Summer approaches. Daytime MUF's are declining due to the heating and thinning of the ionosphere. Up to now, this has not adversely effected DX propagation. Late spring also brings us high MUF's at night. This is the time of year when daytime and nighttime MUF's approach each other and open paths which span areas of both day and night. This is especially noticeable at the peak of the solar cycle, when 15 Meters opens for worldwide propagation almost 24 hours a day.
We are still early in the cycle, but should look for unusual openings on the high bands because this is the season for them. With fluxes usually around 100, signals on 15 are still sparse. There are openings to Asia well after dark, and occasional signals from Europe in the afternoon. The east/west paths are fine, with VK/ZL coming through strong in the evening. Things will be much different with the flux goes above 150 - maybe next year.
17 Meters is more interesting. We are finding many of the same openings as on 20. Well into the evening we find polar openings and European sigs, along with the expected openings to the Pacific. Asian paths are open in the morning, including the high latitude path to southeast Asia. All these windows open on 15 at sunspot peaks, and 17 will also be much improved.
The thinning ionosphere is already effecting 10 & 12 Meters, which don't get much attention during the summer months. Daypath MUF's are at their lowest in July, which is a month of rapid deterioration for 15 Meter propagation. For now, we can enjoy the occasional nightpath signals on this band through June.
20 is open well past midnight nowadays. The path to Russia and Siberia is open through the evening, though ham radio activity in the CIS has dropped in recent years. The band just doesn't sound as busy anymore. The 20 Meter opening swings to Europe later in the evening as sunrise sweeps over that continent. This DX is workable well past midnight. In the morning 20 brings us awesome conditions to Asia - all of it. Westerly long path should also be watched in the morning. Most of this activity will be from South Africa.
High QRN levels have brought an end to most activity on 40 Meters and lower. The overheated ionosphere will soon be effecting all bands 15 and up. This leaves 17 and 20 Meters for most summer DX work.
Sporadic E season is with us now, bringing short skip to 6 & 10. Operation on 10 SSB requires an account with the 10-10 organization. The novices will tell you all about it if you don't have one. There is a fee, and I have often wondered if this was legal.