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Old Geek Invents New Stick
the morgawr writes "According to the EE Times and Science Blog, a scientist at University of Rhode Island has developed a new type of antenna design that, by increasing the efficiency, performs as well as the convential quarter-wave design but is only 1/3 as large."
All i could see is that it is a 2-dimensional helix, so it's likely to be directional, if radio waves aren't hitting it on the perpendicular they will miss.
The other thing I saw was that you tuned the antenna for a frequency with components - does this mean potentiometers or does it mean scrapping it and buying another 2d helix tuned to the specific wavelenghth?
There are several parameters for an antenna system (receive parameters in parens):
Most compact designs trade bandwidth for performance - the work well at f=NNN.N MHz, but not well at f=NNN.N +
This gets to be REALLY important for wide band systems like CDMA and UWB.
www.eFax.com are spammers
Well, nice, but is it better than fractal antennas, i.e. Sierpinski antennas?
No, you're thinking of the VHF FM band...that is exactly the case there.
On the AM radio band the tower IS the antenna. What you see sticking up in the air is usually insulated from ground right at the base, the part you see is actually hot. Therefore the tower itself radiates and is engineered to be a certain height as part of antenna design.
. Quit playing Monopoly with Bill. Switch to one of many non-Microsoft products today.
"I think the actual antenna is attached to the top of the tower. It's not the entire tower. Can someone help me out here?"
Long (LF) and medium wave (MF) antennas usually are the entire tower because of the low wavelength. For VHF (e.g. FM radio) and TV the antenna is much shorter so it is at the top of the tower.
One way to tell if it is not obvious is to look at the steel support ropes. If they are broken along their length with insulators then it is probably a long wave or medium wave antenna. The steel rope is broken in this way to prevent the wire being long enough to become a significant and undesireable part of the antenna.
I wish them well but FWIW, it got a skeptical response on this popular ham site qrz.com
As others have noted, the tower is the antenna. The output line coming from an AM transmitter is fixed directly to the tower. Usually this is not fixed at ground level to avoid killing a passerby. RF waves WILL arc and kill. Also, if you are feeling especially depressed and want to cause yourself bodily harm, walk up to a hot AM tower barefoot and grab it.
As it says in the article, wet (and salty which I didn't know) ground is best for transmission. AM towers are often set in a group of three and set in low lying wetlands (near water especially). If you look closely, you will see that the only thing perched on top would be the strobes (if applicable).
The purpose for the Markland antanna is "stealth" - it can turn on and off and re-tune itself on the fly. It is also a directional antenna. The antenna in this story is a smaller form factor for a wide frequency range omni-directional antenna.
Basically they are apples and oranges.
Kinetic stupidity has a new brand leader: Allen Zadr.
Just to add... since the entire tower is the radiator at AM frequencies, the multiple towers are used for directionality... just like in VHF and UHF (and cell) frequencies, multiple antennae are usually mounted on the towers (though it's tough to see individual antennas since they're usually placed either 1/4-wave or 1/2-wavelength apart... in VHF that would be about 6-10 feet).
So anyways, several AM towers in a straight line (like WEEI, 4 towers south of Boston, or many others - there's a 6-tower set just west of NYC) yield a sort of figure-8 pattern, with the lobes pointed in the same direction as the line of towers... usually an easy way to tell the direction to the nearest big city. There are also directional patterns that aren't so easy, like one of my sites, WRNI in Rhode Island, which has 4 towers, set in a sort of Y shape. 3 are used during the day for one pattern, and one of them turns off and a different one turns on a night for a different pattern.
-T
It should be pointed out that the inventor mentioned in the news release is listed in the Unversity's directory as a "Technician". That is, he is not one of the Physics Department faculty. So I think it highly unlikely that any government funding is involved, or that it will be published. Looking at their website which lists their research programs, in fact, there is no mention of anything having to do with antennas. So in all likelihood this is a bootleg or personal effort, not an official University project. That is not necessarily mean it's bogus - I haven't seen the details myself - so I'm just pointing out that if it does turn out to be nonsense, we should not condemn the Physics department for it!
I am a physicist myself, currently doing materials research for the Navy. From time to time throughout my career, I have been approached by "inventors" with various ideas. I always give these schemes due consideration because, as another poster mentioned, one should keep an "open mind". But mainly because, even if the idea as a whole is nonsense, there may be elements of it that worth something.
There is a pattern. Almost all of the "inventions" that have been presented to me for evaluation and endorsement have made remarkable claims about "efficiency" approaching 100% -or in some cases exceeding 100%. This always turns out to be due to the inventor not recognizing and accounting for all the losses in the system, or making bad assumptions about efficiency being equal to some other factor (there are a few hams, for example, who mistakenly equate SWR with efficiency). There is another pattern to this sort of thing - that is, when I point out the error, they almost always accuse me of not having an "open mind" and I sometimes get a lecture from them about "paradigm shifts" or Einstein or Tesla and so on. etc. Then sometimes they proceed to harass me for months with minor variations of their idea. I always wonder why, if I don't have an "open mind" and am part of the entrenched establishment, why do they work so hard to try to get my endorsement!
Some of these have been pretty interesting ideas that have taken up to a week to study. Some of have been utter nonsense. I was even approached once by someone who claimed to have found some "particles" left behind by aliens who had abducted him, and he wanted me to "analyze" them. Well, I did an analysis and identified it to be a chuncks of Hartz hamster food. But that's another story.
I can't say whether the antenna inventor in this case might have approached someone in the physics department about this antenna, and if he did whether he was turned away, and if so, why.
