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Types of Signals |
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Analogue
Signals |
Telephone, radio
broadcast or TV signals are very common types of analogue
signals that are used by general public. They are represented
by voltage wave forms that have different amplitudes
at different instants of time. |
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Telephone Signals: |
Electrical signals for the word THREE |
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TV Picture Signals: |
A T.V signal |
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Radio Broadcast Signals: |
Another very
important analog signal is the radio broadcast signal
used for the education and entertainment of the general
masses. These signals may be in the form of speech or
music. Though the speech signals occupy a bandwidth
of 4 KHz only, the music occupies a considerable large
bandwidth. A high fidelity music programmer occupies
a frequency band that extends from 20 Hz to 16 KHz giving
a bandwidth of 16 KHz approximately. Thus, a high fidelity
(Hi - Fi) music programmer occupies as much channel
and width as is required by four telephone channels.
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Digital
Signals |
Digital signals
comprise of pulses occurring at discrete intervals of
time. The pulse may occur singly at a definite period
of time or as a coded group. These signals play a very
important role in the transmission and reception of
the coded messages. Simplest types of digital signals
are the Telegraph and Tele-printer signals but sometimes
analog messages are also converted into digital form
before being transmitted for certain reasons which are
discussed in a later section. |
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Telegraph Signal: |
Telegraph signal using single current
working |
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Telegraph signal using double current
working |
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Radar Signal: |
Radar is a device
which is used to find out the location of distant objects
in terms of range and bearing. This is done by transmitting
a short period signal and beaming it to the target.
The reflected signal is picked up by the radar receiver
and is used to determine the location of the object.
The radar signal shown in illustration below is basically
a train of rectangular pulses transmitted at a low pulse
repetition frequency (around 1 KHz). The width of the
pulses employed is in the range of 0.1
sec duration. |
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A Radar signal |
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Data
Signals |
Data signals
are required to transmit very important data from one
place to another. Common examples are transmission of
business, industrial and statistical data to a computer
centre for analysis. Another example is transmission
of the data by the satellites to earth stations where
they are analyzed. The data to be transmitted is converted
into pulses. Data signals are therefore in the form
of digital signals and may be analyzed by using Fourier
analysis. The bandwidth required varies from one system
to another but is usually in the range of a few hundred
hertz to a few kilohertz. |
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