SFI

17 Jun SFI

SFI is an acronym for Solar Flux Index. Solar flux is measured in solar flux units (SFUs). It is the amount of radio noise or flux emitted at a frequency of 2800 MHz (10.7 cm, hence is it also called the 10.7 cm flux index). Solar flux is proportional to propagation. SFI between 100-150: propagation will tend to be good. >150: propagation will tend to be ideal. High SFI values have almost no influence on 30m,40m,80m and 160m bands. SFI value over 150 indicates ideal HF propagation conditions and people with small HF installations can begin exploiting these conditions.

The figure for the solar flux can vary from as low as 50 or so to as high as 300. Low values indicate that the maximum useable frequency will be low and overall conditions will not be very good, particularly on the higher HF bands. Conversely, high values generally indicate there is sufficient ionization to support long-distance communication at higher than-normal frequencies. However,  emember that it takes a few days of high values for conditions to improve. Typically values in excess of 200 will be measured during the peak of a sunspot cycle with high values of up to 300 being experienced for shorter periods.