Deformed Antenna Challenge
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by N0EW on April 16, 2008
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I'd consider limiting the height too. Perhaps make it a NVIS project and keep the feed point height above ground between 0.1 and 0.2 wavelengths. Or go the other way and state a minimum height of 0.25. Or have 'classes' based upon such height thresholds.
Unless, of course, you wish the effect of changing height changing the feed point impedance. That is certainly one way to 'tune' an antenna.
As to the 1,000-ohm choke, you should publish a construction/verification sheet discussing the proper construction and measurement of the end-result impedance. Keep everyone on the same sheet of music.
What about coax type/length restrictions? 50- or 100-foot of RF-174 is sure going to drop that swr down!
What about the RF envelope and intended areas of illumination? Or is that going too far, too soon?
Certainly the underlying idea is a good one: To experiment with antennas. One of my local clubs has regular Antenna Parties, about twice a year it seems like. You never really know what people will bring in as a problem/project. It is very interesting.
73-Erik n0ew
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RE: Continuously Deformed Antenna Challenge
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by N3JBH on April 16, 2008
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Wait one minute here Alan !!! you mean that four square array i made using 75 meter fire sticks won't have 47 Db gain? Then dirty dogs !!! Ok folks i realy did not do that. Jeff
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RE: Continuously Deformed Antenna Challenge
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by KL7HF on April 16, 2008
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We used to have contests at hamfests where each
contestant brought a radio and lots of aluminum
canned beer and sheet metal screws.
The winner was the group who drank enough beer to
allow the cans to be screwed together and attached as
an antenna - and then made a single contact.
The first part of the contest was boring. Then it
became more and more exciting.
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RE: Continuously Deformed Antenna Challenge
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by KL7HF on April 16, 2008
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By the way - quite often nobody won.
But, then again, nobody lost!
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Continuously Deformed Antenna Challenge
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by N0AH on April 16, 2008
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Why do I invision one of those Super Bowl ads with the chimps making antennas instead of being in the board room here--
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RE: Continuously Deformed Antenna Challenge
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by N3JBH on April 16, 2008
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i think there allready is a winner in this contest WA2TAK. http://www.tak-tenna.com
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RE: Continuously Deformed Antenna Challenge
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by N3OX on April 16, 2008
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N0AH, Everyone knows chimps will just put up a simple dipole.
They've got lots of trees, and are busy enough trying to survive against ecological pressures to form HOA's, so they don't have to mess around.
;-)
Erik, N0EW, good points about contest standards... though I wouldn't necessarily want to limit the height. As a real, practical antenna matter, it's almost certainly better to have a half-size dipole with -1dBd gain at 50 feet than to be stuck with a full size dipole at 25 feet... the height gain makes up for it. You know, if a four foot loaded dipole that looks like a HDTV antenna up on the roof beats a full size dipole on a 6 foot privacy fence, I'd want to allow that !
KB2DHG, I'm hoping *I* have time to try... ;-)
Dan
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RE: Continuously Deformed Antenna Challenge
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by N3OX on April 16, 2008
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Gee, Jeff, I think you may have found my muse ;-)
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RE: Continuously Deformed Antenna Challenge
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by KJ4AGA on April 16, 2008
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I bet you I could take the best instructions from the internet and end up with the worst antenna....even after following it to the "t", lol, thats just my luck.
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RE: Continuously Deformed Antenna Challenge
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by K6AER on April 16, 2008
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I just looked through the AES catalog and quite a few antennas would qualify. Especially in the worst category.
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RE: Continuously Deformed Antenna Challenge
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by AA4PB on April 16, 2008
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The winner was the group who drank enough beer to
allow the cans to be screwed together and attached as
an antenna - and then made a single contact.
-------------------------------------------------------
Drink enough beer and you'll swear you measured 47dB gain.
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RE: Continuously Deformed Antenna Challenge
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by N4JTE on April 16, 2008
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Darn, we've all been told that length, angle of the dangle etc, doesn't matter, and now Dan is about to scientifically disproove all our comfortable, well entrenched, marketing and researched validated beliefs. Oh, forgot, this is about antennas.
Carry on Daniel, hi
73
Bob
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Continuously Deformed Antenna Challenge
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by W4YJ on April 16, 2008
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Arggg..... we need ANOTHER contest like we need a hole in our head. Their are FAR too many contests as it is. All they do is clutter up the band with over modulated, over processed signals.
