Practical_Antenna_Handbook_0071639586

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404 p a r t V I : a n t e n n a s f o r O t h e r F r e q u e n c i e s within the ATU itself may be less than the reduction in transmission line losses from high SWR, and it may also represent the only way to get full performance and/or legal power from the transceiver or amplifier feeding the line. Shortened Verticals The antennas in this section are all variations on the basic l/4 vertical of the preceding paragraph. In general, each is a shortened monopole augmented by distributed and/or lumped-constant circuit elements to keep the radiation efficiency as high as possible and to minimize the VSWR on the transmission line back to the transmitter. Again, these antennas will not work quite as well as a properly installed full-size antenna, but they will serve to get you on the air with a very passable signal from cramped quarters that would otherwise preclude operation on these frequencies. Several different popular configurations are shown in Fig. 18.1. The basis for all these antennas is a vertical that is physically short as compared to the “standard”: a quarter-wavelength (l/4) (i.e., 90-degree electrical length) monopole with an ideal ground plane beneath it. Recall that a vertical monopole too short for its operating frequency (i.e., less than l/4) will exhibit capacitive reactance. In order to resonate such an antenna, it is necessary to cancel the capacitive reactance with an equal amount of inductive reactance, such that |X L | = |X C |. By placing an inductance in series with the radiating element, therefore, we can effectively “lengthen” it electrically, as measured at the feedpoint of the combined antenna element and series inductor. An antenna that is reactance-compensated is said to be loaded; in the preceding example, the antenna is inductively loaded. Three generic forms of loading are popular: discrete loading, continuous loading, and linear loading. Discrete loading means that there is a discrete, or lumped, component (inductance or capacitance) connected to the antenna radiator. The simplest form of inductive loading inserts a loading coil near the center (Fig. 18.1A) or at the base (Fig. 18.1B) of the radiator element. Because there is very little current near the open circuit end of a vertical, inductive loading at the top does little; instead, a capacitive hat (Fig. 18.1C)—often in conjunction with a center loading coil—is much more effective at increasing the area under the current-versus-length curve. You may recognize these configurations as being the same as those found on mobile antennas. Indeed, low-band mobile antennas can be used in both mobile and fixed installations. Note, however, that although it is convenient to use mobile antennas for fixed locations (because they are easily available in “store-bought” form), they are far less efficient than other, longer versions of the same concept. The reason is that the mobile antenna for the lower HF bands has historically been based on the standard 96- to 102-in whip antenna used by amateur operators on 10 m or by citizens band operators on 11 m, with the overall height of the antenna limited by safety and mounting considerations. In fixed locations, on the other hand, longer radiator elements (which are more efficient) are usually possible. For example, a 16- to 30-ft-high aluminum radiator element can easily be constructed of readily obtainable materials. Loaded antennas tend to be rather high Q devices, and their bandwidth is quite narrow. An antenna tuned for the center of a band may present a high VSWR at the ends of the band—especially on 160 m, where the U.S. amateur band extends ±5 percent from the center frequency. One way around this problem is to make the inductor variable, so that slightly different inductance values can be selected for different band seg-
C h a p t e r 1 8 : a n t e n n a s f o r 1 6 0 M e t e r s 405 To XMTR To XMTR To XMTR A B C To XMTR To XMTR D E Figure 18.1 Examples of loaded vertical antennas. (A) Center. (B) Base. (C) Top. (D) Continuous. (E) Linear. ments. On 1.8 Mhz this is probably easily accomplished only for the base-loaded version (Fig. 18.1B). For the other configurations, it is far easier to use an adjustable matching network or ATU at the base of the antenna. A continuously loaded antenna has the inductance distributed along the entire length of the radiator (Fig. 18.1D). Typical of these antennas is the helically wound vertical, in
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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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Page 395 and 396: CHAPTER 16 Mobile and Marine Antenn
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Page 409 and 410: CHAPTER 17 Emergency and Portable A
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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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C h a p t e r 2 4 : a n t e n n a T
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CHAPTER 25 Antenna Modeling Softwar
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C h a p t e r 2 5 : A n t e n n a M
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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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C h a p t e r 2 7 : T e s t i n g a
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Mechanical Construction and Install
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CHAPTER 28 Supports for Wires and V
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C h a p t e r 2 8 : S u p p o r t s
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CHAPTER 29 Towers At some point, th
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C h a p t e r 2 9 : T o w e r s 655
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CHAPTER 30 Grounding for Safety and
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C h a p t e r 3 0 : G r o u n d i n
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CHAPTER 31 Zoning, Restrictive Cove
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C h a p t e r 3 1 : Z o n i n g , R
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C h a p t e r 3 1 : Z o n i n g , R
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Appendices
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APPENDIX A Useful Math The material
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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 755 maximum effective len
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I n d e x 757 noise (Cont.): sky no
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I n d e x 763 transmission lines, 1
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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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