Рубрика:
25
As we have already mentioned that the science of radio is centered
round electromagnetic fields or waves. In fact, the term “radio” has
been driven from “radiation” – the process of propagating or sending
the waves into space.
The basic elements of any system of radio communication are: a
transmitter and a receiver, a transmitting and a receiving antenna, a
modulator, a cathode-ray tube, a relay, headphones, a loudspeaker, etc.
Text 2 (B). Radio Waves
Radio waves are electromagnetic waves used for radio-
communication. According to their frequencies electromagnetic waves
produce different effects and are generated and detected by different
methods. The waves of highest frequency so far discovered are cosmic
rays, which appear in interstellar space and reach the earth from all
directions. Next in order down the frequency spectrum come X-rays,
ultra-violet rays and ordinary light space, to be followed by infrared
rays and radio waves. The frequencies of radio waves are too low to
be perceived
1
by the eye, although they are of exactly the same type as
light waves, which operate on higher frequencies. Because of their
low frequency, radio waves have to be collected on an aerial system
and made perceptible by converting them to sound or vision. They
have a great advantage over other forms of communication in that
they follow the curvatures
2
of the earth and so are suitable
3
for
communication over great distances.
NOTES:
1
to perceive – воспринимать;
2
curvature – искривление;
3
suitable – подходящий, соответствующий
Text 2 (C). Basic Receivers and Transmitters
A much simplified transmitter block-diagram is shown in fig. 1. This
could be called the all-purpose block-diagram since it could be easily
converted to a low-level or high-level amplitude modulation transmitter, a
single sideband transmitter, or a frequency modulation transmitter. Obviously
in the example, the circuit details would vary greatly, particularly in the
modulators, and if detailed block diagrams were drawn the underlying
similarities in structure would be less obvious.
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