Some Notes on NVIS Antennas

About a decade ago, I placed some casual notes on NVIS antennas under the present title, using the term "cloud burner" as it was once used to describe these antennas. The intervening years have produced two important developments. One has been the emerging realization that near-vertical incidence skywave (NVIS) propagation has a very significant role to play in emergency communications, especially for major natural disasters that eliminate most of the up-to-date communications modes. Amateur operations following a pair of major hurricanes in the U.S. gulf coast region demonstrated the importance of this communications mode, a fact that the U.S. and other military organizations had begun to realize as early as in World War II.

The second development is personal. Over the decade since the early notes, I have accumulated a considerable body of modeling data born of my interest in seeing how much of NVIS antenna talk was correct and how much was in need of correction. The original notes that filled this space did not so much require amendment as they needed very serious supplementation. The additional material consists partly of more thorough investigations into the radiation properties of NVIS antennas for 75 and 40 meters, the two most popular amateur bands for NVIS operation. Mythologies and sound bites concerning the ideal height for a NVIS antenna required not a single replacement value, but an exploration of ideal heights for various types of antennas over various ground qualities. Indeed, the role of ground quality has received scarce attention up until recently.

At the bottom line relative to this site, the result has been the development of a series of notes on the fundamentals of NVIS antennas, with emphasis upon the most basic NVIS antenna types: the dipole, the inverted-V, and the 1 wavelength loop. Each collection of notes uses the PDF format. At present, the collection includes the following items.

• 1. NVIS Propagation and Antennas: Some Background Basics: a review of NVIS propagation and other background information necessary for the effective use of subsequent notes
• 2. Basic NVIS Antennas: Dipoles, Loops, and Vs: a survey of the basic radiation properties of fundamental antenna types on various bands and over various types of ground quality
• 3. Basic NVIS Antennas with Reflectors: Dipoles, Loops, and Vs: an examination of the properties of both parasitic and planar reflectors for basic NVIS antennas
• 4. Practical Basic NVIS Antennas: Dipoles, Inverted-Vs, 1-Wavelength Loops, and Doublets: a survey of practical NVIS antennas, including both monoband and 2-band antenna forms
• 5. Some Basic Fixed 3-Band NIVS Antennas: A sampling of techniques for including 75, 60, and 40 meters in NVIS antenna coverage
• 6. Special Purpose NVIS Antennas: A sampling of some special purposes antennas, such as those with perfectly circular patterns, those having maximum usable gain, and those capable of tilting the NVIS radiation pattern

As the entries suggest, the list of possible topics is far from closed. However, I hope that the notes provide some useful data on NVIS antenna properties for anyone planning a fixed-station installation. These antennas have become a significant part of amateur contributions to emergency communications.

Updated 03-15-1998, 01-12-1999, 03-15-1999, 11-05-2002, 02-20-2008, 02-23-2008. © L. B. Cebik, W4RNL. Data may be used for personal purposes, but may not be reproduced for publication in print or any other medium without permission of the author.

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Topics: Dipole, Doublet, HF Lower, Horizontal Loop, Inverted V, Moxon, NVIS, Traps, Yagi