Page 118 - Intro to Space Sciences Spacecraft Applications

105
Communications
This chapter concerns electromagnetic amplitude and phase as well as
frequencies and wavelengths. Amplitude represents the amount of energy
or power the wave contains, and phase indicates where along the wave
form we are at any particular time (in degrees or radians as shown).
As we will see in this section, electromagnetic waves are used for com-
munication purposes to carry information between locations. Before
describing this process, however, some additional information on electro-
magnetic propagation must be presented. These properties and phenome-
na also apply to remote sensing and satellite navigation, discussed later.

Radio Wave Propagation

The electromagnetic spectrum was described in the last chapter in terms
of different bands of frequencies with certain properties. The portions of
the spectrum we will be concerned with here are the radio and microwave
bands which are most commonly used for communication purposes. Fig-
ure 5-2 shows the frequencies associated with these two bands and also
shows how these frequencies have been further subdivided into bands

z RADIO BANDS

wavelength 1M)o m LOO m 10 m 1 m 10 cm I cm 1 mm 1 CLm
MICROWAVE BANDS

wavelength 1 10 cm lcm lmm
Figure 5-2. Communication bands. Certain frequencies have been
designated for particular communications uses.