The A index is a linearized scale of the K index. The K index is quasi-logarithmic and measured once every 3 hours. K value is 5 or above constitute an ionospheric storm The higher the A (0 to 400) or K (0-9) value the greater the disturbance (where free electrons are stirred up) are in the F layers which can reduce MUF by up to 50%Ĭoncentrate closer to the Polar regions (i.e. The higher the indices, the worse the HF bands will be. The geomagnetic indices A and K measure the strength of the Earths magnetic field from its baseline (Quiet magnetosphere) level. Real-time critical frequency F2 layer map from IPS (Ionospheric Prediction Service) Too high and it will not be reflected back to Earth. RF signals reflected by the F layer will travel further (~2400 miles), then the closer E layer reflected distance(~1200 miles).Ĩ0m-40m take advantage of the E layer, but are strongly affected by the D layerĢ0m band can take advantage of both E and F layersġ5m-10m band take advantage of the F layerĪlso, Antenna Take off Angle is very important. too high will simply pass through all the layers into outer space. Higher RF frequencies pentrate higher into the E and F layer. Daytime you get a F1 and F2 layer (highest).Īir density is low so RF energy is re-radiated (reflected) rather than absorbed as in the D layer. The F layer is formed by extreme Ultraviolet rays. The Sporadic E layer (intense clouds of electrons) can reflect up to VHF frequencies while the normal E layer works up to ~10 mhz Real-time Global D-Layer Absorption map from NOAA space weatherĮ (above D) and F (highest) layers stay in place day and night. LUF (Lowest Usable Freq) means any Freq below this value will be completely absorbed by the D layer. (longer waves) hit more free electrons which in turn hit more air molecules due to air density at low altitudes.
So for 10m operation during the daytime, its best to have small D layer and a large F layer.ġ60m-40m band during the daytime may be absorbed (in part or all) by the D layer The D layer absorbs RF at the low end (mostly up to 10mhz) of the HF spectrum (high end HF passes through). The air density is high at the D layer, but the free electron density is actually low due to high rate of recombination of electrons. Each layers properties is explained below in the following sections.Ĭhecking Propagation based on current Radio contacts and plotting them on a world map (DXMAPS.COM)Ĭhecking Propagation based on Tropospheric Ducting Forecast ()ĭ (lowest) layer mostly appears with direct Sun (Ultraviolet radiation), but can also occur due to hard X-Ray emissions during a Solar event. But the density of free electrons and their height determine whether RF photons gets absorbed, refelected, or passes through. These free electrons can act as a mirror to the RF photons from your radio waves. The Ionosphere layers responsible for HF Propagation Space Weather - HF Radio Wave Propagation
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