FARS - Articles by Steve Stearns, K6OIK
Antenna Potpourri [2.0 MB]
ABSTRACT: Cats feature in some famous explanations of radio. Examples are given. Antenna Q has multiple definitions. A fundamental definition of Q is given. One kind of formula for Q is shown to be wrong. Chu’s famous 1948 result on antenna Q is revisited and shown to be correct but incomplete. A correction is given that generalizes Chu. One kind of formula for Q is shown to be wrong. Finally a comparison of HF dipoles versus verticals versus horizontal and vertical loops over ground shows which is better and why. No, it is not just a matter of pattern shape or noise polarization.
ABSTRACT: If you buy too much ham stuff, your house will overflow with Amateur Radio equipment. Steve, K6OIK shows how to continue collecting ham stuff even if your house is overflowing. The secret is to collect stuff that occupies no space. Radio information, in the form of articles, papers, books, or other publications, is available online. Whether it is an article from Popular Electronics, a home-study course from National Radio Institute, a book on antennas, an NAB Engineering Handbook, or papers from the IEEE or Bell System Technical Journal, it is available online if you know where and how to look. Steve shows the sources of information (software, archival articles, papers, and books) that Google often fails to find and yet is free and occupies no space other than on your hard drive.
ABSTRACT: Series and parallel RLC resonant circuits have long been the staple equivalent circuits for dipole and loop antennas despite being narrowband approximations. This paper shows how to make universal equivalent circuits for any antenna over any bandwidth. Part 1 introduces the history of classical electric network synthesis and Smith charts and reviews antenna impedance and admittance properties. Part 2 explains the modes of vibration of continuous structures, natural frequencies, feedpoint current, and impedance resonances. The impedance function of any antenna can be accurately modeled by two of four universal equivalent circuits given computed or measured impedance data and a circuit optimizer. Examples of broadband universal equivalent circuits are shown for dipole, circular loop, and discone antennas over multi-octave and decade bandwidths. Broadband equivalent circuits are useful for interpolating between data points and performing lab tests without radiating. 1-port equivalent circuits are useful for making dummy loads for reflection experiments or match network testing. 2-port equivalent circuits are useful for making emulators for transmission tests.
The Shape of Antennas Yet to Come [3.6 MB]
ABSTRACT: Steve Stearns, K6OIK, talks about optimizers beginning with this puzzle: A ham wants to make a wire antenna for 20-meter DX. It needs to have a lot of gain. More gain is better. He is blessed with an infinite spool of antenna wire but cursed with rusty, old wire cutters. He can make but two cuts. He cuts off two pieces of wire to drive one against the other. How much gain can his antenna have? In answering this simple question, Steve leads us beyond dipoles into a world of 2D paths in 3D space. You will throw away your wire cutters after Steve shows how Texas longhorns and cowboy hats can beat beams.
ABSTRACT: HOBBIES (acronym for “Higher Order Basis Based Integral Equation Solver”) is software for computational electromagnetic analysis. It is a great tool for modeling antennas, arrays of antennas, coupled transmit and receive antennas, and scattering problems. HOBBIES E&M algorithms are similar to those in the professional program WIPL-D. Due to efficient software architecture and numerical algorithms, HOBBIES can handle very large and complex models on a desktop or laptop computer, for which other software programs would require a supercomputer. The best part is that HOBBIES is inexpensive.
Dipole Basics (rev 1) [5.8 MB]
ABSTRACT: The dipole is the most basic of antennas. A proper understanding of dipole properties and characteristics is essential to understanding many other antennas including complementary antennas such as slots. In this tutorial, Steve Stearns, K6OIK, explains the basic characteristics of dipoles for transmitting and receiving. Some surprises await as we learn that a dipole’s transmit current distribution is not exactly sinusoidal, and the receive distribution is entirely different. Steve explains the physics of the much misunderstood dipole shortening factor K. And why a dipole’s effective receiving capture area is different from its physical cross-sectional area. And that resonance is a poor indicator of match. Steve indicates which dipole properties are better determined from graphs and equations, and which other properties are better determined by numerical computation, known as modeling.
Antennas: The Story from Physics to Computational Electromagnetics (rev 2) [7.4 MB]
ABSTRACT: Steve Stearns, K6OIK, reviews the history of antenna analysis that led to modern computational electromagnetics. He reviews the shift from general physics to antenna engineering. Steve tells the surprising tale of the mysterious multiplying factor K that defines dipole resonant length and reveals why the ARRL and RSGB graphs of K still disagree after 71 years! Antenna modeling programs that are free or inexpensive are listed. Various programs have different capabilities to handle geometric shapes and materials, or show results as graphs, 3D depictions, or animations of full-wave simulations. Steve explains meshing by 1D segments, 2D surface patches, and 3D voxels. Many computed examples confirm and refute ideas about loading coil fields and resonances, wave propagation over irregular terrain, and antenna performance on spherical earth, as well as fields inside dielectric objects. This presentation shows the power of modern computational electromagnetics to illuminate our understanding of electromagnetic phenomena and to analyze diverse problems in antenna engineering and Amateur Radio.
Antenna Modeling for Radio Amateurs [8.1 MB]
ABSTRACT: In this updated version of his popular 2016, and 2008 presentations, Steve Stearns, K6OIK, addresses these topics: Where do antenna modeling programs come from, how do they work, what are their limitations, what is the state of the art? These questions and others are answered by Steve Stearns, K6OIK, in this tutorial introduction to antenna modeling. Steve reviews the historical timeline of events that led to modern computational electromagnetics. Steve tells which antenna modeling programs are free or inexpensive, the capabilities of different software to handle various shapes, materials, near field structures (like the Earth), and which can present results as graphs, 3D depictions, or movies of full-wave simulations. Also covered is meshing by 1D segments, 2D surface patches, and 3D voxels needed to compute fields inside inhomogeneous dielectric objects such as people. This presentation shows the power of modern computational electromagnetics to solve practical problems in antenna engineering and Amateur Radio, and suggests what the future may hold.
