You need an environment free from long lengths of metal. The ocf short vertical dipole for hf has become popular, particularly disguised as a flag pole for low impact installations and encouraged by claims of outstanding performance. Construct a multiband offcenterfed ocf dipole covering the 40, 20, 15, and 10 meters amateur radio bands, and possibly the 6 meter band but that is considered a bonus band, outside the main project objective. Antenna book, basic antennas compendium and classics series rsgb publications practical wire antennas and hf antennas for all locations cq communications sevicks and maxwells books on xmsn lines, baluns vertical handbook, all about quads 20.
The quality workmanship is far superior than others. A transmitting antenna transforms electric currents into radio waves and a receiving antenna transforms an electromagnetic field back into electric current. A dipole that long ocf or otherwise, doesnt matter will have a lot of lobes on the higher bands, and they will favor the ends of the antenna rather than broadsides. The original was for 160 meters and i cannot say a bad word about the antenna. Heavy duty stainless 14 inch center threaded, cemented with lock nut eyebolt supports. The theory of the antenna length is to make the antenna nonresonant on any amateur band so that the impedance at the. Just what is a dipole antenna, and why are they so popular. Feeding the ocf dipole at a point that is onethird of its. An antenna is a device that provides a transition between electric currents on a conductor and electromagnetic waves in space. Homemade carolina windom antenna m0ukd amateur radio. The picture above on the left shows the classical dipole, which is usually fed with 50 ohm coax, through a 1. The centerloaded offcenterfed dipole clocfd was invented and first described by yours truly, serge y. Further research indicates that the total length might need to be. A photograph of a typical corner reflector is shown in figure.
Off center fed ocf dipole antennas ham radio site home. Resources listed under ocf antenna category belongs to antennas main collection, and. A choke balun between the transformer and the feeder prevents this. Bus healy, nj2l assistant technical editor ipole antennas have been widely used since the early days of radio. A commercial antenna system, the buckmaster 7band ocf dipole, exploits this property.
The 4band fritzel model fd4 is a special version of a windom antenna. Ohms, the theory goes that we should be able to find any impedance between these two extremes along the antenna. Ocf antennas are very convenient as they will allow multiple bands of operation with a simple wire antenna which is fed off center with a 4. The short end was placed at about 40 feet off the ground, tied to a tree limb, using about 10 feet of insulated rope. Describe your experience with the buckmaster 7 band, 300w, ocf dipole antenna and tell us why you give it the rating you did required. Whats the difference between these two ocf designs. Wanting to discuss ocfds and singlewirefed windom antennas. Other useful information would include your experience with similar products, infomation on a product that you would purchase instead of this one, and so on. This antenna has moderately high gain, but its most important pattern feature is that the. The higher the frequency the closer the feedpoint must be to the center of the current maxima on that band.
Radiation is the term used to represent the emission or reception of wave front at the antenna, specifying its strength. Last year on field day i was able to use an ocf dipole for the first time, and i enjoyed the quick bandswitching it allowed, so i thought id try and find a good ocf dipole for use while in the field. The part of the antenna nearest to the feeder radiates most and operates like an invertedl with the outer of the coax. Antenna here is a dipole youve probably heard this phrase in many qsos. Submitted to the faculty of the worcester polytechnic institute. In depth antenna theory can become quite complicated, but a qualitative and simplified theoretical explanation help help in understanding what is actually happening, how the radio antennas work, and how they can be optimised.
In this chapter we shall explain the basic concepts of antenna theory from the engineering point of view which will be helpful in understanding the radio telescopes. The ocf dipole presents a reasonably good match to the transmitter across multiple bands which are even harmonics of the fundamental frequency, including 80, 40, 20, 10 and 6 m bands. Antenna book, basic antennas compendium and classics series rsgb publications practical wire antennas and hf antennas for all locations cq communications sevicks and maxwells books on xmsn lines, baluns. On 40m that antenna will have six lobes, four skewed about 45 degrees off broadside in two directions, and two more broadside that are somewhat smaller directly broadside. Buckmaster ocf antennas are made from the best quality materials and are designed to give you years of troublefree service. Antenna basic concepts antenna an antenna is a device to transmit andor receive electromagnetic waves. Before we tackle the claims made about the ocf antenna, lets start by saying that it will work, but not significantly better than a dipole of the same length.
