Ian Waugh - A Mariner\'s Guide to Marine Communications

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Figure Z6 (not to scale!)

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Energy flows across the earth's surface (ground wave propagation) and up into the

sky - where it is 'refracted' (bent-back) by the 'ionosphere' (sky-wave propagation).

3 4MHz and 2MHz Signals are absorbed by the ionosphere during the

day and are not refracted hack to earth.

4 At night the lower layers of the ionosphere disappear, leaving a single

layer at about 200-250 miles above the earth's surface.

5 The 4MHz, 6MHz, 8MHz and 12MHz bands will achieve much

greater range during night-time conditions than during daytime

152 THE NAUTICAL INSTITUTE