When we talk about HF propagation, we often use the numbers for SFI (Solar Flux Index), K-Factor, A-Factor.
The solar flux index is an indicator for the amount of ionization in the F2 region of the atmosphere. This in turn, indicates the electron concentration. Low electron concentrations indicate poor conditions for long-distance communication, while high concentrations indicate good conditions.
The SFI is a unit of measurement for the amount of Solar Flux or Noise that is emitted at 2800 Hz. These numbers are averages based over the duration of a month. An operator can use these numbers to get an idea for how “Open” the bands are, or how good the HF propagation is.
The SFI can range from below 50 to above 300. A number below 70 is considered bad, and a number around 80 is considered good. A number around 90 is considered better, and a number above 100 is considered best.
The K-Factor is a number representing the magnetic activity as compared to a “quiet” day. This number is made using numbers from various locations. The range for the K-Factor is 0 to 9. The lower the number the better.
K = 0 Inactive
K = 1 Very quiet
K = 2 Quiet
K = 3 Unsettled
K = 4 Active
K = 5 Minor storm
K = 6 Major storm
K = 7 Severe storm
K = 8 Very severe storm
K = 9 Extremely severe storm
The A-Factor is a number that corresponds to the geomagnetic stability and is calculated from the K-Factors from previous days. The lower the number the better.
A = 0 – 7 Quiet
A = 8 – 15 Unsettled
A = 16 – 29 Active
A = 30 – 49 Minor storm
A = 50 – 99 Major storm
A = 100 – 400 Severe storm
These are some examples.
A<=11, K<=3, SFI>=90 then Propagation is OK
A=11, K=2, SFI=245 then Propagation is considered Pretty Good
OK, what if the numbers are not good? That does not mean that you can’t make contacts. This is just some information that an operator can use to get a feel for what propagation might be expected. K values greater than 6 are indicative of a severe solar storm and may indicate that radio blackouts may occur.
In summary, Remember [ Low A, Low K, High SFI ] = Good
Now, Get out there and make some contacts. 73, and see on the Air.