Practical_Antenna_Handbook_0071639586

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C h a p t e r 2 9 : T o w e r s 673 Figure 29.8 Typical screw anchor. Screw anchors suitable for modest amateur tower installations can often be installed by hand, by screwing them into the ground with a long pinch bar or other strong steel rod threaded through the eye of the rod. But many tool rental outfits have gasoline-Â powered drivers that make the job easier. Another “glittering generality”: The harder it is to insert the screw anchor, the harder it will be for stressed guy wires to pull it out. Whether screw anchors or concrete pedestals are used, it is critically important to apply only longitudinal forces to the anchor rods, which have relatively little strength off-Âaxis. (Some commercially available rods can be bent sideways by hand!) Each guy rod should be installed at an angle that makes the combined force on it from all attached guy wires as close to perfectly in line with the axis of the rod as possible; typically, if the guy wires attached to various heights on the tower are all tensioned to the same specification, the angle of the rod should be equal to the average angle of the guy wires— typically in the 45-Âdegree range. Very little more of the rod than just the knuckle or attachment eyelet should be sticking up beyond the concrete pad or out of the earth. Failure to follow these rules will subject the anchor to the same kind of stresses discussed previously in conjunction with the steel post anchor. Each and every guy wire should have a turnbuckle at its lower end, just above the guy anchor. Two special tools are extremely helpful for proper tensioning of guy wires: • A come-Âalong for maintaining a temporary tension in a guy wire while securing the wire • A Loos tension gauge for tensioning the guy wires following installation
674 P a r t V I I I : M e c h a n i c a l C o n s t r u c t i o n a n d I n s t a l l a t i o n T e c h n i q u e s Come-Âalongs can be purchased at Sears, Home Depot, Lowe’s, and local hardware stores. The Loos can be obtained from Champion Radio Products or may be found at sailing accessory stores. There are only two acceptable types of guy wire material: EHS stranded galvanized steel and Phillystran®. Either can be obtained from the usual choice of antenna accessory vendors. The advantage of Phillystran is that it is nonconductive and long lengths of it do not need to be broken up by insulators to avoid resonances. When Phillystran is used, however, the bottom end of each guy wire must end in a length of EHS steel to avoid possible breakage from abrasion, vandalism, animals, etc. Steel guy wires come in many different diameters, each corresponding to a tensile strength rating. Generally, guy wires are tensioned (on a calm day) to some percentage (10 percent is common) of their maximum strength rating. That, of course, adds to the vertical force on the tower legs but ensures that the wires are not slack. (Guy wires that are not properly tensioned can allow tower tops to be snapped back and forth by wind gusts.) As discussed in other chapters, it’s a good idea to insert heavy-Âduty insulators of the proper compression strength in all guy wires if there’s the slightest chance the tower will ever be used as a vertical antenna (typically on 160 or 80 m). Retrofitting a tower installation with insulators is not fun. The tower itself can be directly grounded at its base and fed with shunt-Âfeed techniques described in Chap. 9. Ideally, all guy wires at a given height (or station) on the tower should come away at the same angle with respect to the tower or ground. When the land surrounding the tower base is not level, or when there is less space on one side of the tower than the other for positioning guy anchors, this isn’t always possible. Keep in mind that the top of the tower is in force equilibrium (i.e., stationary and vertical) only when the horizontal forces on it are equal and opposing. If guy wires come away at different angles with respect to the tower axis, it will take different tensions, T, in the three guy wires to produce identical horizontal components, T H . In other words, don’t try to make the tensions measured by your Loos gauge in the three guy wires identical if they come away from the same tower attachment height at different vertical angles. Once again, trigonometry is your friend when determining what tension to expect in each guy wire. Despite being made of rigid, strong steel sections, a tall, slender tower is capable of (often disconcerting) sideward movement far above its base. Blind tensioning of guy wires can lead to incorrect results, since applying too much tension to one guy wire will simply result in pulling the tower sideways at that guy wire’s attachment point until the horizontal forces at that guy station are again in equilibrium. Tensioning should always be followed by a check of the entire tower for trueness—such as by taking a carpenter’s level up the tower. However, during the tensioning process, standing or lying at the base of the tower and sighting straight up each face in turn should provide an exaggerated sense of straightness (but not whether it’s truly vertical!) to guide your subsequent tensioning activities while minimizing the number of trips up and down with the level. Historically, steel guy wires have been secured with cable clamps, but in recent years GUY GRIPS® have become popular, thanks to the speed and ease of their installation. Regardless of which method of securing guy wire ends you choose, there is only one “right way” but many “wrong ways”. Follow the manufacturer’s recommendations or refer to K7LXC’s book (see the end of this chapter).
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Practical Antenna Handbook
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Practical Antenna Handbook Joseph J
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Contents Preface . . . . . . . . .
