Good knowledge of the propagation of radio waves and procedures when making connections are very important. The weather is an important factor. Here is some more information about propagation and the sunspot cycle prediction.
There are a number of layers in the ionosphere. Two, there are important: the lower-layer D, which mainly absorbs the low frequencies, and F, the outer-layer, which can bend to the higher frequencies back to the earth.See the right figure.
The effect of both layers depends on the ionization rate, which is the biggest in full sunlight and can be increased even further by sunspots. In darkness, the D-layer in the absence of sunlight does not exist allowing low frequencies to reach the F layer and return to earth. In darkness, the F-layer is still present thinly and allow it to fail result for frequencies above about 12 MHz.
Due to the sunlit cleaves the F-layer is located in the second thick-F layers and then the MUF is much higher, around 28 MHz. Exceptions to the rule are frequent, with the study of the propagation phenomena can fill a lifetime. With regard to the HF-propagation is the ability to apply to the table below is sufficient.
In brief; Without conditions can even come with one kilowatt nowhere. With conditions you at the right time and at the right frequency span great distances, even with small capacities! Many amateurs underestimate the importance of the conditions.
A-index: The degree of distortion of the earth’s magnetic field is measured over the last 24 hours. The index can range from 0 to 150. The lower the index, the better the signal strength on the HF bands.
K-index: The degree of distortion of the earth’s magnetic field is measured over the last 3 hours. This gives a better picture of the interference on the HF bands. The index runs from 0 to 9. The lower the index (1-2), the better are the signals on the RF bands. Greater than 4 is an indication that the tires are not really open.
SFI index : Solar Flux Index, indicates the degree of ionization of the ionosphere on. We’d love to have a high-value SFI.
SSN: Smoothed Sunspot Number, the sunspots number which is dependent on the date. The cycle relating to the SSN is approximately 11 years. At a low SSN, the conditions are moderate, optimally at a high SSN are the conditions. It is expected to achieve the highest SSN value in 2012-2013 to take off again after a 11-year cycle.
In summary: we can expect good conditions at a high SFI, high SSN and lowest possible K-index.