09_02_2011_16_19_57 by xiangpeng

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                                Two - way radio




       Radio broadcasts only go one way, from the station to your radio. You can
listen to radio. But you can't talk back. Two-way radio lets people talk to each
other on radio waves.

      Police officers and fire fighters use two-way radio. Fire fighters at a big
blaze can call for more help on their two-way radios. Soldiers use two-way radios
on battlefields.

       Two-way radios are available in mobile, stationary base and hand-held
portable configurations. Hand-held radios are often called walkie-talkies or handie-
talkies. A push-to-talk or Press to Transmit button is often present to activate the
transmitter.

       A mobile phone or cellular telephone is an example of a two-way radio that
both transmits and receives at the same time (or full-duplex). It uses two different
radio frequencies to carry the two directions of the conversation simultaneously.

                                  About radio days

       Radio Days was born out of an interest in all things Old Time Radio,
education, and an interest in the World Wide Web. It began in early 1995 and was
the first domain specifically dedicated to old time radio. The web site has been
featured in many publications including The New York Times, USA Today, CNN
and many educational institutions.

       The mission of this site is to be both an educational tool as well as a
historical reference for the various aspects of Old Time Radio including drama,
comedy, mystery, and news.
                    How does radio waves get into the air?
      A radio station sends electrical signals through wires to a tall called a
broadcast antenna. Electrical signal get changed into radio waves at the antenna.
The antenna sends the radio waves out in all directions.

       Some radio stations broadcast on AM radio waves. In AM (amplitude
modulation) radio transmissions, the amplitude of the combined audio frequency
and radio frequency waves varies to match the audio signal. AM radio is subject to
problems with static interference. Electromagnetic waves (like radio waves) are
produced by the spark discharges in car ignition systems, brushes of electric
motors and in all sorts of electrical appliances, as well as in thunderstorms. There
is considerable background noise that changes the amplitude of the radio wave
signal adding random crackling noises called static.

      Some programs are broadcast on FM waves, but FM waves make clearer
sounds. In FM (frequency modulation) radio transmissions, the frequency of the
combined waves changes to reproduce the audio signal. For example, higher
frequency is associated with the peak amplitude in the audio wave. FM waves do
not have a problem with interference because the noise background does not
modify the radio wave frequency. In addition FM waves give better sound
reproduction.
                              Plan:

1. About radio days.

2. How do radio waves get into the air?

3. Two-way radio.
             Personal Pronouns: Agreement with collective nouns

The following are examples of collective nouns:
         audience      couple        family              public
         class         crowd         government staff
         committee     faculty       group         team
  a) My family is large. It is composed of nine members. When a collective
      noun refers to a single impersonal unit, a singular pronoun (it, its) is used
      as in (a).
  b) My family is loving and supportive. They are always ready to help me.
      When a collective noun refers to a collection of various individuals, a
      plural pronoun (they, them, their) is used, as in(b).

                             Using Reflexive Pronouns

      The following are reflexive pronouns:
              myself                        ourselves
              yourself                      yourselves
              himself, herself, itself themselves
      a) He looked at himself in the mirror.
         A reflexive pronoun usually refers to the subject of a sentence. In(a): he
         and himself refer to the same person.
      b) He himself answered the phone, not his secretary.
      c) He answered the phone himself.
         Sometimes reflexive pronouns are used for emphasis, as in(b) and (c).
      d) She lives by herself
         The expression by + a reflexive pronoun usually means "alone", as in(d).

								
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