This is a pair of 8-element quagi's, set up for RHCP. Construction is simple, with no critical tuning elements. It has a 50 Ohm dipole feed. Theory: The "quagi" antenna was designed by Wayne Overbeck, N6NB, amd is a high-gain antenna combining the high-impedance and easy matching characteristics of the quad antenna array and the high gain and ease-of-construction of the classic Yagi-Uda parasitic "beam" array.
This design is optimized for It is a slight departure from the design shown in the reference above. The graphic on the right depicts the pattern in free space.
Common Amateur Radio Antennas
The driven element and the reflector are formed out of 12 gauge wire striped from house wiring, but insulation left on and the directors are made from 10 gauge wire. Using stainless steel bolts, nuts, and washers, directly connect the 50 Ohm coax feed to the driven element. I use crimp-on ring lugs to make a neat connection. Table I: Dimmensions inches El.
The free-space gain is calculated at an impressive That is a lot of performance in an antenna you can hold in one hand! A pair of these will provide circular polarization see the picture above and up to 3 dB more gain, depending on orientation. One also makes a fine portable antenna for AO, easily bringing in that bird full-quieting at the horizon.
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The antenna, which is usually built with little more than hardware store materials, became popular in many parts of the world. The original design was republished in amateur radio publications in countries as diverse as the former Soviet Union and India. Thousands of them have been built over the years. Later work on the larger Quagi designs was done in a city park and on a beach in an attempt to get away from reflections and obstructions that made the task of optimizing the antenna design in a small backyard more difficult.
What originally inspired the development of the Quagi antenna was the need for a low-cost, high-gain antenna for moonbounce communications. Some of the commercial antennas then available fell far short of their advertised gain figures, especially at MHz. On a hunch, the driven element was removed and replaced with a quad-style loop. The forward gain immediately increased from 6. That led to exhaustive efforts to optimize this hybrid antenna, working originally at MHz. After many experiments, it was determined that Yagi-style directors delivered better gain than quad loops when the antenna was extended beyond four or five elements.
But the use of a quad-style driven element and reflector offered several advantages, including good gain, good immunity to noise resulting from static buildup, and extreme ease of construction and impedance matching.
After many designs were tried and rejected, the classic 8-element and element designs were selected for publication. Later additional designs for were developed. Computer modeling has revolutionized the way radio amateurs look at antennas. Armed with one of the powerful software packages that have come along in recent years, it is possible to design more antennas in a day than could be designed in a lifetime on an antenna range.
Consequently, actual field measurement of antennas--using the classic scientific method of experimental research--has gone out of fashion. However, computer modeling has its limitations. It is not always possible to model all of the variables that come into play with real-world antennas.
And the modeling process has pitfalls even for the experts. First, I wanted to demonstrate how foolish it's possible to become when you get carried away with computer modeling.
Powerful software is no substitute for common sense. Second, I wanted to point out how easy it is to draw invalid conclusions when you ignore the limitations of antenna-modeling algorithms. Of that amateur, Lewallen said, " One answer is to measure the antenna's gain against a known reference. Often these sessions, in which antennas are sometimes measured side by side as shown in the photo at left, are conducted by antenna experts using professional quality signal sources and measuring instruments.
But any amateur willing to invest some time can set up an antenna range somewhere and obtain accurate antenna gain measurements with nothing more sophisticated than a low-power transmitter, a receiver and an audio VU meter. Because so few amateurs do actual gain measurements today, it seems worthwhile to summarize what that article said here. The article said that any clear area can be an antenna range.
To conduct comparison tests, two antennas are placed side by side on masts of the same height, using equal length feedlines. Then a VU meter can be used to indicate the difference in received signal strength of the two antennas.
As a precaution, the two antennas are swapped so that antenna 1 goes on the mast and uses the feedline formerly used by antenna 2. Given some care in measurements and a stable path, it is possible to determine the difference in the gain of the two antennas down to a fraction of a decibel.
Once the experimenter has confidence in the integrity of the antenna range, it's quite possible to dispense with the receiver and VU meter and use a signal source plus a field strength meter such as the one shown in the photo at right which also shows an assortment of elements of varying lengths, including one mounted on a meter stick for use in antenna design work.
Also, new antennas can be designed using these antenna range principles. A variety of element length and spacing combinations can be tried until the best results are achieved.
While this is far more tedious than computer modeling, it does produce repeatable, practical real-world results. The Quagi antenna was designed in this fashion in The length of the model has been deliberately shortened to allow it fit on a 24 foot boom.
Performance is substantially higher than that of the original antenna. It now compares favorably with yagis of the same length. This antenna has not been verified by actual construction. Gain and front to back will be as stated below. The only component of the antenna that needs verification is the 50 ohm match. Full consultation will be available to the prototype builder during construction. Contact w5un wt. Antenna Characteristics: 23' 9" 11 Element Gain: Optimum: E Plane: Stacking can be reduced up to 90 percent of optimum and still achieve acceptable stacking gain.
Do not strip the insulation. If you wish to use a metal boom with through the boom insulated elements, please apply the following correction to the directors only. Insulators can be commercial shoulder insulators and keepers or as simple asheat shrink tubing with the element held in place by hot melt glue or epoxy glue. Blog Document Library About me. Optimum stacking is recommended, however. Length Material Reflector 0. The above dimensions may be used for non metallic booms like wood or fiberglass.
The reflector and driven quad elements must remain insulated from the boom. Boom Diameter Correction Add 0.
