DX'ing around local sunrise and sunset can be extremely profitable to the DX'er in terms of new loggings, and there are several helpful methods to be explored for taking full advantage. First and foremost, you need to have a set of sunrise/sunset maps, which are available from the NRC Publications Center [ Item SSM, $3.50 to members ]. For each calendar month, the FCC has established specific times for stations to change from their authorized daytime facilities over to their authorized nighttime facilities, or, if a daytimer, to sign off. [ Note: use of the term 'facilities' includes transmitter powers and antenna patterns; in a few cases separate transmitter sites are used for day and night operations.] Stations are grouped based on quarter-hour segments falling closest to the actual sunrise and sunset times at the individual locations. The zones shown on the maps represent these groupings. It should be noted, however, that there are multiple exceptions to this general statement. Many stations also have specific and often different facilities authorized for use during Critical Hours (CH), Canadian Restricted (CR), Pre-Sunrise Authority (PSA) and/or Post-Sunset Authority (PSSA). [ Note: definitions for these terms may be found in the front of the NRC Domestic Log. The way in which different combinations of facilities are assigned dictates the operations codes such as 'U3' or 'D1' used in the Log.] The DX'er should enter the hour designations onto the maps either for the home location, or in such other standard time as you prefer.
Owing to the direction of the Earth's rotation, both sunrise and sunset appear first at the eastern side of the continent, and gradually progress westward. This means that DX'ers located in different parts of the continent must approach sunrise and sunset DX somewhat differently. DX'ers located on or near either coast have no stations ( either targets or sources of interference ) located in one or more directions, whereas DX'ers located in most of the rest of the country can look forward to DX'ing through the approach and passing of local sunrise or sunset.
What actually occurs at these times is a result of the differing medium wave signal propagation characteristics of day and night. As either sunrise or sunset approaches and passes the DX location, these propagation characteristics change. During the day, groundwave propagation predominates, and reception beyond 1000 miles is rare during the winter and nonexistent during the summer. At night, for all but the most powerful and/or closest stations, the predominant type of propagation becomes skywave, where signals are refracted by layers of electrically charged particles located in the ionosphere. Thus, as sunrise approaches, more distant receptions to the east of the DX location begin to diminish, and, as sunrise moves to the west, distant reception from the other directions also diminishes. As sunset approaches, the reverse situation occurs.
Of course, a look at the sunrise/sunset maps will illustrate that in most months the effects aren't simply 'east vs. west', as the earth's rotation and orbit around the sun create month-to-month variations such that the pattern may actually be 'northeast vs. southwest' for example. But this is part of the fun and also the challenge of this aspect of the hobby, because the pattern changes every month, along with the changeover times, the zones themselves, and, as a result, which stations fall into which zones.
Once you are familiar with the maps and how they illustrate these patterns, it's time to decide which frequencies you'll want to concentrate on. But don't be too quick to eliminate frequencies occupied by strong locals unless they are very strong, because one of the side effects of sunrise/sunset DX is that in many cases these may be the only times (and only during the late Fall through early Spring months) when it may be possible to hear anything underneath these locals. [ Note: in many cases, some sort of a gain or directional antenna will be required to do this, but there are times when stations may appear along with the locals even without such antennas. ] Two separate lists will be required - one for sunrise and another for sunset.
The first consideration in making such a list today is dramatically different from what was the first consideration 20+ years ago, as a result of the proliferation of fulltime operations, PSA's, and PSSA's where there were once mostly daytimers. Many DX'ers can remember when it was possible to DX from the northern part of the east coast and hear stations all the way to California on 1580, and well into the west on 1570! Back then, aside from a handful of fulltimers in Canada or Mexico, these channels contained nothing but daytime stations, and signoffs could be followed in sequence across the country. Today, making a target list is much more complex, as not only are there fulltime stations on most frequencies, but there are also increasing numbers of stations which remain on with their daytime facilities well into the night, although Pacific Northwestern DX'ers still hear stations along the East Coast near sunrise using directional antennas.
The target list should start with frequencies where you have no strong locals, and where even at night it is possible to hear more than one station. You'll also probably want to eliminate any frequencies adjacent to your most difficult pests. Next, you'll need to see what stations there are which you might reasonably be able to hear at sunrise or sunset.
Start with stations whose sunrise or sunset time is no more than one half hour different from that at your QTH, and also within about 300-400 miles. Now review the lists to see if any of the stations you've selected as targets are likely to be covered by a regional station on the same channel with higher power or closer to you, and if so, move those to the bottom of your list. You can expand beyond these parameters later on.
In order to maximize your potential for successful sunrise/sunset DX'ing, you'll need to review your target stations along with any co-channel or adjacent channel interference possibilities against the maps on a month-by-month basis across the DX season. One way to do this is to photocopy the maps and then actually plot in the locations of target stations. Because most of your targets will be within a relatively concentrated geographic area, you may need multiple copies of the maps. To conserve space, use numbers or letters to correspond to the target stations to identify the points on the maps.
Your target stations should fall into the following categories: daytime stations signing on or off, fulltime stations having significant power and/or pattern changes between day and night, and stations where an interfering station's sunrise or sunset time may differ from those of the target station so as to permit reception. Remember, though, that through all else, conditions on specific frequencies and along specific paths can vary considerably from day to day as well as month to month, and sometimes it may take time to hear some of the stations on your list. Unfortunately, too, there are always some which may either never be heard or be heard only by some unusual chance occurrence such as another station going off the air, or your target station remaining on day facilities unexpectedly.
As you DX at sunrise and sunset more frequently, you will also discover that there are other patterns to your receptions. You'll learn that in the Fall, when the days are getting shorter, your best receptions will come near the end of the month, when daylight is the shortest relative to the monthly average, and that in the months after the Winter Solstice, the best receptions come toward the beginning of the month for the same reason. You'll also discover that stations in the located closest to the eastern zone boundary will often be stronger than those at the western one at sunset, again owing to a slightly earlier actual sunset as compared to the monthly average. At sunrise, however, this works in reverse, because it is the light rather than the darkness that is moving westward.
Also, it pays to remember that auroral conditions impact DX at sunrise and sunset, which will usually present receptions from southerly directions that would otherwise be unheard or eliminate a usual interference source, letting another station get through. Similarly, there may also be duct-like openings occurring at sunrise or sunset which can result in stations from particular geographic areas coming through where they are normally not heard. Finally, remember that few stations actually "throw the switch" at exactly the same time. Very often you can hear three or more different stations on the same frequency with the same listed sunrise or sunset time making their changes one after another.
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