In my quest of learning electronics, I try to understand radio propagation. All of the numbers, terminology, and charts can be somewhat overwhelming. Is there a simple, quick reference to better understand the HF progation numbers?

1. K-Index — 0-9. Overall, low is better. Some VHF operators like to see an increasing K Index, because aurora is possible at Kp Index values of 3 and greater. [ARRL, Here comes the sun.]

“Geomagnetic storms, indicated by a Kp of 5 or higher, have no direct effect on propagation. However they disturb the F-layer of the ionosphere, especially at middle and high geographical latitudes, causing a so called ionospheric storm which degrades radio propagation.” [Wikipedia, K-index.]

2. A Index —  1-400; low is better. [IW5EDI, understanding the propagation numbers.]

“The A-index provides a daily average level for geomagnetic activity. Because of the non-linear relationship of the K-scale to magnetometer fluctuations, it is not meaningful to take averages of a set of K indices. What is done instead is to convert each K back into a linear scale called the equivalent three hourly range a-index.”

3. Solar Flux Index — 60 to 300. High is always optimum, this means 100 or better is best. The higher is better for the upper bands especially.

“Solar flux is a measurement of the intensity of solar radio emissions at a frequency of 2800 MHz made using a radio telescope located in Dominion Radio Astrophysical Observatory, Penticton, British Columbia, Canada. Known also as the 10.7 cm flux (the wavelength of the radio signals at 2800 MHz), this solar radio emission has been shown to be proportional to sunspot activity.” [Wikipedia, Ionosphere- Solar Flux.]

4. X-Ray — (integrated into the K-Index) but this value is what determines the severity of the absorption of HF radio signals. The class range is from A/B, C, M and X. Large X-Class solar flares are the least desirable. [RadioReference.com, HF Propagation Quick Reference, by NickCarr.]

“Usually, the bad HF conditions will generally mean improved VHF conditions from 6m to 2m because the ionosphere is in an excited state. This is why 11m (CB) and 10m (HAM) will become very active during these bad HF periods.”

5. Sunspot number (SN) — The sunspot number should be over 100 if we expect the upper bands to open up all day to some part of the world.

6. WWV propagation report — Government frequency and time signals on 2.5, 5, 10, 15 and 20 MHz. “At :18 past, a special geophysical alert report from NOAA is transmitted, containing information on solar activity and shortwave radio propagation conditions. These particular alerts were to be discontinued on September 6, 2011. However, as of June 17, 2011, WWV is announcing at :18 past that the decision has been retracted and that the geophysical alert reports will continue for the forseeable future.” [WWV, Other voice announcements.]

7. Solar-Terrestial Data — Important solar data is presented and you can add it to your website! [N0NBH, Paul.]