In
television, the basic problem is to devise a system by which one can transmit
both sound and picture and receive them over long distances. The technique for
transmission of sound is rather simple. Sound waves are mechanical waves
produced in the air by vibrating elements like reeds in the voice base of the
speaker, or vibrating diaphragms, strings, etc, and are sensed by ears as audio
signals varying with respect to time in the frequency range of 20 to 20,000Hz.
television, the basic problem is to devise a system by which one can transmit
both sound and picture and receive them over long distances. The technique for
transmission of sound is rather simple. Sound waves are mechanical waves
produced in the air by vibrating elements like reeds in the voice base of the
speaker, or vibrating diaphragms, strings, etc, and are sensed by ears as audio
signals varying with respect to time in the frequency range of 20 to 20,000Hz.
For
transmission of sound over long distances, the sound waves are converted with
the aid of a microphone into electrical signals so that they can be sent over
wires as in a telephone. If these audio signals are translated into radio
frequencies by modulation, they can be radiated into space by feeding the RF
energy to suitable aerials. At the receiver, the RF signal is amplified and the
low frequency audio signals are separated by demodulation. These are further
amplified to drive a sound reproducing device like a loudspeaker, which
converts them back to sound.
transmission of sound over long distances, the sound waves are converted with
the aid of a microphone into electrical signals so that they can be sent over
wires as in a telephone. If these audio signals are translated into radio
frequencies by modulation, they can be radiated into space by feeding the RF
energy to suitable aerials. At the receiver, the RF signal is amplified and the
low frequency audio signals are separated by demodulation. These are further
amplified to drive a sound reproducing device like a loudspeaker, which
converts them back to sound.
Transmitting
a picture by converting it into electrical signals is not so simple because the
picture has both space and time variations of brightness information contained
in it. It has a different optical brightness at each different point in it, and
this goes on varying with respect to time in live scenes or in movies. The
human eye can sense all the elements of the picture projected on its retina
with the aid of the many cone and rod sensors and the optical nerves
communicating with the brain. Simultaneous transmission of the brightness
information existing all over the points in the picture and receiving it on an
equal number of point light sources is very different, practically impossible.
Such a parallel television system would require as many sensors to sense
brightness levels at the various points and send the information in parallel to
the reproducing elements, via as many electrical wires or channels. In order to
simplify the process, the sequential ‘scanning’ technique is used to convert
the picture information into single value function of time. This makes it
possible to transmit the picture information over a single pair of wires
serving a channel.
a picture by converting it into electrical signals is not so simple because the
picture has both space and time variations of brightness information contained
in it. It has a different optical brightness at each different point in it, and
this goes on varying with respect to time in live scenes or in movies. The
human eye can sense all the elements of the picture projected on its retina
with the aid of the many cone and rod sensors and the optical nerves
communicating with the brain. Simultaneous transmission of the brightness
information existing all over the points in the picture and receiving it on an
equal number of point light sources is very different, practically impossible.
Such a parallel television system would require as many sensors to sense
brightness levels at the various points and send the information in parallel to
the reproducing elements, via as many electrical wires or channels. In order to
simplify the process, the sequential ‘scanning’ technique is used to convert
the picture information into single value function of time. This makes it
possible to transmit the picture information over a single pair of wires
serving a channel.
