+++++++++++++++++++ See Also Antenna_Rogers-Dobbins_Folded_Conical_Helix-2 ++++++++++++++++++++++ Date: Wed, 6 Mar 2002 20:15:53 -0600 From: "Stuart Rohre" To: , , "QRPp International Membership" , Subject: [121470] The Rogers /Dobbins ARL Folded Conical Helix Antenna paper now published. Revolution in small HF Antenna design! As some of you have heard me hint for about a year, a revolution in small HF Antennas is unfolding at Applied Research Labs, Univ. of Tx. I have been an observer of experiments, sounding board, and kibitzer for antenna design. Excuse my pride and enthusiasm, but my co worker, Dr. Bob Rogers, KM5DR, really has hit on something of interest to antenna location challenged hams. Should we call this the Sun City Antenna? Or we might christen this the "Condo Cone". The publication is in "IEEE Transaction on Antennas and Propagation", Vol. 49, no. 12, December 2001. I have just received my reprint. The title is "Folded Conical Helix Antenna" by Justin Dobbins, and Robert L. Rogers. (I will eventually be testing a HF version of this antenna, on 10 meters.) The antenna takes the conical monopole to a new twist. A funnel shaped structure of PVC pipe or wood, or other insulator ribs, holds a spiral folded dipole like wire arrangement. The initial paper concerns a low VHF model, however, further experiments have shrunk a 10m resonant antenna, based on this principle, to a volume of less than two cubic feet. It can be further reduced in height over the example in the paper, and calculations show that it should be possible to operate on 160m with a patio fitting antenna with 90 per cent efficiency! That was not a misprint, 90 per cent! No loading elements of lumped components, (with attendant losses), are needed. You do have to use a transmatch to move around the band. Materials to make the elements include two differing diameters of wire; even RG 58 has been used for one element that is coiled into the funnel. The folding of the element overcomes the fact that an electrically small cone would have an input resistance much less than 50 ohms at first resonance. Folding raises this back to 50 ohms. The fold is a shorted transmission line. This antenna was produced without dielectric loading. However, that is another method of altering the resonance. Attempts to calculate the SWR and input impedance with NEC 4 did not give consistent results. The design is small in terms of wavelength, and this might be a factor. The folding of the radiators greatly affects these electrically small antennas. At present, each is a one band antenna. However, as to performance, a Radio Shack 10 M rig was used to work FM into the East Coast, (from Austin, TX,) on days of only average propagation with that version. Good signals were obtained both ways. The Antenna has been tested over a 2m X 2m square metal ground plane, as well as in an open field over shallow limestone rock. Increasing the sides of the ground plane did not materially increase the signal. The Antenna IS doing the radiating. The pattern of this antenna is much like that of a vertical (elemental monopole), that is ground mounted. The vertically polarized power level was 22 dB above the horizontally polarized component. The antenna gain is 4.7 dBi, (over isotropic). This publication is available at most College libraries with an Electrical Engineering Dept. I would imagine your local library could obtain it on interlibrary loan. Reprints will be sold by IEEE. Other papers are in preparation, and I have urged Bob to build one for something like 160M, 80M or 40M and maybe other bands, and write it up for QST, QEX, or another ham publication. The big thing about this approach to a small antenna is that it retains a resonant length of radiator, while more efficiently using a confined space. I think this is why the efficiency is so high compared to other "trick" antennas which are little more than radiating tuned circuits or capacity hats. I hope others will be inspired to experiment with this concept. All you need is a ring of insulator material to form the wide part of the cone, (such as cut from large diameter PVC pipe), and some spokes or pipe to go down and in to the narrow part where the feed is placed. Supports for the spiral of folded transmission line have been successfully fabricated from fiberglass strips, or other plastic, or even fish line. The antenna is fitted INSIDE the cone frame, which is an open frame, not closed in at all, thus minimizing materials. Ham ingenuity can be put to the full test with arrangements for various bands. It is conceivable that a smaller cone could be fitted inside a larger, lower band cone, and still have both work. There are many, as yet, unanswered implementations, and this is why Bob said I could let the word out now, to encourage further development in the ham bands. 73, Stuart Rohre K5KVH ++++++++++++++++++++ Date: Thu, 7 Mar 2002 16:10:35 -0600 From: "Stuart Rohre" To: , , , Subject: [121534] Re: [WCARC] The Rogers /Dobbins ARL Folded Conical Helix Antenna paper now published. Revolution in small HF Antenna design! Message-ID: <00f501c1c624$e7db5d40$4e100a0a at rohredt2000> I have had some good questions and I will first refer all to the paper in the IEEE publication. However, to summarize: the efficiency was measured using the accepted method for physically small antennas the H. A. Wheeler , Wheeler cap method. This is a cylinder that fits over the antenna, and you make S parameter measurements with and without the cap. It is a big aluminum can that confines the radiated field, and this reflects back on the S parameters. Electrically small antennas have a kr less than or equal to 1. The resonance by spiraling the wires is reduced 13 per cent lower than the resonance of a solid cone of the same dimensions. This first model was resonant at 111 MHz with 32 MHz bandwidth to the 3 dB points for 2.8 average SWR. Min SWR was 1.3 over the bandwidth. This first model has a ht. of 24.1 cm, diam. over the wide cone opening of 36.8 cm, and r was 30.3 cm, the slant distance down the cone to the narrow end, where it is fed. ( Remember, 2.54 cm is 1 inch, for us metrically challenged types.) There were 16 fold wires and all attached to the wire ring at the top, evenly spaced. 18 ga. was used for all wires save the feed wire which was no. 12. Fold spacing was 6.35 mm. I know this is kind of sketchy, but it starts you off with something to scale. Remember, later models which we built for 10M were smaller, than just scaling from this prototype. The difference between vertical and horizontal patterns was computed by pattern functions in NEC 4. Field strength measurements in an open field test site have confirmed the intense near field and the high current of this design. Thanks for all the interest, other questions should really go to KM5DR, Bob Rogers. 