ABSTRACT: Terrestrial radio, TV, cellular, and wireless systems are not “line-of-sight” despite what you've heard. Otherwise, your HT and smart phone would not work indoors, and your WiFi router’s signal would not reach other rooms. Today, powerful computer programs are used universally to design uch systems. The hard part of the calculation is to determine RF path loss while properly accounting for reflection, refraction, diffraction, and shadowing effects. One algorithm, the Longley-Rice algorithm, was developed to specifically model radio propagation over irregular terrain. This algorithm became the basis for the government's Irregular Terrain Model (ITM) software, which, in turn, was adopted by the FCC as the approved method for computing service contours and interference between fixed stations. Steve, K6OIK, reviews propagation theory, prediction algorithms, and shows how to compute the two-way service contours of repeaters for high-reliability communication and for mountain top DX fun.
Weird Waves [1.5 MB]
ABSTRACT: Little-known solutions to Maxwell's Equations, called “localized waves,” include electromagnetic vortex waves, knotted waves, and linked waves. These waves are introduced and their unusual properties and behavior are explained. Among the amazing applications, the most intriguing for Amateur Radio is DX without ionosphere. Some serious new developments in antenna theory could make this possibility real.
ABSTRACT: “The Joy of Matching” is a tutorial introduction to the concepts and methods of impedance matching network design. Topics include what impedance is, what impedance functions are, characteristics of passive, active, and antenna impedance functions, the Smith chart, and the advantages and disadvantages of conjugate impedance matching. Steve, K6OIK, shows how a Smith chart allows one to visualize and predict a network’s impedance-transforming behavior without math. Steve starts with simple L-networks made of lumped elements or stubs, and progresses through ladder networks to more complicated network topologies. He show solutions to a variety of impedance matching problems: matching at a single frequency, matching at several frequencies simultaneously, and matching a continuous band of frequencies. The Fano limit on the match bandwidth of passive loads like antennas is explained. Two tricks are shown for exceeding the Fano limit: passive reflectionless match networks and active non-Foster match networks. Free or inexpensive software for match network design is recommended.
ABSTRACT: Every Radio Amateur knows that transmission lines support waves in two directions. Therefore every Radio Amateur “knows” that if a forward wave carries forward power, and a reverse wave carries reverse power, then net power delivered is the difference between the two. Right? In fact, at Pacificon 2010, the author showed how this simple idea leads to “proof” of the published equation for total loss of a mismatched, lossy transmission line. The author now presents a transmission line paradox in which the “proved” equation fails to give the right answer. In resolving the paradox, we discover the published equation is correct only in special cases. A more accurate and general expression for total line loss is given. A comparison between the published and new loss equations shows the former can have large error. The author shows how to think about and compute transmission line power transfer and loss.
ABSTRACT: Your antenna has a Q, and it is a function of frequency. What is it? How can you measure it? Why does it matter? Antenna modeling programs won't tell you the answer. However, these are some of the questions I answer as we explore the most abstract and least discussed fundamental property of antennas. This talk is sure to raise your I.Q. on your antenna's Q.
ABSTRACT: A discussion of many different kinds of filters that use transmission lines as 1-port devices (stubs) and 2-port devices. The filter design problem is introduced as an extension of match network design on the Smith chart. The differences between reflection filters and absorption filters is explained. Transmission line filter types introduced include simple stubs, hybrid with lumped elements, sub-harmonic stub filters, reflectionless stub filters and diplexers, commensurate stub filters, and two kinds of reentrant filters. Highlights include a variety of practical transmission line filters, a Field Day filter to isolate the 20-meter CW and phone sub-bands, and a reentrant diplexer filter that CBS and Mackay Radio used to feed two 50-kW transmitters into a single broadcast antenna.
Conjugate Match Myths [1.3 MB]
ABSTRACT: Examines the effect of lossy transmission lines on SWR and the effects of mismatched loads on power transfer. This examination demonstrates that conjugate matching for maximum power transfer as described by Walter Maxwell is incorrect for lossy transmission lines.
Facts about SWR and Loss [1.7 MB]
ABSTRACT: While much of conventional transmission line theory deals with lossless lines, such lines are but theoretical abstractions. Real transmission lines have loss, and some have high loss. Steve Stearns, K6OIK, covers the effect of loss on SWR and power transfer from a transmitter to an antenna. He explains the sometimes confusing graphs that have been published over the years and gives new ones that are more useful. He explains the difference between Zo matching and conjugate-impedance matching. He presents new results on maximum power transfer, which show that some popularly published ideas are not entirely correct. Finally, he shows how to maximize power transfer through a real, lossy line and explains the conditions when it should not be done.
All About the Discone Antenna [6.2 MB]
ABSTRACT: This talk is divided into three parts: uniform transmission lines, the Smith chart, and matching networks. In Part 1 we review the historical development of uniform transmission lines. Topics covered are: line synthesis; the calculation of transmission line parameters from geometry, dimensions, and material properties; various “optimum” coax dimensions; impedance transformations, and the properties of special lengths of line, such as half-, quarter-, and eighth-wave lines. We show how to use an antenna analyzer to measure the characteristic impedance and velocity factor of a transmission line. In Part 2 we introduce the Smith chart and show that in addition to being an intuitive graphical method for solving complex impedance transformations, it can also be used as a nomogram for basic math calculations. In Part 3, we discuss the reasons for matching, the best ways to match, and the design of single-frequency, multiple-frequency, and broadband matching networks.