Understanding antennas for the nontechnical ham old. These are preliminary notes, intended only for distribution among the participants. Ictpituursi school on wireless networking for development the abdus salam international centre for theoretical physics ictp, trieste italy, 5 to 24 february 2007. Off center fed dipole antenna for the hf bands and 6 m, from 3 to 54 mhz. Building a simple multiband antenna that works, by the. Apr 29, 2010 so my plan is to build a new ocf dipole using the new 4.
In all cases 15m and the warc bands will require a tuner. The antenna works on the bands as advertised with low swr. This would increase the maximum coverage distance away from the router, allowing. So if you love to run around an antenna, naked, under the full moon after. Simplicity and effectiveness for a wide range of communications needs are.
This inspired author belrose, ve2cv, to reopen his files on the windom antenna, or, more properly, the offcenterfed dipole. The search for a simple broadband, multiband antenna with acceptable swr over the entire 8075meter band continued with the publication of the article by witt, ai1h, in april 1989 qst. Homemade carolina windom antenna m0ukd amateur radio blog. Ocf dipole 7 band 806 meters polystealth antenna ni4l. Basic antenna theory and application a major qualifying project report.
Antenna theory radiation pattern radiation is the term used to represent the emission or reception of wave front at the antenna, specifying its strength. An understanding of basic radio antenna theory will help the maximum be gained from any aerial system. The feedpoint impedance at the offset is at or about 200 ohms and the balun will provide good transformation to the coax feedline impedance of 50 ohms. Offcenterfed ocf dipole antenna for the national weather service.
Ocf dipole 7 band 80 6 rick on 27th mar 2018 you are not going to find a better antenna than this one. The 8band 300 watt antenna weighs 10 pounds and the 8band 3,000 watt antenna is 12 pounds. In any illustration, the sketch drawn to represent the radiation of an antenna is its radiation pattern. Basics of antennas giant metrewave radio telescope. Here are some typical ocf dipoles that are successful designs 1606 meter ocf antenna layout using a double tuned stub for better 20 and 40 meter performance here is the 1606 meter swr graph using 200 feet of rg2 feed line and an average height above ground. The analysis is carried out by using programs which are available on the internet.
Think of the carolina windom antenna the modern version of the windom as an upside down vertical antenna, hanging down from its counterpoise strung more or less horizontally some 10 meters or more above ground in other words, the 22 feet vertical component of the carolina between the 4. An antenna must be tuned matched to the same frequency band as the radio. In other words, the 22 feet vertical component of the carolina between the 4. The 7 band ocf dipole antenna was erected at 25 to 30 feet, on a hill side, using a military style push up mast, with a few customization on it. Study of the off centre fed dipole antenna g8ode short long feed point the off centre fed halfwave dipole the offcentre fed halfwave dipole, more commonly referred to as the ocfd, is very popular because it offers good performance as a multiband antenna using an antenna matching unit in conjunction with a 4. The offcenterfed dipole antenna design squash practice. In response, constantine balanis has updated his classic text, antenna theory, offering the most recent look at all the necessary topics. It is a halfwave long on the lowest frequency, and is fed from a coax cable. It must be made of durable, high quality, weather worthy components. Multiple leg length by two and by frequency on analyzer. Sep 05, 2015 building a simple multiband antenna that works, by the consultant hugh james latimer september 5, 2015 july 29, 2017 i consider the ability to communicate in a teotwawki scenario, and being able to obtain information outside the immediate area, critical.
Most antennas are resonant devices, which operate efficiently over a relatively narrow frequency band. Getting back on the air researched several wires which would fit my garden, tried a homebrew carolina windom and hey presto its a gem on all bands but top band. An antenna connected to a transmitter is the device that releases rf energy in the form of an electromagnetic field to be sent to a distant receiver. The antenna was described in qst and a commercial version was available at time of writing. Offcenterfed dipole antennas category is a curation of web resources on, ocf dipole, the six meter ocf sleeve dipole vertical, centerloaded offcenterfed dipole 6 band. During world war ii, as microwave theory became more popular amongst researchers, articles on aperture and horn antennas started to appear in academic journals. The theory is good but we need to translate it into practice. So for 80m and up, you have one leg that is 45 feet long, and another leg that is 90 feet long. Think of the carolina windom antenna the modern version of the windom as an upside down vertical antenna, hanging down from its counterpoise strung more or less horizontally some 10 meters or more above ground. Dont know the maths or the theory, but this antenna works as well as a g5rv. The fd4 80m10m antenna is modelled using mmanagal as shown above. Theory and construction of multiband antennas that cover multiple entire harmonic hf.