73, Stuart K5KVH +++++++++++++++++ Date: Tue, 12 Mar 2002 18:43:36 -0600 From: "Stuart Rohre" To: Subject: [121958] A Single Band 10M Rogers Dobbins Helical Conical, (Condo Cone) compact HF antenna Message-ID: <042601c1ca28$1c491a20$4e100a0a at rohredt2000> To save those reading the IEEE paper from burning questions, here are the complete details on a 10M ham antenna using this helical /conical principle: "at the AQRP meeting today, K5FX hit upon the best way to draw the antenna. You draw two circles, a little one inside the larger, represents the small cone end, and the large one the wide end and circumferential wire. The small circle is a PVC one inch tube in the 10M model. There, a coax connector mounts in the end of the tube. The center of coax goes to four no. 12 wires, that are each one conductor of parallel wire lines, ie the four enter the tube, join,and make up to the center of the coax jack. They are spaced 90 degrees from each other around the tube circumference. Also at the small tube, the supports of one inch nylon web straps join around the tube held by radiator hose clamp. Also, the other side of each parallel line, 4 each no. 10 wires, come up and will solder to a ground plane, or radials. The nylon straps carry the balanced lines along at constant spacing wire to wire and (larger space) line to line. NOTE: The parallel line element is edge onto the imaginary cone slant surface! Now, from the small tube draw out a parallel wire transmission line, describing a spiral. It is like half a folded dipole element. Where its ends "fold", it terminates on the large diameter ring, with both sides shorted to that ring wire. There are four complete parallel wire transmission lines in the 10m model. They are evenly spaced around the cone. They are just over a half wave long, each one, at 10M. The computer generated 3 D drawing of the paper, conceived some 2 years ago, was probably done that way before they got the simpler prototypes to work with fewer folded wires. It is really confusing, until you see the 10M model described above. They have 11 models done, some smaller diameter, some longer cone slant distance. Draw it first with one transmission line spiraling around to the big diameter from the smaller, and it should be more clear. Each of the four parallel lines, (transmission lines) have the unequal conductors to do the up conversion of impedance, and they are each half wave long. In the 10m model, each line is 16 and 1/4 feet long. There are 4 and 1/2 turns of each of the four transmission lines spiraling down the cone imaginary surface. However, this results in 34 turn pairs, (34 no. 10, 34 no 12, each no. 12 behind, (interior of the cone surface) to the no. 10. What supports the wires and spaces them are the one inch wide nylon straps. The straps go from one inch pipe to the 16 inch pvc ring. They are just over 13 inches long, and are turned edge on the cone surface, (imaginary surface), and the hole for no. 10 is outboard of the no. 12 wire hole, the spacing is 3/8 inch between wire holes, but the weight of the no. 10 causes the web to fold and the EFFECTIVE spacing is 1/4 inch as the line winds down the cone. The 10m model slant height is 12 inches, the tube in the middle is 16 inches, with about 14 being the height of the winding of the transmission lines (axial height of cone). The central tube sits atop a 3/4 inch pvc cross fitting, which has 3/4 inch spokes for the 16 inch ring, and those spokes glue to the ring inner ring surface. The ring is cut from large PVC pipe. It has quarter inch thick wall. To summarize, you have a cone that is built around a 14 inch height of PVC tube plus PVC cross fitting. The nylon straps holding element wires, have a length of 12 inches from the one inch tube meeting point, down to top edge of a 16 inch ring cut from large pvc pipe. Thus, to lap over the one inch pipe and be held by a hose clamp, and to lap over the side of the 16 inch diameter ring, the strap has to be about 13 inches or so. It is nylon bolted to large ring. In this compact volume structure, are spiraled four complete parallel transmission lines, each just over a half wave long at 10M. They are effectively fed in parallel. Where the folded end of each element meets the large ring, there is a shorting of both conductors to a circumferential ring. The parallel lines are each made of unequal diameter wires, formed of one no. 10, and one no. 12. the no. 10 is stranded, pvc insulated copper wire. The no. 12 is copper enamel wire. OK, what we have managed to do is put half waves into a compact diameter relative to the wavelength, and a compact height. It is a very low visual profile antenna for antenna challenged locations. They are operated over a 6 foot square ground screen or plane, or radials. At this time, elevated operation has not been attempted, but a double cone structure would solve the ground plane issue for elevated mounting, or one could use elevated radials. Hope someone will try one. Obviously, you could scale this one to 12M or 6M, but we have no exact information for other ham bands yet. 10 have been built for non ham frequencies. 72, Stuart K5KVH +++++++++++++++++ Date: Wed, 13 Mar 2002 18:47:35 -0600 From: "Stuart Rohre" To: Subject: [122016] More on the Helical Conical and a clarification: 20M is possible in same volume! Message-ID: <001401c1caf1$d5772950$4e100a0a at rohredt2000> OK, the experiments are progressing and that caused a confusion of two differing band models. Between the time I saw the 10M model working, and the time I measured element lengths, they had made a second model looking identical except as to band. The dimensions for 10M I published should be amended to say the four folded elements are each a QUARTER wave long, not half wave. That makes them 8 and 1/8 feet each. There was another model also not labeled that I had found, made of identical slant height, and cone angles, and overall height, and wire gauge, but instead of 10M, it is resonant around 15 MHz. (With slightly longer elements, and taller cone, it will be on 20M.) Make the folded lines longer than quarter wave to start, as there is not yet an exact formula I am allowed to quote to get the thing to resonate without line trimming. Bob has suggested starting with ONE folded element, and make it 30 per cent long. Then, you can trim it, and add 3 others of that optimized length. Another major finding, just since I posted originally, is that with the maximum field at the open end of the cone, the material for the ring supporting the wide end does affect the efficiency thru dielectric constant, and capacitance. Instead of the 16 inch diameter pipe, you might want to find fiberglass non copper coated board material, and make two triangles at right angles to support your wires. This does away with nylon strap, nylon screws, one inch pvc pipe, and 3/4 in. cross, pipe caps, and 3/4 inch pipe. You slot the fiberglass triangles to lock to each other. Epoxy that joint for strength. Simpler construction, as you can drill the slant edge for the holes for the no. 10 conductor, and inboard of those, the no. 12 enameled copper conductor. Spacing of wires 3/8 in. as before. (Drill those holes before assembly.) The other thing they tried successfully, was to reduce the thickness of the