Steve W4SEF
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Continuously Deformed Antenna Challenge
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by N9ESH on April 16, 2008
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Is it permissible to perform this challenge to someone else’s antenna, without their knowledge? You see, I have this neighbor who's a free band Cber…..
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RE: Continuously Deformed Antenna Challenge
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by N2UGB on April 17, 2008
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G3MOJ has instructions to make a six, that is six-inch center fed antenna with very specific lengths of twin lead. I think his home page is listed.
Would love to see the on-air results of this thing. I have the impression that the twin lead is the actual antenna.
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RE: Continuously Deformed Antenna Challenge
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by WW5AA on April 17, 2008
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Dan,
It works great...converted it into a mystery antenna. Then into a G5RV and finally achieved the most gain by rolling up the radiator and coax into a five gallon bucket with mineral oil...1:1 and I can work any station I hear.
73 de Lindy
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RE: Continuously Deformed Antenna Challenge
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by WA2NHZ on April 18, 2008
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I've built and used these successfully on Echolink.
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Easy enough....
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by KE4PTM on April 19, 2008
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End Fed on 20 meters:
Using #12 or fatter wires take a half wave and put it up as high as you can get it. Take a quarter wave and do the same but stack it a foot or two right underneath the half wave wire. The 1/4 wave wire has to be within just a few degrees of the top wire or else the reflected power specs will start to increase.
Feed the ends into a 6:1 current balun and use any
decent coax (RG-8x or better). The antenna is essentially a J-Pole laying on its side with a 1/4 wave missing. The one I have here has 2:1 SWR bandwidth of nearly 2.5 MHz (that's right, MHz). The antenna's power handling will only be dependent upon the balun you use. I have put 1.2kW into this one and the specs don't change.
Upon modeling the design in EZNECv5 I found that, for the height (15' above fairly lossy Florida sand), it has the same beamwidth and takeoff angles as a 1/2 wave center fed dipole. It shows only 0.2dB of loss over a same height classic dipole as well.
Decent specs? The proof is how good it works. I have worked most of Europe, South America, and most of the
states with it using only 100W much of the time. With a
decent manual tuner it will also function on every band above it.
If finding a 6:1 balun is a problem, you can
shorten the upper half wave portion by a third, string it through 450 Ohm ladder line that is around the same length as the upper wire was shortened, connect one end to the wire, the other to the coax center or a 1:1 balun (any type). With a bit of trimming of the wires and ladder line it will work. The only problem with this design is that the 2:1 SWR bandwidth narrows to around 350 kHz and it becomes trickier to tune other bands.
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RE: Continuously Deformed Antenna Challenge
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by N0EE on April 19, 2008
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Metal wire? Is there another kind? I know there is plastic pipe but... Sorry, just couldn't help it!
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RE: Continuously Deformed Antenna Challenge
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by N3OX on April 22, 2008
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"??WHY?? would I want to do this?"
Yep, that's kind of the question I want people to ask.
Why put a bunch of time and effort into turning a perfectly good dipole into a different structure that happens to be resonant at the same frequency?
Can you make it better by doing this? Can you make it adequate for its size?
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RE: Continuously Deformed Antenna Challenge
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by K1KAA on April 23, 2008
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Well, the key here is to build a seriously deformed antenna, and just put the center at the top of 100' of aluminum hihi
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RE: Continuously Deformed Antenna Challenge
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by W4LGH on April 23, 2008
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Again I ask why???
There are already enough seriously deformed antennas on the market now. Like the any of the GAP antennas, Hy-Gain, Cushcraft, and lets not forget the super seriously deformed antenna designs from MFJ along with their 1.5x1.5' grounding plate/antenna base for their seriously deformed antennas.
I have argued til I am blue in the face, that it only takes a very little amount of RF to be radiated into space and get a good signal on the other end. People using lossy feed lines, antenna tuners in their shacks going to some ramdom lengths of wire and thinking they have a great antenna system. That reflected power ratios mena nothing, as it will bounce back and forth until it radiated, BS. True its not as big a deal as some make it out to be, but the least amount reflected the better, however so little it may be better, but Better is still Better! Deform away!
73 de W4LGH - Alan
http://www.w4lgh.com
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RE: Continuously Deformed Antenna Challenge
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by N3OX on April 24, 2008
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But Alan, one of the requirements here is that the antenna be *resonant and 50 ohms* somewhere in the band.
You can certainly get behind that, right?
;-)
Dan
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