Just suggesting that (1) we should not condemn the idea outright until we get some first-hand information on what the guy actually claimed - press releases don't necessary mean anything, and (2) if it's nonsense, it is not necessarily reflective of the University's research quality.
An even easier way to tell is look where it's installed and how many towers there are.
"AM" radio (actually, MF broadcast) transmitter sites are almost exclusively found in low, wet, marshy land in order to maximize their groundwave coverage and to get a good counterpoise (RF ground).
Not just that, but many "AM" transmitter sites -- though certainly not all, however -- encompass a number of similar towers in an array, not just one or two. This is done in order to direct their signals in certain directions and to null out their signals in other directions (since MW broadcast signals carry over somewhat great distances after dark).
VHF Broadcast ("FM") and television trnasmitters, on the other hand, are located on high towers on the highest ground available. VHF and UHF are line of sight, hence the higher the better.
As previous posters have stated, "AM" transmitting antennae are the towers themselves. Using the equation 468/f (MHz), a quarter wavelength for 1000 kHz is 468 feet high! VHF antennae, on the other hand, are MUCH shorter and are mounted atop supporting towers.
Cheers, Peter, W2IRT
Groan. This is not as unique as most would have you think.
First, most PCS phone antennas don't have to be shortened. The wavelength is such that it's not hard to get 1/4 wave across your typical portable phone. It's a mere 4.1 cm.
Just so that most of you understand, a monopole antenna is really half of a folded dipole. It has a wire going up and then it goes back down the pole to a field of radials. It has a characteristic impedance of half what a folded dipole would be --about 150 ohms.
In contrast, a normal quarter wave vertical has a characteristic impedance of about 37 ohms (assuming a very good radial system).
Now, remember the part about heating up the antenna? The reason it happens with very short vertical antennas is because there is a current node right there at the base feedpoint. Even a small amount of resistance will generate heat. As you shorten the antenna the characteristic impedance drops. For anything less than a tenth of a wave long, it can drop to less than an ohm. At that point, ANY antenna resistance, even the normal resistance of copper or silver, becomes very relevant. If someone were to use a superconductor, it might make a very big difference.
So a shortened vertical isn't such a good deal. We use them because sometimes that's all we can afford to install on a mobile system. This is why most hams who operate on longer wavelength bands try to locate the loading coil closer to the middle of the antenna. It gets the loading coil away from the worst of the current node, reducing i^2r losses, and increasing efficiency.
Now, take the monopole: The current node is near the top of a quarter wave monopole, not the bottom. We still need a loading coil, however, so that we can match the impedance to something we'd expect a transmission line to have. If we shorten the monopole, we move the current node. The key is to move the current node away from the loading coil, because loading coils don't radiate well.
Thus, what this designer has done is to distribute the loading coil of a shortened monopole so that he avoids the current node.
There are problems, however. First, you still need an effective radial system. Without one, you simply won't have anything that radiates worth a damn. Second, while coil Q factor is less relevant where it stays away from the current node, it still has to be damned good. Further, the current node at the top needs to have very good surface conductivity.
Finally, no matter what, a shortened vertical antenna will have a shortened bandwidth, proportional to how much the antenna itself is shorter than a regular 1/4 wave. TNSTAAFL.
Don't misunderstand, a short antenna doesn't have to be inefficient. However efficiency is not the same thing as gain. Short antennas can not have much gain. That's a matter of physics and mathematics. And the shorter an efficient antenna gets, the less bandwidth it can cover. Despite the steady parade of publicists, that's the reality. Don't buy any snake oil, folks... This isn't really that novel.
Nearly fifty percent of all graduates come from the bottom half of the class!
The "gain" of an antenna comes purely from directional effects, in a transmitter, which is easier to understand, more of the radiation goes out near the horizontal, where it is useful, the apparent gain in receive mode is identical due to the reciprocity theorem. In any situation involving electromagnetic radiation, such as light, or even pressure waves such as sound, the directional properties are always limited by the dimension of the antenna, loudspeaker, lens, etc, in the case of a verticle monopole you really need height to get lots of low-angle radiation, for the same reason that radio telescopes of high angular resolution have several dishes spread out over a great distance, sometimes hundreds of miles. It is also why a 15 inch PA loudspeaker will give, on axis, maybe 102dB at 1 metre with 1 watt input, while an 8 inch hi-fi speaker may give only about 80dB. even though both are equally well made and have had similar attention to loss mechanisms. Likewise the best searchlights have large-diameter lenses....A human eye is large in comparison to the wavelenght of light, so it can resolve lots of detail, the eye of an insect can distinguish only vague impressions of light or colour. There are lots more examples.
Some years ago, the Crossed Field Antenna, which purported to be even smaller, made similar claims, backed up by real-life tests.... I am sure that Google will find lots of references, so why does every AM broadcast station not use one? Maybe 10 to 20 feet high, not too heavy, no expensive materials, yet do you ever see them? Again, it was correctly resonated, but it did not have the height.
In any case I am sure there will be a very large amount of prior art on this one, a fair proportion of CB antennae for instance use loading coils and helixes in just about every combination imaginable. The current distribution of monopole antennae has been widely studied for many years. I would like to see a picture of the thing, to see what, if anything, is new.
Also, the microwave end of the spectrum has no need of smaller antennae, no mobile phone I have seen in recent years has had an external antenna at all, and you can only make a phone so small.. You have to hold the thing, after all. If it is not entirely self-supporting in air, dielectric losses will be serious.