SKIP DISTANCE AND ZONERecall from your previous study that atransmitted radio wave separates into two parts,the sky wave and the ground wave. With thosetwo components in mind, we will now brieflydiscuss skip distance and skip zone.Skip DistanceLook at the relationship between the sky waveskip distance, skip zone, and ground wavecoverage shown in figure 1-8. The skip distance isthe distance from the transmitter to the pointwhere the sky wave first returns to the earth. Theskip distance depends on the wave’s frequency andangle of incidence, and the degree of ionization.Figure 1-8.—Relationship between skipzone, skip distance, and ground wave.Skip ZoneThe skip zoneis a zone of silence between thepoint where the ground wave is too weak forreception and the point where the sky wave is firstreturned to earth. The outer limit of the skip zonevaries considerably, depending on the operatingfrequency, the time of day, the season of the year,sunspot activity, and the direction of transmission.At very-low, low, and medium frequencies, askip zone is never present. However, in the high-frequency spectrum, a skip zone is often present.As the operating frequency is increased, the skipzone widens to a point where the outer limit of theskip zone might be several thousand miles away.At frequencies above a certain maximum, theouter limit of the skip zone disappears completely,and no F-layer propagation is possible.Occasionally, the first sky wave will return toearth within the range of the ground wave. In thiscase, severe fading can result from the phasedifference between the two waves (the sky wavehas a longer path to follow).REFLECTIONReflection occurs when radio waves are“bounced” from a flat surface. There are basicallytwo types of reflection that occur in theatmosphere: earth reflection and ionosphericreflection. Figure 1-9 shows twoFigure 1-9.—Phase shift of reflected radio waves.1-7
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