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C o n t e n t s vii 12 The Yagi-Uda
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C o n t e n t s ix Switched-Pattern
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Preface My paternal grandfather was
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P r e f a c e xiii this book repres
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Acknowledgments As with other field
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Background and History Part I Chapt
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CHAPTER 1 Introduction to Radio Com
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C h a p t e r 1 : I n t r o d u c t
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Fundamentals Part II Chapter 2 Radi
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CHAPTER 2 Radio-Wave Propagation To
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C h a p t e r 2 : r a d i o - W a v
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R N-1 C h a p t e r 2 : r a d i o -
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Figure 2.29C Monthly averaged sunsp
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CHAPTER 3 Antenna Basics An antenna
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C h a p t e r 3 : A n t e n n a B a
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CHAPTER 4 Transmission Lines and Im
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C h a p t e r 4 : T r a n s m i s s
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Chapter 5 Antenna Arrays and Array
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C h a p t e r 5 : a n t e n n a A r
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A. B. C. D. E. F. G. H. Figure 5.9
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B. C. D. E. F. G. H. Figure 5.10 Gr
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High-Frequency Building-Block Anten
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CHAPTER 6 Dipoles and Doublets A co
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C h a p t e r 6 : D i p o l e s a n
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CHAPTER 7 Large Wire Loop Antennas
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C h a p t e r 7 : L a r g e W i r e
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CHAPTER 8 Multiband and Tunable Wir
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C h a p t e r 8 : M u l t i b a n d
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CHAPTER 9 Vertically Polarized Ante
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C h a p t e r 9 : V e r t i c a l l
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Quarter-wave vertical radiator Insu
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Directional High-Frequency Antenna
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CHAPTER 10 Wire Arrays When a singl
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C h a p t e r 1 0 : W i r e A r r a
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Wire 2 C h a p t e r 1 0 : W i r e
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CHAPTER 11 Vertical Arrays Despite
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C h a p t e r 1 1 : V e r t i c a l
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CHAPTER 12 The Yagi-Uda Beam Antenn
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C h a p t e r 1 2 : T h e Y a g i -
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CHAPTER 13 Cubical Quads and Delta
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C h a p t e r 1 3 : C u b i c a l Q
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Figure 13.5 Multiband quad “spide
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High-Frequency Antennas for Special
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CHAPTER 14 Receiving Antennas for H
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C h a p t e r 1 4 : r e c e i v i n
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351 Figure 14.12 Remote tuning sche
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CHAPTER 15 Hidden and Limited-Space
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C h a p t e r 1 5 : H i d d e n a n
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CHAPTER 16 Mobile and Marine Antenn
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C h a p t e r 1 6 : M o b i l e a n
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CHAPTER 17 Emergency and Portable A
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C h a p t e r 1 7 : E m e r g e n c
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Antennas for Other Frequencies Part
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CHAPTER 18 Antennas for 160 Meters
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C h a p t e r 1 8 : a n t e n n a s
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CHAPTER 19 VHF and UHF Antennas The
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C h a p t e r 1 9 : V H F a n d U H
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CHAPTER 20 Microwave Waveguides and
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C h a p t e r 2 0 : M i c r o w a v
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λ o = c / f 8 3× 10 m / s = 9 C h
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CHAPTER 21 Antenna Noise Temperatur
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C h a p t e r 2 1 : A n t e n n a N
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C h a p t e r 2 1 : A n t e n n a N
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CHAPTER 22 Radio Astronomy Antennas
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C h a p t e r 2 2 : R a d i o A s t
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Figure 22.9 Interferometer pattern.
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CHAPTER 23 Radio Direction-Finding
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C h a p t e r 2 3 : R a d i o D i r
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Figure 23.9 Adcock array RDF antenn
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Figure 23.11 Watson-Watt Adcock arr
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Tuning, Troubleshooting, and Design
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CHAPTER 24 Antenna Tuners (ATUs) Th
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CHAPTER 25 Antenna Modeling Softwar
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Figure 25.3B Bent dipole wire and s
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CHAPTER 26 The Smith Chart The math
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Figure 26.2 Normalized impedance li
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A Figure 26.3 Constant resistance c
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A Figure 26.4A Constant inductive r
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C h a p t e r 2 6 : T h e S m i t h
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D C B A Figure 26.5 Radially scaled
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0.165 Y ' 1.0 j1.1 G' 1.0 Y ' 0.2
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CHAPTER 27 Testing and Troubleshoot
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A p p e n d i x A : U s e f u l M a
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A p p e n d i x A : U s e f u l M a
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Appendix B Suppliers and Other Reso
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A p p e n d i x B : S u p p l i e r
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B.1.6 Rotators and Controllers Alfa
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Index Note: Boldface numbers denote
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I n d e x 747 Binns, Jack, first ma
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I n d e x 749 dipole (Cont.): slopi
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I n d e x 751 grounding and ground
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I n d e x 753 ionospheric propagati
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I n d e x 757 noise (Cont.): sky no
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I n d e x 765 vertically polarized
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I n d e x 767 Yagi antennas (Cont.)
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