pvc ring at the wide end of cone. This field activity will respond to hand movements at this end of the cone while operating, causing the SWR on 8 MHz model to go from 1.2 :1 to 6 : 1 today, if the hand is moved too close to the open end of cone. This was tested over the 2M square copper ground plane on plywood. (Made that way for portability between various test locations). We were testing out on the driveway and open field, and got that 1.2 SWR. The 8 MHz model is made with ONE folded element. You can do that, and endure lower efficiency, but Bob reports the single line models still get 60 per cent efficiency on 10M, and 50 per cent with this 8MHz version. Slant height for 8MHz was still 14 in., height of the fiberglass triangles was 13 inches, and across a base of the pyramid thus formed, it is 11 1/2 in. This 8 MHz model was made more as a pyramid than cone, showing some flexibility in construction while retaining more efficiency than a small loop. I was not aware of the ability to get useable results with only one folded element, but now have seen it work. This single element might need some impedance matching to work with 50 ohm radios, but it is an easier experimental model to determine if this antenna will work for some restricted space you might need to use. Now, again, I want to emphasize that this antenna is suited for restricted volume and low profile needs. If you have the space and ability to erect full size dipole, loop, etc. DO use the air space you have. But, if you are apartment challenged or condo constricted, this might work for you. -Stuart K5KVH ++++++++++++++++ Date: Thu, 14 Mar 2002 12:40:41 -0500 From: Steven Weber To: qrp-l at lehigh.edu Subject: [122078] Re: More on the Helical Conical and a clarification: 20M is possible in same volume! Thanks for the info on this antenna Stuart. I think it's quite fascinating. Wonder how a hazard cone from the side of the highway would work for the form? ...probably a little lossy...kinda conspicuous on the roof too Actually, I think making a "tee-pee" from 4, 6 or 8 fiberglass rods could do the trick. Could make a stand from some plywood to hold the rods until you wind the wire on the rods. I also wonder how this would work on 80 or 160M, where we could really use a small, effective antenna. 72, Steve, KD1JV "Melt Solder" White Mountains of New Hampshire http://www.qsl.net/kd1jv/ ++++++++++++++++ Date: Thu, 14 Mar 2002 21:01:35 -0600 From: "Stuart Rohre" To: Cc: Subject: [122132] Other cones for the Rogers /Dobbins Folded Conical Helix antennas. (Condo Cone) Steve, I have posted to some individual queries, that the cone size has to be about the same ratio 10M down to 20M then roughly linearly scale to 40M, ie 26 inches high, 24 inch slant height, and 32 inches across for 40M. (remember the 10M one is 13 inch high cone, slant height 12 inches, and large diameter is 16 inches, and smaller diameter is one inch). You can use one inch on all the models small end for convenience of mounting a coax fitting. You actually do not end up with a factor of 4 dimension change from 20M to 80M, as the great increase of cone side area when you double the diameter, means you can fit the four folded elements into less height. Also, at the expense of 50 per cent efficiency rather than high 90 per cent range, you can make cone with only one folded helical element. High efficiency comes with using four 90 degree opposed elements starting at small end of cone where the coax connector is located. Fiber glass strips would work for supporting the cone wires, but maybe you could glue the no. 10 and the no. 12 twin line conductors to opposite sides of a 3/8 thick fiberglass rod, to space and support them ? That would place more mass of fiberglass between the line conductors, might have to ask Bob if that is a loss issue. Thin fiberglass board has been used for the triangle supports which are glued 90 degrees to each other, by slotting to interlock before gluing. We know the 8MHz model works FB with two fiberglass board triangles slotted to fit to each other at 90 degrees, and the twin lines are threaded along the slant edges. Remember the line is edge on the imaginary cone surface, ie no. 10 pvc wire hole is in the support outboard of the no. 12 enamel copper wire hole. (Spaced 3/8 inch). No. 10 goes to ground plane always, (all of the no. 10's). All of the no. 12's are soldered together and into the coax center pin. (well, actually solder three no. 12 to one of the others, and have that one left long enough to reach the pin of the coax jack above the junction). Lest I confuse you, for construction purposes we have talked about the cone as it sits on its wide end. IN USE, it must sit small end down on ground plane, wide end up in air. The wide end has high field levels and is where the radiation is happening, so it must be in the clear. Another thought, some might be inclined to put a "radome" over such an antenna. Well, do not make it of PVC, instead we used a plastic garbage can, and that did not attenuate the signal. Of course, it is large enough to not have too close coupling to the antenna. PVC pipe of 18 inches diameter had too much dielectric capacitance effect. Of course, I guess the neighbors might wonder about an inverted plastic garbage pail on your roof!!! But a solid rubber traffic cone would be too tall re slant height, and too lossy re electric field high intensity near the wide cone end. And the color--- Also, its diameter is too small. Got to stay in that wide, short , range of kr<=1. And toward the lower end for small antennas at 80M and 160M. kr term for those not familiar, is a rating where r is radius of the enclosing sphere of a small antenna. k is the constant. By convention an Antenna is called small if it fits in a sphere of kr<=1.0. Some one asked if they could build the folded lines of TV twin lead. No. The whole point of the folded Conical Helix is to keep the Radiation Resistance high for the size, and that is done by the transformer effect of unequal diameter conductors in the parallel line folded elements. If we get a chance, I will see if Bob will let us photo the test cone on the ground plane at such an angle as to show the construction and see if we can get it posted to the Lab web site. Might have to get sponsor approval, but worth a try. Remember, as in all antenna experimentation, cut the resonant elements longer to start. Bob suggested making one folded element longer than quarter wave formula, and then, by trimming to get it to work at your frequency, before adding 3 others. The quarter wave formula he uses may be the 234 over frequency in MHz, but in all the other things that happened in the field test yesterday that I was observing, I forgot to confirm the formula. Hopefully cutting long will put you into the right length when you trim to lowest VSWR re 50 ohms. Note that with only one folded element, the best VSWR on 8 MHz is 1.5:1. But that is OK , you have to use a transmatch with these anyway to move around the band. +++++++++++++++++++ Date: Thu, 14 Mar 2002 20:43:52 -0700 From: "James R. Duffey" To: , qrp-l Subject: [122142] Re: Other cones for the Rogers /Dobbins Folded Conical Helix antennas. (Condo Cone) Stuart - Thanks for keeping us informed on this new shortened antenna design. I will look up the reference you gave the next time I am at the library. You mentioned feeding the 10 M model against a 6 foot square ground plane. This is a good, but not excellent ground plane for 10 M. Do you have any data on how a regular loaded monopole (with a good high Q loading coil) of the same height fed against this same ground plane would perform with regards to efficiency? This would be useful information to determine if the complexity of this new antenna type is warranted with the respect to the increase in efficiency over traditional loading techniques. I fear that the 10 M model scaled to 40 M accordingly to your prescription will have a very narrow bandwidth if built with low loss conductors. Keep those technical posts coming. - Dr. Megacycle KK6MC/5 -- James R. Duffey KK6MC/5 Cedar Crest, NM DM65 ++++++++++++++++ Date: Fri, 15 Mar 2002 20:36:19 -0600 From: "Stuart Rohre" To: , Subject: [122203] Another word description on the Rogers' Folded Conical Helical Antenna Apparently some hams have not seen an all metal conical antenna, or Bi Conical, (two cones), and thus are still having visualization issues with this experimental antenna design. Also, I realize it might be easier for most, and those visually impaired, to first hear of one made of ONE Folded half element. The radiating structures here, are half of a folded dipole. If you cut BOTH center wires of a folded dipole, what is left is the HALF of the folded dipole that gets fed by a coax on this antenna. The half element, is wrapped around spiral wise on a sloping surface to form a cone. There is no solid surface, just the apparent surface of the wires making up the parallel line. The parallel line sits with the plane of its wires horizontal as they wind around making the cone. The twin line is NOT flat to the slant height. The challenge, when you build a four folded element model, is on the element supports for the wires, you have to wind the first element in the first pair of wire holes, then skip 3 pairs, and the next turn at that element support for the first wire pair, is down the cone below the skipped 3 pairs of holes. Thus, when you wind the second element it is next to the first turn of the first element, and so on. The third element is below the second, and the fourth element next. The elements will end up evenly spaced around the wide end of the cone if you do things correctly. Making a model of cardboard and string is the way to work this out to your satisfaction, before making the electrical model. So below, is another description, with more alternate materials suggested for element supports. Good Luck, and let me know if you get stuck, 72, Stuart K5KVH Have you ever seen/felt a sloping ground plane on those VHF antennas from Radio Shack? That is a conical structure made of straight radial elements hanging in parallel around a conical slope. But, this Rogers' antenna has horizontal wires making up the cone by making them spiral around and down the length of the cone slant, called the slant height. That is the 12 inch dimension. Those wires are actually parallel transmission line, put on in the special way I will describe below. Let me see if I can describe some tactile model for you. Please send further questions until you get the concept. I have suggested to many, to build a cardboard model first, to work out your understanding of the conical concept, especially if you do the four element model. But, a one element model is the best first one to do, to see it work. A cone, as you may know is a sloping pointed object, rising from a circular base. Instead of a narrow point, the cone for this antenna forms an open outlet, (like a funnel has) It is for mounting a coax connector, as the cone antenna is used wide end up, narrow end down over a ground plane. The ground plane is best if 2 m square (about 6 feet on side) of copper screen. But it is easier to describe the cone formation as you build it,-- with wide end down. Now, the cone surface is imaginary. That is, you have to have a cone shape for what you do with the antenna elements. But there is no material except some wire insulators at the cone edge. We have improved the wires support now. An easier way to mount the wires than the first model using PVC pipes and nylon tape, is to have plastic or fiberglass triangles. or shellacked plywood, at right angles to make the outline of a pyramid. Narrow end up, wide base down while building. The wide base will become the large diameter of the cone. I would try 1/4 inch plywood, or circuit board thickness fiberglass sheet if you have that. Plexiglas would work, but would be expensive. Along the sloping sides of the triangles, (four sides), you drill holes for holding the wires. The outer hole of a pair, is for no. 10 pvc insulated copper wire, then 3/8 inch inside toward the center of the triangle, you drill a matching hole for no. 12 copper enamel wire. All along the slant height, you will drill pairs of holes like this. The pair is horizontal. If you build a model of cardboard triangles and string you can visualize, or feel this ant. form. The two wires form a parallel folded line element, but you can think of them as TV twin lead with one wire larger than the other wire. The spacing between pairs of holes and wires is 3/8 inch horizontally. The triangles are slotted to slip into each other, and glue together at right angles. Then, start at the narrow, top, pointed end,and wind a no. 12 wire down to base wide part. It has to go thru a hole in each edge of the triangles for four sets of holes. It will wind down as a spiral, one turn below, but spaced, from the one above. Leave a pigtail at narrow top end, for center of coax connector connection. (I am first describing a one folded element antenna for ease of your understanding, and you can use it as well, as it is better than 50 per cent efficient, while small loops like MFJ are only 10 per cent.) Now, outside of the no. 12 wire you wound, which was a quarter wave long, (if 10M band, that is 8 1/8 feet of wire), you wind the larger no. 10 wire. It also is left with a pigtail at top for ground plane connection, and is also 8 1/8 feet long,and winds evenly spiraling down to wide base of cone. It will be side by side with each turn of the no. 12, that ends up inside the no. 10 wire spiral. That is joined at the wide bottom end, to the no. 12 wire, as a folded dipole half element is shorted at its end. Now, you have made a one folded element helix antenna. If you made 3 other folded elements, and had enough holes on the edges of the triangles, you could wind them down at 90 degrees to the start of the first one and each other. (As you look down on the cone is when you would see each folded line starts 90 degrees around from the first). This four folded element model is the most efficient, but to get you started, make