By Tomas Hood, NW7US
We are in the time of year when the Northern Hemisphere experiences the longest day of darkness (the Winter Solstice), when the Sun will be at its lowest point in the sky < http://nw7us.us/1z2FIXA >. This marks the peak of the DX window on the shortwave bands, as well as on the medium wave band. With very short daylight periods, the maximum usable frequencies are generally lower across propagation paths over dark areas in the Northern Hemisphere, making for quiet higher shortwave bands. At the same time, shortwave propagation on the mid-shortwave bands, like 31 meters, often is staying active around the clock. Across daylight regions, ionospheric propagation paths exhibit higher MUFs due to the seasonal position of the Earth at this point in its orbit around the Sun.
With short daylight days, the openings on many paths are short, though possibly strong, on the higher HF frequencies. In general, paths on 31 through 19 meters are now in their seasonal peak, especially between North America and Europe in the morning, and between North America and Asia during the late afternoon hours. 19 and 22 meters are probably the best daytime DX band, opening for DX just before sunrise and remaining open from all directions through out the day, with a peak in the afternoon. Nighttime conditions will be short and weak, and mostly north/south in orientation since the Southern Hemisphere has long daylight hours.
The best band for around the clock DX will be 31 and 25 meters. Twenty-five meters continues to be an excellent band for medium distance (500 to 1,500 miles) reception during the daylight hours, with longer distancereception (up to 2000 to 3000 miles) should be possible for an hour or two after local sunrise, and again during the late afternoon and early evening. 31 and 40 meters provides medium distance daytime reception ranging between 400 and 1200 miles, and beyond 3000 miles during the hours of darkness until two to three hours after local sunrise.
Look for 75 through 120 meters as stable nighttime bands; you can expect great nighttime DX conditions, especially with the decrease in seasonal noise, and the longer hours. Look for Europe and Africa around sunset until the middle of the night, and then Asia, the Pacific, and the South Pacific as morning approaches. Signals below 120 meters are also greatly improved. Tropical and regional stations are easier to hear, with stronger openings late into night and through early morning hours. For live solar and geophysical images and data, be sure to check out the NW7US space weather and radio resource page at < http://SunSpotWatch.com >