Editor’s Note: OnAllBands is pleased to post a series of articles written by accomplished amateur radio contester and DX Engineering customer/technical support specialist Kirk Pickering, K4RO. The articles, originally published in the National Contest Journal from 2008-2011 and updated with current information, offer valuable insights for both contesters new and old.
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Welcome back to Contesting 101. In the last installment, we covered basic antennas for contesting. We discussed the importance of target areas and how we might use the patterns of simple antennas to work to our advantage. Knowing where to orient our antennas is important, but we also must know when we are most likely to have propagation to a target area on a given band.
One of the things that makes contesting interesting is the challenge of maximizing the use of available propagation. Not every band is open to every direction at every time, and the successful contester must learn which bands at what times can produce the best results. There are hundreds of books and thousands of articles devoted to the study of propagation, as well as propagation prediction tools. The reader is encouraged to explore the many resources available. In this brief article, I will attempt to cover very basic HF propagation as it relates to contest operating.
Follow the Sun
One of the best indicators we have for understanding propagation is the position of the sun relative to our location on earth. As the earth rotates along its axis, the sun illuminates one half, while the other half remains in darkness. Every rotation, of course, takes 24 hours and is how we define a calendar day. Different tools have been created over the years to help us understand the position of the sun, starting with the sun dial. As contesters, we are interested in seeing how the earth, as a whole, is illuminated. There are paper graphical tools to help such as the “DX Edge,” which was sold decades ago. Today, the Geochron Digital Atlas 3 4K World Clock with special Ham Radio Bundle includes real-time propagation layers for operators that allow tracking of the gray line and other benefits.
There are also three-dimensional globes which show the sun’s illumination on the earth. With the advent of the computer age, we now have programs such as Geoclock and various websites to help “show us the light” across the planet. Of particular use are programs capable of presenting maps in an azimuthal equidistant projection, centered on our location.
Editor’s Note: Some current propagation tools and resources are discussed in these OnAllBands articles, “Propagation Paths—The Long and Short of It” and “HF Propagation at the Equinox.”
The Ionosphere
The reason that we are so interested in the position of the sun is because of its effect on the ionosphere, a belt of charged particles surrounding the earth in the upper atmosphere. The ionosphere has a different composition when lit by the sun, compared to when it is not lit. The sun-lit area might typically have four layers, with the D-layer closest to earth, the E layer above that, and the F1 and F2 layers above that. In the areas of darkness, the D and E layers essentially disappear, and the F1 and F2 layers combine into a single F layer at night.
The density of these layers changes not only with the position of the sun, but also with the number of sunspots and the resulting solar radiation on any given day. Knowing that the layers exist is certainly interesting, but what really matters to contesters is the effect that the ionosphere has on radio propagation. In general, the more highly ionized the layers, the more they support the refraction (bending) of higher frequencies. More ionization also means more absorption (attenuation) on lower frequencies. The refraction of HF radio waves in the ionosphere is responsible for the “skip” phenomenon, allowing the magic of worldwide propagation to occur.
Follow the Maximum Usable Frequency (MUF)
One feature of the ionospheric refraction phenomenon is that different frequencies bend at different angles. Some angles are so slight that the radio wave does not return to earth. Generally, the higher the angle (more toward the zenith, or straight up) the shorter the skip. Likewise, the lower the angle (toward the horizon) the longer the skip. For a given target direction, there is an upper frequency limit at which communication can occur. This limit is called the Maximum Usable Frequency, or MUF. Propagation tends to be best at the MUF, so it is important for the successful contester to be aware of the MUF at any given time. (Editor’s Note: The Geochron bundle mentioned above provides MUF visualization.)
Learn by Operating
It simply can’t be said enough. The best way to learn about propagation is to be in front of the radio as much as possible during contests and any other time that you can operate. Each hour will present different conditions as the earth rotates along its axis. Some contesters describe DX contests as “watching the earth turn.” We will go through an example of a typical DX contest effort from middle Tennessee. The exact times and band openings will be different for each location, but hopefully this will give an example of the kinds of patterns to look for. For the purposes of demonstration, we will assume some decent conditions for our example contest, with enough solar flux to support reliable openings on 10 meters to Europe. We will only describe one solar day. Note that in a 48-hour DX contest, conditions often will vary considerably between the two days, but the same general patterns apply.
Typical DX Contest Openings
0000-0200z—Contest Start Time
The sun has set in middle TN, but because of the decent solar flux, western paths are still open on the high bands. There is plenty of sunlight illuminating the path between TN and JA, and JA signals are loud on 15 meters. The only signals heard on 10 meters are from South America, an indication that the MUF toward JA is somewhere above 21 MHz but below 28 MHz today. No signals from Europe are heard on 10 or 15 meters. The path of complete darkness between TN and EU means that the denser layers of the ionosphere have dissipated, and the MUF to EU is well below 20 MHz. We are hearing some EU on 20 meters and hearing EU quite well on 40 meters. As a single operator, we must make a choice: work JA on the high bands or work EU on the low bands. I would probably milk the 15M opening to JA first and then switch to 40M for EU after the high bands close to Asia. The openings to Asia are rarer and less reliable from middle TN. The same opening might not exist on day two, so we will choose to “make hay while the sun is shining.”
0200-0400z
The high bands have closed to Asia, and the only target population center open is Europe on 40 meters. Eighty meters is also starting to open to Europe—especially eastern Europe. Our sunlight map program shows us where the terminator or gray line is located. The gray line is the area between sunlight and darkness—either dawn or dusk—which constantly turns across the globe as the earth spins. Stations located along the gray line often experience enhanced propagation as the terminator crosses over. The astute contester will keep their eye on the gray line and pick up some nice multipliers on the low bands. ‘
0400-0600z
As the sun comes up across the European continent, signals on 80 and 160 meters reach their peak signal strength. With a careful eye on the gray line, it should be pos…
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