one with one element to get the idea. Now, to make a four element model, you have to realize that you start the first folded element in the first two holes of the narrow top of the triangle edge. But, you have to leave the next three pairs of holes empty, before bringing the next turn of the first folded dipole half element around as the second turn. That is because you will be winding the first element in first two holes, the second element in second two holes, and third hole in third pair of holes,and the fourth element in the next pair of holes. Then the sequence starts again with another turn of the first folded element. If you make the one folded element model, have the one quarter wave line spiral 360 degrees around the cone evenly in the 12 inch slant height. Remember the cone is made 13 inches high, plus your coax connector. The base diameter of the wide base should be 16 inches. The four element model fits much more tightly wound in the same 12 inch slant height. You just drill more holes. If you were to look down from the top of a cone, Ie standing over one, there is a little circle which is the top end of the cone. (like a funnel), and the larger circle is the outside of the wide part of the funnel. Does that concept help? Of course, your winding twin lead made of the two unequal size wires, edge on the cone is what makes the cone "surface". You must provide some support for the two wires that make up two wire cones. Some have suggested using fiberglass rods for wire supports. Maybe those could be notched,and the wire hot glued to them. I imagine for a first model, plywood triangles that are shellacked would be useable, but I would keep power down to 25 or 50 watts until you determine that nothing is heating up. There is very high electric field at the wide part of the cone, which is upmost in use, and over the ground copper screen plane. You mount the coax connector to your screen and the coax goes below the screen, using a right angle coax connector, or straight down if you elevate the ground plane above physical earth. Hope this helps some more, Stuart K5KVH ++++++++++++++++++ Date: Fri, 15 Mar 2002 21:20:07 -0600 From: "Stuart Rohre" To: "James R. Duffey" Cc: Subject: [122207] Cone comparisons to loaded monopole Jim, Well there are loaded short monopoles and there are short loaded monopoles. :-) The figure of merit for short antennas in this kr<= 1.0 class is to measure the efficiency of radiation by the Wheeler cap. IE, you short out the field by covering the antenna with a conducting cylinder with one end closed, open end toward and shorting to the ground plane under the test article. You make s parameter measurements of the capped antenna and again with it in open site. The efficiency calculation that comes out of that shows in excess of 90 per cent over the 3:1 VSWR bandwidth for the 10M model folded conical helix ONLY 13 inches high. The ground plane size was picked as typical of some ocean buoys and is electrically large compared to the smallest buoy ground plane area for HF. For some similar short, but folded monopoles much shorter than quarter wave, the efficiency is only 10 per cent or less. Of course, the longer the loaded element, the more efficient it gets. The coil losses are another factor. Some ham stick type antennas are much inferior to others in size of wire in the coil. However, there are places where a tall slender loaded whip cannot be used. What if you had a buoy that would tip over if you had a whip antenna on it? With ocean winds and waves, wash over is a concern, and the folded conical helix can be put into a radome to protect it more easily than taller antennas. Not all ham considerations, unless he has a boat, but this was developed first as a seaborne antenna. My thought is that it is good CC&R work around for apartment hams. What if you have an 8 foot ceiling on the balcony of an apartment house with antenna restrictions, and only a non antenna appearing sculpture on your balcony could be used as your antenna? A little low profile antenna might allow home ham operation. There are plenty of height restricted applications for the ham. One of these cones up on the roof of a van for 10M would work a lot better than a bumper mounted short loaded whip, or helical monopole. On one van we measured, the best VSWR for bumper mount helical monopole (Ham Stick) was 2:1 rapidly rising to 3:1 over the band, or worse. It had very poor performance in some directions. I think the Outbacker type antennas have been measured at very low efficiencies. I have one for demo purposes, but it is never a star performer. It is a even large for some small cars, (mine). If you use the two triangle sheets of fiberglass that we now are proposing, the complexity of the helix is lessened. The parallel lines are spiral wound most easily, and if one is only wanting "to see it work", in the same size cone, you can construct the one parallel line model, of same materials, and get over 60 per cent efficiency. The triangles could be bored out, for less wind loading. Even shellacked 1/4 inch plywood supports for the wires would work at QRP and maybe 100 watts, as would masonite and maybe even heavy cardboard shellacked to make it water resistant. What most have not realized with the four folded elements model for 10M and even for 20M in same size there will be full wavelength of wire in only 13 inch height and fitting in a 16 inch diameter. That is attic sized for many places, if you have a place that is about twice that volume, clear of wires and conductors. We expect to have to use a transmatch for 40M, we advocate it at 10M. Of course as with any antenna, there is no free lunch, no way to cover all a band with no tuning, when you shrink the thing this much. +++++++++++++++++ Date: Sat, 16 Mar 2002 07:54:21 -0700 From: "James R. Duffey" To: Stuart Rohre Cc: Subject: [122227] Re: Cone comparisons to loaded monopole Stuart - Thanks for the reply. I am sorry if you misunderstood my intentions. It was not my intent to crticize the new antenna or imply that the data was bogus. The point of my post was to see how the performance compared to other short loaded antennas. That is why I asked about the efficiency measurements. I am aware of the Wheeler Cap method of measuring efficiencies and its widespread use in the short antena community. It is a good solid time tested technique. I am also aware of the low calculated efficiencies of short antennas. I just would have liked to see a measurements of the new antenna compared to measurements of a more conventional short loaded antenna. This would have helped to ascertain if the complexity of the new antenna is worth the additional efficiency. That is, what I was seeking was an apples to apples comparision, not a measured to estimated comparision. When new technology is introduced it is always nice to measure the claims of improvement against conventional technology to see how much is actually being gained. That is why I asked about comparable measurements over a short loaded monopole. Now I realize