FAI occurs on 50 and 144 MHz, usually directly after Sporadic-E events. FAI may appear on 144 MHz even thoguh the Sporadic E MUF did not reach much above 50 MHz. FAI may persist for several hours once it starts. Electrons associated with Es become vertically aligned along the Earth's magnetic field lines. This mode has not been widely utilized by amateurs.
Optimum times appear to be 8 pm to midnight. FAI scattering occurs on a skewed path, in other words not in a direct line. Antennas at both ends of a path should be pointed toward a common scattering region (where there is an active or recent Sporadic E reflection point). The best direction should be determined experimentally by turning the antenna for best results. FAI signals are weak and fluttery. Doppler shifts of up to 3 kHz have been reported at times.
During the best times, 100 watts and a single yagi should allow some contacts to be made. Higher power and larger antennas will give better and more consistent results. FAI may exist on 222 MHz. Maximum distances are on the order of 1400 miles, as for other propagation modes occurring at E layer height.
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