160 Meter ( 1850 kHz )
During the day, ground wave communications over distances of less than 150 km benefit from reliable propagation; at the same time, the strong absorption of the D layer makes communications over greater distances very difficult. At night, when the D layer disappears, the waves can reach the F layer and be reflected. Greater distances are then possible. Atmospheric noise can be very significant and make communications very difficult. Mid-latitude thunderstorms generate a great deal of static, particularly in summer. Best propagation WINTER nights.
80 Meter ( 3500 kHz )
The daytime absorption of the D layer, while less significant than on the 160-meter band, practically closes off this daytime band; however, it remains possible to make contacts up to 400 km using a high angle. As soon as the sun begins to set, intercontinental contacts (as far as the antipodes) become possible. As with the 160-meter band, atmospheric noise is very noticeable and static signals are very important in summer. Best propagation WINTER evenings and nights.
40 Meter ( 7 MHz )
The absorption of the D layer is much lower than on the lower bands, resulting in a near-permanent open signal depending on the propagation mode. During the day, the use of the E layer allows for communications with a range of approximately 800 km under very stable conditions. At night, as soon as ionization begins to decrease, the F2 layer enables highly reliable global contacts. Atmospheric noise is minimal, and static levels, even in summer, are generally lower than signal levels. Best propagation evenings and nights in all seasons.
30 Meter ( 10 MHz )
This band shares characteristics with both the lower (nighttime) and upper (daytime) bands. Atmospheric noise is minimal, and static levels, even in summer, are generally lower than signal levels. During the day, D-layer absorption is negligible, making contacts possible over distances of up to 3000 km. At night, communications with the antipodes are possible. 24/7 use of the F2 layer is feasible. The MUF (Multi-Uniform Frequency) in certain areas may decrease below this frequency. The 30-meter band is the least affected by solar cycles. DX communications on this band are therefore consistently very stable. Best propagation at night in all seasons.
20 Meter ( 14 MHz )
The band is favored by most radio amateurs for global communications. Dependent on the solar cycle, this band is always open for at least a few hours a day for DX traffic via the F2 layer. Short-distance contacts via the E layer are also occasionally possible. During solar maxima, the band can even remain open 24/7. In winter, the band closes relatively early. Atmospheric noise is negligible, even during the day. Best propagation summer days.
17 Meter ( 18 MHz )
This band behaves like the 20-meter band, but it is more sensitive to variations in the solar cycle (11 years). During periods of low solar activity, the 17-meter band is only open to DX during the day along a north-south axis and at latitudes below 50 degrees. During periods of maximum solar activity, the band is open to long-distance communications all day, into the early evening, and even late into the night. Atmospheric noise is negligible, even during the day.
15 Meter ( 21 Mhz )
This band behaves much like the 17-meter band, except that during periods of low solar activity, it can remain completely closed. Highly dependent on ionization, the 15-meter band is only active during daylight hours, particularly during periods of low solar activity. Traffic is very heavy via the F2 layer and very low, but possible, in the ES (sporadic E) band.
12 Meter and 10 Meter ( 25 and 25 MHz
12 This band benefits from the advantages of the 15-meter and 10-meter bands. It is primarily a daytime band during periods of low or moderate solar activity. During periods of high solar activity, the 12-meter band may remain open even at night. During periods of low solar activity, the 12-meter band is only open to DXing during the day along a north-south axis and at latitudes below 50 degrees; however, during these same periods, the band may remain closed all day. From the 12-meter band onward, ES contacts begin to be possible. ES openings are sometimes observable in winter, but their peak occurs between late spring and summer.
11 This band is very sensitive to variations in the solar cycle and therefore highly variable. It benefits from a large number of propagation modes. During periods of high solar activity, the band opens at sunrise and closes a few hours after sunset. During these periods, a power of just a few watts allows contacts over several thousand kilometers. During periods of moderate activity, the band remains open only for transequatorial communications at low latitudes. During periods of minimum activity, DX communications are completely impossible. ES propagation becomes significant on the 10-meter band. It allows contacts over a distance of approximately 5,000 kilometers. It reaches its maximum between May and August.
Solar cycle
https://en.wikipedia.org/wiki/Solar_cycle
2024 was the best propagation on SW, 2026, 2027 and 2028 will be good also but not like 2024 !
- Notes on Solar cycle 25
- The maximum SSN of 160.9 for October 2024 is 73% above the maximum SSN predicted by Zharkova for SC25.
- SILSO has announced October 2024 as the peak of the cycle. It says: "For the coming years, another maximum remains a possibility, but it is unlikely it will be higher than the one in October last year because the Sun has completed its polar field reversal in 2023, and because the ongoing solar cycle is already 5.5 years in progress."
Sporadic E
Sporadic E clouds form at an altitude of approximately 100 kilometers, slightly above the E layer, and are thought to be caused by wind shear generated by high-speed, opposing-direction particle winds. The resulting layer is very thin and highly unstable. It can last from a few minutes to a few hours. These clouds allow for ionospheric reflection at frequencies exceeding 100 MHz. They significantly increase the range of VHF transmitting stations. Unfortunately, the occurrence of sporadic E clouds is not yet predictable, but numerous studies in this area are already revealing interesting details about the regularity and frequency of their occurrence throughout the seasons. The influence of sporadic E clouds is already noticeable on the 10-meter band, very significant on the 6-meter band, and rarer and shorter-lived on the 2-meter band. The best sporadic easterly conditions occur in the Northern Hemisphere during summer, between 06:00 and 18:00, with some possibilities still occurring between 18:00 and 22:00. In Europe and the USA, conditions appear less favorable than in East and South Asia, where they can sometimes be active for up to 20% of the day. In winter, the best conditions are between 11:00 and 18:00, but the frequency of sporadic easterly cloud formation is 80% lower than in summer. A good sporadic easterly break allows for contact over a distance exceeding 2500 kilometers.
Shortwave
https://en.wikipedia.org/wiki/High_frequency
Shortwave broadcasting
Shortwave (also known as High frequency (HF)) transmissions range from approximately 2.3 to 26.1 MHz, divided into 14 broadcast bands. Shortwave broadcasts generally use a narrow 5 kHz channel spacing. Shortwave is used by audio services intended to be heard at great distances from the transmitting station. The long range of shortwave broadcasts comes at the expense of lower audio fidelity.
Most broadcast services use AM transmissions, although some use a modified version of AM such as Single-sideband modulation (SSB) or an AM-compatible version of SSB such as "SSB with carrier reinserted".
Medium wave
https://en.wikipedia.org/wiki/MW_DX
https://mwcircle.org/introduction-to-long-distance-medium-wave-listening/
Shortwave listening
https://en.wikipedia.org/wiki/Shortwave_listening
Propagation for amateur radio operators or SWL
https://webkiwisdrswl.blogspot.com/2025/04/propagation-for-amateur-radio-operators.html
Shortwave bands
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