Radio Telegraph

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Propagation

Sun Spot number
Higher sunspot numbers indicate increased ionizing radiation from the sun which enhances the ionosphere's ability to refract HF signals.  Sunspot numbers can vary from 0-200 during the peak of a 11-year solar cycle.

Solar Flux Index
SFI is a measurement of radio signals from the sun.  The index is taken once a day at a frequency of 2800 MHz(10.7 cm).
 - Increased radio noise from the sun means more ionizing radiation
 - Solar flux values range from 60 (no sunspots) to 300

A Index
A indexes are derived from K indexes but converted to a linear scale in gammas. They can range from 0 to 400 but it is rare to see it go above 75 to 100.  A index readings are normally between 4 and 50.
 - Values below 10 are very desirable for HF communications
 - Values above 10 may indicate excessive absorption of HF radio waves
 - Higher absorption indicates increased storm conditions in the ionosphere

K Index
K indexes reflect geomagnetic conditions (solar particle effects on earth's magnetic field).  Values range from 0 to 9.
 - Lower numbers mean quieter ionosphere
 - When K rises, HF propagation conditions tend to worsen