that doesn't adequately describe the antenna I would like it compared to, but lets say for comparision sakes; a rather thick monopole (2 inches or more) of the same height as the new antenna, loaded at the top with a disc the same diameter as the new antenna, perhaps augmented by a high quality inductor (say Q > 200 or more) connecting the disk to the monopole to provide additional loading, and fed over the same ground. Getting away from monopoles, there are other loaded structures using the same impedance transformng method of varying diameter conductors that might be usefule to comapre it to. Do you have a good idea of what the ground resistance of the 6 foot square ground plane being used at 10 M is? -- James R. Duffey KK6MC/5 Cedar Crest, NM DM65 ++++++++++++++++++ Date: Mon, 18 Mar 2002 19:38:09 -0600 From: "Stuart Rohre" To: Subject: [122477] Fw: Cone comparisons to loaded monopole Message-ID: <005901c1cee6$b995d990$4e100a0a at rohredt2000> Here is some info on papers by a group that wrote on short monopoles and on conical antenna. However, they were working at higher bands than the Rogers/Dobbins work. Bob is going to get me copies of the two papers listed below. Subject: Re: Cone comparisons to loaded monopole. Bob is testing outdoors in comparison to one of the loaded whips that offers a slim coil distributed along the lower 1/3 of antenna with a whip above. Personally, I am going to urge they also do other comparisons, such as disk loaded monopole that was in QEX awhile back. Bob is predicting that he can do 160M with acceptable efficiency in 8 feet height. > Hi Jim, > No, I did not take your comment as criticism. I will pass on your good > suggestion on the comparative measurements to Bob Rogers. I am printing out > a bunch of messages of comments from various good folks. Of course, we are > tasked to come up with an alternative to the thick disk loaded monopole > because of its c.g. (center of gravity), in the sponsor's application > > The sponsor has this buoy requirement, that just cannot tolerate a longer > antenna nor have it suffer washover. If it was in a radome, that upsets the > balance of this buoy, as it is not a big one. Interest is in air launched > buoys now. What might be of use to hams is comparison of the single folded > element model to the four folded element model. Actually, once you have the > supports drilled,both models are simple to assemble. One just takes more > holes drilled in support arms. And the added material. But, with the main > material being four quarter wave wires of each size, that is not too much > for most folks to come up with. I have some folks looking at alternate > insulator materials, that any home center could furnish a ham. > > > The detail of the 6 foot square plane, is household square cell copper > screen tacked to hinged sections of plywood for convenience in folding it up > to take to field site. Jumpers across the hinges ensure integrity of the > ground when deployed. > > I will try to get a resistance per square unit figure for you sometime this > week. (I am on another project that limits my kibitz sessions at the > antenna test site to coffee breaks.) However, that is most fun a ham can > have, is playing with something like this antenna. > > I know Bob consulted with the team of H. D. Foltz, J. S. McLean, and G. > Crook, who authored "Disk Loaded Monopoles with Parallel Strip Elements" as > well as "Singly and Multipally Folded Broadband Conical Antennas". > > Their monopole paper was in "IEEE Trans. Antennas and Propagation", Vol. 46. > pp 1894-1896, Dec. 1998. > > The Conical paper was in "USNC/URSI National Radio Sci. Meeting Dig., > Atlanta, GA. 1998", pg 262. Now I bet that meeting was hosted by Ga. Tech, > so that might be a source of the Digest. > > I would expect consulting those two papers answers the loaded Monopole > vs.Conical Helix questions. I am hoping to get those myself from Bob, or > the authors. > > One of the things I hope to try is a 10M model over say 16 radials, just to > see if that puts out similar field strength to the lab test model over > plane. Of course, it won't be as good, but how close is of interest. > Radials of 1/8 to 1/4 wavelength would be of interest to me. > > 73, > Stuart K5KVH +++++++++++++++++ Date: Wed, 3 Apr 2002 22:29:45 -0600 From: "Stuart Rohre" To: Subject: [123936] A vertical dipole over water, or with lower element insulated but under surface of water gang, As more experimentation is being done on the Buoy that is going to try the Folded, Conical Helical antenna later this month, we also are investigating other options. Initial testing with a quarter wave or loaded whip, (lower part a fiberglass helical coil), showed disappointingly high SWR,and bad impedance match to 50 ohm RG 58 of about 2 feet feeding the transceiver. (Ft 817 modified). And that was in air, about 3 feet above our limestone back lot. I suggested we explore making the antenna a half wave vertical dipole, as the buoy is about two feet in diameter, and has a hollow core for wires to go down to the batteries in the bottom of this spar buoy. I suggested we sleeve the wires with braid as the lower element of a half wave,and see what the effect of half of the dipole being dry, but below the surface of the ocean might be. Now, we do not have the lab on the ocean, but we do have our own test tank out back, a little old swimming hole with a redwood wine tank in it 60 feet in diameter and 40 feet deep. We figured that any conductive effect of fresh water in the tank would only be magnified by sea water. Well, Lew W5IFQ, hoisted the spar buoy up on the crane over the tank, and carefully measured the vertical dipole in out of the water, (but inside the buoy for the half element length). Feed point was at top of buoy. We also made a half wave line coming off at right angles to allow the antenna analyzer to inspect the feedpoint Z. Looked good, and low SWR up in the air, supporting the buoy with non conducting straps off the crane hook way up 5 stories above us.. Then we floated the buoy. Uh Oh! SWR with buoy antenna half, mostly below water surface but inside dry buoy, was 12:1! Z was way off. The resonant frequency that we had cut by formula in air, was also shifted. The buoy floats with feedpoint about 18 inches out of the water. A diver helper, pushed the buoy top down to almost enter the water,and this would shift the resonance as you would expect. The water column outside the pvc buoy case is acting as an RF choke, for all intents and purposes. This was at 30 MHz. Then, Lew got some ground braid. He let it touch the chassis of the transceiver cage, and drape over the side of the PVC buoy pipe into the water tank. SWR came down with two straps, and Z was back where it should be. We will use two stainless steel straps to contact the salt water down at the beach. Have to have something rugged as launching a buoy off work boat causes it to bang up against the hull, and you can't have horizontal radials and do that. I have suggested a plan two, that would take a couple of Steel