Newnes Radio and RF Engineering Pocket Book, 3rd Edition

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both direct and reflected components (see Figure 1.11 ), and is affected

by refraction and diffraction. The importance of these effects varies

with frequency, the nature of the terrain and of objects close to the

direct path, and the type of communication, e.g. data. Apart from

medium-wave broadcasting, space waves are used mainly for com-

munications using frequencies of VHF and upwards.

The range of space waves is the radio horizon. However, places of

little or no signal can arise in the lee of radio obstacles. Fortunately,

they may be filled with either reflected or diffracted signals as depicted

in Figure 1.14.

Tropospheric scatter

The tropospheric, or forward, scatter effect provides reliable, over

the horizon, communication between fixed points