Note that the better ground conditions give a lower angle. Droop angle the graph on the right shows the effect of an increasing angle of droop. Additionally, ive read a paper which claimed that the gain of the antenna changes periodically with the ground plane size. Advantages the elevated radials greatly reduce ground losses when compared to a ground mounted vertical antenna.
Radial slowly twist the wire while pulling it to keep it taught. Ground plane and antennas electronics forum circuits. A ground plane antenna project for 10 meters band by n4zaw. Ground mounted antennas are often very easy and convenient to use. A simple ground plane antenna you can buildfor 146, 223 or 440 mhzin no time flat. A represents the curve under perfect ground conditions, b under average ground conditions i. The vertical antenna is a monopole antenna, not balanced with respect to ground. A ground plane antenna is a form of dipole antenna designed to work with an unbalanced feed line. For 2 meters, however, top mounting on an rv is an excellent choice, as long as you provide an adequate ground plane. A poor mans antenna analyser the rsgb and radcom were given priority over publication of this article, but after many months of inaction, i have decided, for the benefit of fellow amateurs, to publish it myself on this website.
A ground plane antenna by definition gives you a ground plane, but still, if you antenna has a good ground plane there should be only marginal deferences. This paper presents the effect of the slots in ground plane and patch on resonant frequency, impedance bandwidth, gain and side lobe. Groundplane antennas for 144, 222 and 440mhz for the fm operator living in the primary coverage area of a repeate r, the ease of construction and low cost of a 14. Eventually at an angle of 90 the radials will combine and the ground plane antenna becomes an vertical dipole and exhibits an impedance of 75. Does anyone with experience relating ground plane size to antenna gain know of any useful resources. Before starting to build the antenna, you can stiffen up ordinary 14 gauge copper. The antenna is completely enclosed in a 4foot 34inch pvc pipe. Study of the quarter wave vertical 20m antenna with. The firestik firefly lg3m2lg4m2 no ground plane antenna kit with molded side mount is a great antenna kit for rv or any other. Concentrated ground plane booster antenna technology for. A 12 wave antenna isnt dependent on a good ground, it isnt as prone to lose power in a poor ground situation. Now cut the required part until it looks like the following picture. Place the active antenna on top and solder a small wire from the aluminium cage on the antenna to the copper of your. When tested with my 2meter ht and vhf wattmeter at 147.
How to ground an antenna antenna rf ground antenna ground plane knowing how to ground or earth an antenna system can be a key factor in the operation of some antennas. There are many comparative evaluations suggesting that there is often little difference in performance with the 5. If you were to flip the antenna upsidedown, ideally with no part of the antenna touching the ground, then your antenna radiation pattern wouldnt change all that much, as youve discovered on eznec. Ngp no ground plane antennas at cb world no ground plane ngp antennas. I observed that as i increase the ground plane size, the gain increases at first and then decreases. Pay no attention to the wire goingoff horizontally from the base. Ease of fabrication and cost makes the ground plane antenna one of the popular antennas in communication systems. It is ideal for technician class hams needing a first antenna, and also a very good emergency antenna for use during skywarn events when you dont want to be on the sky hooks tall in the sky. The antenna is resonant and a good match for 50ohm cable. Pdf modified ground plane of patch antenna for broadband. The ground or any large conductive surface plays the role of the second conductor of a dipole. The na4it cheap dual band ground plane antenna here is a neat little antenna that is very easy and cheap to build. Far field issues further out from the antenna, the reflections from the ground either add or subtract from the direct signal from the antenna, depending on the phase relationships. The daughter of a millionaire refused to marry a poor man and this is what he did duration.
Radial attach each radial with a 632 screw, lockwasher and nut 20. In addition the metal ground plane will support surface waves 11, 12. Study of the quarter wave vertical 20m antenna with elevated. As it was demonstrated in 1420, the antenna bandwidth can be improved by achieving a ground plane length of approximately 0. This looks much easier, and should not need as much guy wire tie down. When 8 radials are used instead of 4, the swr improves to 1. Vhf and uhf antenna systems 1821 fig23these drawings illustrate the dimensions for the 144mhz ground plane antenna. It features wireend loops for safety sharp, straight wires are hazardous and convenience its top loop lets you hang it off high objects for best performance. Mobile antennas base loaded no ground plane antennas pctel, inc. As the name indicates the antenna ground plane acts as a. However when it is not possible to ground mount an antenna because of ground conditions or it is necessary to elevate the antenna, another solution is to use a ground plane. Meanwhie the takeoff angle appears to be in the range of 15 to 20 degrees for most cases at low heights.
The concept of a ground plane is roughly to build a antenna half as long as a normal selfcontained one, then add a mirror so that it looks like a complete antenna from the antenna side of the mirror. A ground plane must satisfy both length and width dimensions outlined below. Does mounting a ground plane antenna upside down change the. When mounted on the 4radial portable ground plane described above, the same antenna shows 1. The reason of the poor return loss is due to the ground plane which is close to the spiral arms, therefore, the ground plane surface has a 1800 reflection phase and the image current image current is the current of the image of spiral antenna, which is formed by the waves reflecting from the conductive ground plane has an opposite. Knowing how to ground an antenna properly can make significant improvements to its performance, whereas a poor ground or earth connection can mean that its performance is greatly. In a monopole antenna, the radiation pattern of the monopole plus the virtual image antenna make it appear as a two element centerfed dipole antenna.
On a metalskinned rv its a great place, if you dont drive down many tree lined avenues, or eat at drivethrough restaurants. Its just one end of my g5rv dipole, or sometimes called a dummy load. Modified ground plane of patch antenna for broadband applications in cband article pdf available in microwave and optical technology letters 585. Surface waves will radiate vertically if scattered by bends, discontinuities i. A basic antenna like a dipole is selfcontained and requires no ground plane. Use tape to hold the parts on the noncopper side together and fold the corners to they met. A little girl boarded a plane with a stranger, 15 years later something. Pdf effect of slots in ground plane and patch on microstrip. A poor man s antenna analyser with sincere thanks to that outstanding engineerdesigner, jim tregellas vk5jst 1, whose original work inspired me, for his patience, advice, understanding, tolerance and good humour in answering my many emails instead of telling me where to go.
Thank you for all those questions, please keep them coming. Your 2 meter mobile antenna whats the best mounting location. A ground plane is not a metal roof gutter, a window frame, a downspout or any other piece of metal that is long and thin. Measurements are compared to a rubber duck, ground plane, and standard 12v jpole. Effects of ground plane size on antenna gain electrical. The gain for the ground plane is very nearly constant and equal to an isotropic antenna at low heights and real ground conditions. If you try to use standard ground based cb equipment with a vehicle or in a situation that requires a no ground plane antenna, youll likely experience both high swr levels and extremely poor performance. Since monopole antennas rely on a conductive surface, they may be mounted with a ground plane to approximate the effect of being mounted on the earths surface. Study of the quarter wave vertical 20m antenna with elevated ground plane explanation of the models calculated swr an swr of 1. Two things have changed compared to a normal ground mounted vertical. Sounds like a poor man s rc292 from my old days in the us army, we could reach out and talk to folks with one of those rigs, but we needed adjustable so we had regular screw together antenna parts, with three ground plane antennas on the out side. The concept of suppressing surface waves on metals is not new.
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