measuring tapes and make flexible radials out of them for elevated radials, or gull wing radials. (See Force 12 Antennas web site, for explanation of gull wing radials in the K5K operation.) Likely, they would be loaded radials, as the tapes would not self support at full length of a quarter wave. The case for the Folded Conical Helical is getting stronger, as it would sit on top of the buoy with only the low profile of the 13 inch high model, or possible the newest, which is only 6 inches high. We would still use the stainless steel straps to water, and make them radials. I also have plan three, which is an inverted inverted vee helical loaded dipole, or Vee dipole. The Vee might be able to work on this rather tall buoy, as it is balanced to hang vertical in the water column. Washover, though was a concern, that the fiberglass coated helicals "might" solve. We likely will kludge up a test version of that out of water first, and see what the field from such close spaced dipole elements might be. Lew said he would model it too. He is taking L. B. Cebik's new modeling course interactively thru ARRL. Some of the issues here are we have some computer stuff that has to work in this RF field. RF in the shack as it were! 72, Stuart K5KVH ++++++++++++++++++++ Date: Fri, 5 Apr 2002 18:18:39 -0600 From: "Stuart Rohre" To: Subject: [124054] Flash: Folded Conical Helical Antenna made for 15 MHz only 6 inches tall! Message-ID: <006b01c1dd00$99c99cf0$4e100a0a at rohredt2000> Folks, It looks pretty good. A smallest to date, Rogers Antenna of the Folded Conical Helical design for 15 MHz has been tested by the Wheeler Cap method and is 60 per cent efficient. It is composed of a cone of two parallel Folded Conical Helical Monopoles wound as cones in a 6 inch height. Naturally, if you can use the taller models having four monopoles in parallel, you are better off and can get over 90 per cent efficiency by the Wheeler Cap test from them, using 13 inch height. I guess the upcoming trip will have one of the smallest ones for higher band tested against a commercial loaded helix with top whip, using the stainless steel salt water radials to effectively ground to sea water. 72, Stuart K5KVH +++++++++++++++++ Date: Wed, 10 Apr 2002 15:50:02 -0500 From: "Stuart Rohre" To: "JOSE VICENTE" Cc: Subject: [124339] Re: Folded Conical Helical Antenna, more instruction steps for the 10m model in 12 inch slant height cone shape. Message-ID: <000401c1e0d1$49aa0370$4e100a0a at rohredt2000> Joe Vicente asked such good questions, I wanted to share this with the group: Joe, for 10m on 16 inch diameter model: The elements made up of the parallel wires are each made longer than a QUARTER wave to fit the 13 inch high cone shape winding down the 12 inch slanted side, which links the narrow top to the 16 inch diameter wider part. Start with two wires 8 1/2 feet each for each monopole, and see what that does re resonance. If not long enough you have to use longer ones. IF too low in band, cut 1/4 inch shorter and see how much that moves it. Cut equal amounts from both wires. If you were to place the supports for the wire on a table with the 16 inch side down, and you looked down on the structure from above, you simply start each monopole element, (two wire pair) at a compass position, ie, one pair of wires (one no. 10, one no. 12) starts at the North position if it were a compass rose. Straddle the North point with 3/16 inch space to the 10 wire, and 3/16 inch to the 12 wire for total wire to wire space of 3/8 inch. The next is at East, next at South, and finally one at West. If you made the sharp end of the cone for type N or hardline coax connection, then you probably end up with less than an inch from each start of a pair. Maybe less for type UHF, it is not critical. All the two wire pairs have to come together at what would be the small point end of a conical support, in order to join all no. 10 to the outside of the coax connector, and all no. 12 to the center tip of the coax jack. Remember, when in use, this small end goes closest to ground plane screen, or radials. The large diameter end, has the fold of each wire pair made to fit to the very edge of the 16 inch diameter. But, before you affix the final positioning of each wire, you have to trial fit them to the conical shape, as no simple geometric formula yet exists to position each. Remember the 16 inch diameter end is UP in use, in the air over the ground plane. One ham solved this fitting question by using pins into wood supports to trial fit his wire. You need to trial fit the longer than QUARTER wave monopole, and check its resonance. If it is close enough to the part of the band you need for lowest SWR, then OK, if too low in frequency, cut some off the end, and reshort the pair, (no. 10 to its corresponding no. 12). When you have the monopole element within the band where you want it, then do final fitting of the spiral to the supports. using holes to thread the wire thru supports is one way of holding their position, by drilling side by side no. 10 hole, and no. 12 hole, When you first trial fit the pair to the cone selected, you will determine how many turns fit your slant height, then make the holes for say four monopoles, or if using only one or two, the holes for turns, of course, spread out along the slant. The spacing in other words, should be even along the 12 inch slant; whether you are building a two monopole or a four monopole version. The spacing of course, is closer together for the four monopole version. You may have to move things around to take into the account the thickness of insulation on the individual wires. They end up quite closely spaced in most of our trial models. We have even made one to test that does not form a cone, but uses two triangle supports of fiberglass and straight runs of wires between the slant sides, to form a square pyramid. We are testing this this week, but do not suggest it at this time, until our Wheeler Cap results show it is still efficient. A Cone uses up wire the best. Remember the four monopole model which is most efficient; has a more gentle slope to get more wires onto the slant than the two or one monopole models. I suggested to many, to start with the single monopole to get a feel for the building procedure, then add the other one monopole or the other three, which is the best you can fit in such small volume for 10m. on the size form we used: 13 inch axis height, 12 inch slant, 16 inch cone diameter. 