By Tomas Hood, NW7US
It is that time of year, again, when propagation gets a bit tricky. Conditions up in the ionosphere can vary drastically from one day to the next. One day, typical summertime conditions rule, while the next we may well see conditions resembling those typical of autumn. This is the month where we see less and less summer-like conditions, and improvements signaling the arrival of the autumn DX season.
Autumn DX conditions feature somewhat higher daytime usable frequencies and somewhat lower nighttime usable frequencies. When you add equinoctial conditions that can begin as early as late August, we often experience optimum openings between the northern and southern hemispheres on the one hand, but periods of active to stormy conditions on the other.
Despite Solar Cycle 24’s low to moderate activity level, during the daylight hours good DX conditions should be possible on 17 and 20 meters. Expect signals on these bands to peak approximately during the two-hour window immediately following sunrise and again during the late afternoon. These two bands will see openings for DX throughout the daylight hours. Fairly good DX openings should occur along an arc extending across central Africa, Latin America, and into the far Pacific area. Peak conditions should occur during the afternoon hours, but an increasing number of earlier openings should be possible by early September.
Between sundown and sunrise 20 meters is expected to be the best DX band. Openings might be possible to many areas of the world, some with surprisingly strong signal levels, especially when using digital and CW modes. Until good DX conditions should be found for openings toward Latin America, the far Pacific, and into Asia. You might even catch some activity on 17 or even 15. Fairly good conditions are also expected on 30, 40, 60, and 80 meters despite the high static level at times. Openings should be possible before along an arc extending from northern Europe, through Africa, and into Latin America, the far Pacific, and Asia after .
By late August it should be possible to work some DX on 160 meters during the hours of darkness. Conditions on this band, as well as on 40, 60 and 80 meters, will tend to peak just as the sun begins to rise on the light, or easternmost, terminal of a path.
For short-skip openings during August and early September, try 80 meters during the day for distances less than 250 miles, with 60 and 40 meters also usable. During the hours of darkness both 80 and 160 meters should provide excellent communications over this distance. For openings between 250 and 750 miles use 30 and 40 meters during the day for distances up to 500 miles, and 20 and 17 meters between 500 and 750 miles. At night, 40 and 30 meters should be the best bands for this distance until , with 80 meters optimum from to sunrise. Try 60 meters, as well. For openings between 750 and 1300 miles, try 20 and 17 meters, as they should provide optimum propagation during the hours of daylight. Optimum conditions should continue on these bands for this distance range after sundown and until . Between and sunrise the best band should be 40 meters, but check 60 meters, too. For openings between 1300 miles and the one-hop short-skip limit of approximately 2300 miles try 20 and 17 meters during the day, with 15 meters also usable. After sundown try 30, 40 and 60 meters, with 80 meters also providing good propagation conditions for this distance range.
Sporadic-E propagation usually begins to taper off during August, but it should continue to occur fairly frequently. Some 6-Meter sporadic-E openings are expected during the month over distances of approximately 750 to 1300 miles. During periods of intense and widespread sporadic-E ionization, two-hop openings may be possible considerably beyond this range. Also check the 2-Meter band for an occasional sporadic-E short-skip opening between approximately 1200 to 1400 miles. While sporadic-E short-skip openings may occur at any time, there is a tendency for them to peak between 8 AM and noon, and again between local daylight time.
The Perseids meteor shower covers the period of late July to late August. The peak is expected to occur mid-August and will be most observable in the Northern Hemisphere. The maximum hourly visual rate could reach 100.
Aurora? Check for aurora-scatter type openings, on both 6 and 2 meters, which can range from a few hundred up to about a thousand miles, and they are usually characterized by very rapid flutter and Doppler shift on SSB signals. These aurora events may occur when the K-index numbers rise above 5.
For the very patient, check the six meter band for possible trans-equatorial (TE) openings between local daylight time. This type of propagation favors openings from the southern tier states into South America, with the signal path crossing the magnetic equator at a right angle. TE openings during August are rare, but they can occur. Very weak signals and severe flutter fading usually characterize them.