Homebuilt Quagi for 70cm
Powered by Quick.A Quagi antenna is a variation on the venerable Uda-Yagi, which dates back A Quagi antenna uses the same strategy as a Uda-Yagi, using a refltector, a driven element, and then a number of director elements.
However, a Quagi constructs the reflector and the driven elements as "quads" rather than as linear elements. In a Quagi the first two elements of the antenna are quads, the directors are all simple straight wire elements, as in the traditional Uda-Yagi design.
There is a "Quad" class of antennas. They come in single elements, and as arrays. A Quad antenna is typically a single wire formed into a square. The dimensions of the square are adjusted so that the antennas resonates at the intended frequency of operation.
Note that both the Quad and the Uda-Yagi antennas are resonant antennas. If one tries to use them outside of their design frequency limits, results will be poor at best. During transmission the reflected power from the antenna may well cause radio damage. Here is a close up of the reflector and the driven element:. The most recent edition is the 21st. The first thing to do is to enter the afore mentioned Quagi antenna into the simulator of choice.
And here's the results of a simulation at MHz:. In this graph we are looking down onto the antenna with the directors in the horizontal position. The reflector and driven element quads are to the left. The directors run off to the right. The highest gain is to the right, in the direction of the directors, at Of note in these results is the low front-to-back ratio of 4.
VHF/UHF Beam Antennas
This is a low front-to-back ratio. Many Uda-Yagi, and Quad array designs have front-to-back ratios of up to 25 dBi. This design is losing quite a bit of power out the back of the antenna. One other thing to check is the source impedance:. The previous antenna was copied out of the literature. Using that design as a basis, can we improve the performance? Shown below is the same antenna with some tweaks to crank up the gain, and improve the front-to-back ratio.
The antenna has gone from a ho-hum performer to one with some serious specs. First off the front-to-back ratio now rivals the kind of rejection 25 dB talked about in the literature.
Its front-to-back ratio of Second, the gain of So the antenna now has some serious gain, and a better than average front-to-back ratio, with VSWR bellow 2. Not too shabby.
Could we tweak out the reactance? Could we reduce the side lobes?I got some PVC pipe in a home repair shop. This set me back about 50 euro cents per 2 meter which means about 0. I needed 50 cm of pipe in this antenna 2 times 25 cm. Next to this I used 70cm of speaker wire I had laying around and a few tie raps to strap it all together.
It was all Outside of the 70cm band the SWR got quickly bad but all over the 70cm band it was perfect! With the new Quad it was easy! So in the end I got a great little antenna for almost no money, and also did some nice DIY!
Also remember to keep the feed point to the left or right side, not top or bottom, if you want to use for the repeaters. My next project will be either a 2 meter band version of this or a 3 element beam of this 70cm band Quad antenna. By the way, the 2 meter 3 element Quad homebrew version is described here very nicely. Some pictures of my new antenna: Quad 70cm. Dag OM Frans, De quad werkt in principe met elke modulatie en elke modus.
ATV zou volgens mij geen probleem moeten zijn. De antenna is heel snel gemaakt. Als je een wat dikkere draad gebruikt wordt hij trouwens wat breedbandiger. Groet, 73 en veel succes! Necessary cookies are absolutely essential for the website to function properly. This category only includes cookies that ensures basic functionalities and security features of the website.
These cookies do not store any personal information. Any cookies that may not be particularly necessary for the website to function and is used specifically to collect user personal data via analytics, ads, other embedded contents are termed as non-necessary cookies.This low-cost, one- or two-weekend antenna project can help you gear up for satellite communications. It's not unusual to hear relaxed roundtable QSOs between Asia, Europe and North America without the congestion of the HF bands - all made with transmitter outputs of less than 50 watts!
OSCAR 13 is a handy tool that enables you to keep in touch with the gang back home, even when you're an ocean away. This is exactly what I intend to do on a forthcoming trip to Scotland.
Although the commercial antennas I use for OSCAR 13 are not very large, they are certainly not small enough to carry as luggage on a transatlantic flight. The quagi antenna seemed to be the answer to my problem. The quagi is an easy to build, highly effective antenna design developed by Wayne Overbeck, N6NB, that combines the best features of the cubical quad and the linear-element Yagi-Uda beam antenna.
Quagis can be quite portable. If constructed of suitably lightweight stock, a quagi's elements can be removed from the antenna boom and packed in a suitcase for travel.
The boom need not be brought along; another boom - made of wood - can be cut and drilled at your destination. This is not a problem if the signals received from the satellite are always circularly polarized. Although OSCAR 13 transmits and receives using right-hand circular polarization, its signals appear to be circularly polarized only when its high-gain antennas are aimed directly at the sub-satellite point.
This usually occurs at apogee. At other times, OSCAR 13's signals appear to be elliptically polarized and - especially when received on a linearly-polarized antenna - may vary drastically in amplitude as the satellite spins on its axis. This effect, called spin modulation, can seriously reduce signal readability. After experimenting with linearly polarized quagis for satellite communication, I found that spin modulation makes circular polarization highly desirable.
But circular polarization usually involves using bulky, helical beam antennas or crossed Yagis that seem rather difficult to build and adjust. I recalled a QST article by D. Robertson, VK5RN, that outlined a method of feeding a quad driven element to obtain circular polarization. Feeding a quad driven element at adjacent corners presents a unique problem, however: Voltage and current maxima exist simultaneously at all four corners of the loop. Because of this, corner-feeding a circularly polarized loop requires that current be driven into feed points where voltage maxima exist.
VK5RN solved this problem by using a sleeve balun at both feed points. The balun transformers present a very high impedance to the in-phase voltages.