13 inch height does not count the coax connector you choose. You must use a ground plane or radials or your SWR will be high. We just built a 6 inch high, 10m band one, also with quarter wave monopoles; but could only get two monopoles wound in such small height. I will have to measure the diameter, but I think it was 8 inches, ie you always scale this design from a size that has been lab tested, in even amounts, ie half size, or such. For 40m or 80m you would have to multiply larger, (scale up) and the cone might be 26 inches high, or 52 inches for 80m, for example. Are you using pvc insulated wire for both? But really, this is an experimenter's antenna, you should expect to trial fit with even spacing, even with a couple of tries being needed to get it spaced evenly. If you are using something other than wood for supports; some have suggested using tape to temporarily establish the position of a pair on the support to get a feel for winding layout. Masking tape is easy to remove after you get spacing marked. As long as you evenly cover the surface area available on a given size cone, yours will work well. Remember, that since the plane of the pairs is constantly changed by the winding of spiral like turns on a screw, then each always has an opening to space to radiate, and will not be blocked by the other turns, if all are equal spaced. The wire to wire spacing however, (with no. 10 and no. 12) is set at 3/8 inch to give the right impedance transformation with four monopoles (to 50 ohm feed). If your spacing is not kept uniform wire pair to wire pair, your result might not be as good. Keep pairs symmetrical to other pairs, keep each pair spaced uniformly at 3/8 inch all the way to shorted (fold ) end. Your last question on spacing for four monopoles, can be answered best by saying when winding one or four monopoles around this slanted surface, you really end up with two cones of wire. The outer cone is the no. 10 wire for one monopole, or wires for more monopoles than one. The inner cone is the no. 12 wire, and the other no. 12 wires of other monopoles, if used. Remember, you wind turn one, a pair made up of 10 outside, and inside, and beside it, no. 12. Then, before you go to second turn of first monopole pair, you start the second monopole pair, and after its first turn, you go back and start 90 degrees spaced at end, the third monopole pair, and then next is the fourth monopole pair. Did you look at the drawing of original paper? Please just use some typing white out ink and eliminate the multiple pairs there, until you have only four monopole pairs, and it should be more clear. Perhaps I should also say, at the 16 inch diameter end, you could start THERE, and mark four positions around the circumference, and you could start at North with fold of folded monopole #1, and at East with #2, and South with #3, and then West with #4, and wind up to the small end, the same way, making one complete turn of first pair, then laying next the first turn of second pair, and next the first turn of third pair, and finally the first turn of the fourth pair. Now what comes next? The SECOND turn of first pair, the second turn of second pair, the second turn of third pair, and the second turn of fourth pair, and continue on in this manner. Somewhere in one of my early posts to the list I listed the monopole turns count for 10m model, I want to say it is about four (5?) turns of each monopole, but again this can vary with your choice of insulation thickness on the wires, and is not important. What counts is covering the surface evenly with pair turns, small end of cone to 16 inch diameter end. Whether you go clock wise or anti clockwise is of no concern, as this is a linear polarized antenna, the radiation is from the long dimension of the wire, ie not circular axially like the VHF conical helix. You could start at wide end, and wind all monopoles up until the open end of the wires will reach the coax connector. Which ever is easiest to visualize for you. Maybe the BEST way to start is at large end, and there of course, 16in. diameter is Circumference equals Pi (3.14) times the 16 inches, or about 48 inches circumference. Divide that by four monopoles, and each fold should start its monopole winding 12 inches around the circle from the next monopole. Mark the start positions and center the monopole pair there, and start winding up the slant. Remember the objective is to end up with the resonant length filling the conical surface by corkscrew turning around the supports. The purpose of the antenna is to have quarter wave resonance of four monopoles in parallel to a coax connection, but spread over a small volume which is made up of this spiral surface, we have, for convenience, called a cone. It is the individual wires that make the cone surfaces, one outer and one inner cone. The spacing, monopole edge to monopole edge, on our first 10m model (because the no. 10 had thick plastic, and the 12 had enamel coating), was more spread out pair to pair than one made of two plastic coated wires. But, center to center of a wire pair should still be 3/8 inch for the 50 ohm transformation. That transformer action is dictated by the choice of unequal wire pairs sizes, (no. 10 and no. 12) and the spacing by parallel transmission line equation. However, once we have this inequality, we have enabled the line to radiate as an antenna element, known as the quarter wave monopole. We have laid the rather tall quarter wave element on a slant to fit the small cone area. You can vary quite a bit in the spacing wire to wire as the winding is done, (as a practical matter), and it will still work. However, overall efficiency is dependent on even spacing and uniform winding. I am sorry at this early stage that we have so little detailed instructions, but we are finding out these things day to day. We have gone thru two winding equations, and still do not have a simple way to find the hole positions, but hope to bring some uniform information from all the hams experimenting with these. You are one of at least five or six who are already working on this idea, so you are a pioneer, and I may learn (for Bob Rogers) things from your model that might help us define this design into a standard. Remember, Marconi and Hertz started just like this to develop the dipole, and loop and flat top antennas, and had to cut and try at first. Good Luck, and Please keep me informed and ask further questions as you think of them. Remember to use a transmatch if your first winding with four does not come out resonant inside the ham band. It should be possible to cut one monopole to resonant band point, and make the other three the same length. Work at getting it in the band, then apply a transmatch to move lowest SWR point around. However, it may be you could stagger tune them for broader low SWR??? That is just a guess from other antenna principles. The size of 12 inch high cone should be OK to 100 watts with the wire specified, but we have not yet had an amplifier to try more, (we will), so if you feel brave and have more power let us know what happens. There is INTENSE field at the 16 inch diameter portion, so test well away from conductors and outdoors if possible. It really is intended as an outdoor, or patio antenna, and we do not know what it would do yet, in an attic for example. Please, to be uniform in reports, do your first testing outdoors, above the specified 6 foot square copper window screen ground plane, or equivalent radials I feel 16 radials would be a good number for now. Thanks for your interest,and let us know how your prototype works. 72, Stuart K5KVH ++++++++++++++++++