The study documents the behaviour of moving the feed point away from the centre of the halfwave 80m dipole in free space in order to simulate offcentre. The paper traces the history of antennas and some of the most basic radiating elements, demonstrates the fundamental. This is a popular antenna design as the performance is very good across the hf bands and requires little or no tuning. The ocf specification introduction and overview presentation has not changed as a result of the ocf 2.
The long end was tied to a tree, again, using insulated rope, and with maybe five. The normal windom is described as having a length leg, and a 23 length leg. This design exercise resulted in a new kind of antenna which i dubbed centerloaded offcenterfed dipole antenna, or clocfd for short. To build the ocf dipole in this case 8010m cut a single length of wire to an overall size of 3.
Antenna looks to be very well put together from high quality components. So my plan is to build a new ocf dipole using the new 4. The receiving properties of antennas are characterized by the antenna affective area af,t,i, where the available power at the output of the receiving antenna prf is the product of the effective area of the receiving antenna in direction t,i and the flux density swm2hz1 incident from that direction. We must position the feedpoint and select the antenna length to place the feedpoint at or near a current maximum at every desired operating frequency. Used a g5rv for years then had a break of some 20 years. The modern common windom antenna is not an original singlewire fed windom, but rather an offcenterfed or ocf two wire feed dipole. The national film board of canada for the canadian air forces great explanation of propagation. The initial antenna design is done with eznec, which sets the basic antenna parameters. The big advantage of this design is that you can make an antenna that does not require an antenna tuner by utilizing the constant impedance of the happy convergence that happens at 120 degrees. Ocf dipole antenna windom hf the offcenterfed dipole is a dipole whose feedpoint is at a point removed from the center of the antenna. Offcenterfed ocf antenna faq frequently asked questions q. Off center fed antenna, a dipole antenna with specific placement of feedpoint allowing multiple resonances in hf band. Ideally, the switched ratio balun should be connected to the end of the transmission line in an accessible and waterproof location.
Electromagnetic waves are often referred to as radio waves. Windom off center fed antennas radios amplifiers baluns. Ocf 8 bands 1606 hf windom polystealth antenna ni4l. For the king of common mode currents, the ocf dipole often called windom this will not be close. Balanis the discipline of antenna theory has experienced vast technological changes. Some tweaking may be needed, but mine was built within an inch or two of those measurements. Windom antenna, or, more properly, the offcenterfed dipole. The third reason is a desire to teach basic antenna theory to the average. Some antennas center fed and offcenter loaded small monoband. If feeding the antenna up to a ratio of d1d2 of is more convenient to the shack, then do so. So a point could be found, presumed to be 14% off centre, where the feedpoint impedance was 600 ohms.
Len carlson, k4iwl smithe windom six band hf windom antenna. Antenna fundamentals an antenna is a device that provides a transition between guided electromagnetic waves in wires and electromagnetic waves in free space. As the electromagnetic field strikes the receiving antenna, a voltage is induced into the antenna, which serves as a conductor. Thus the prime instrument of a radio telescope is the antenna. Hence, the best installation for an ocf is a matter of convenience. New material includes smart antennas and fractal antennas, along with the latest applications in wireless. Antennas antennas couple propagating electromagnetic waves to and from circuits and devices, typically using wires treated in section 3. An ocf dipole was designed for the national weather service so as to be resonant on even harmonics of 80 meters 804020. The ocf fd4 fd3 windom antenna fd4 80402010 m the 4band fritzel model fd4 is a special version of a windom antenna.
1423 669 611 203 1563 1137 1520 731 206 867 442 749 1098 989 929 1223 1320 415 569 394 851 556 1358 1383 1516 738 1038 1076 1569 10 621 760 109 1508 221 612 1031 453 910 535 771