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Lesson#15
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TELEGRAPH DOES MIRACLE IN DISTANCE
COMMUNICATION
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TELEGRAPH DOES MIRACLE IN DISTANCE COMMUNICATION
TELEX AND TELEPHONE ENTHRALL PRINT COMMUNICATION
It was undoubtedly a historic day when scientist Samuel Morse on
May 14, 1844 successfully established a
link between Baltimore and Washington DC by transmitting the
first tele message ‘What hath God wrought’
on a device invented by him and which we know as telegraph
today.
By this date, it was almost 150 years that print media was
active but was not finding way to reach to a large
audience in a short time. There were no rails and motorcars.
Transport system was as fast as fresh horses
could maintain it. In rains and harsh weathers communication was
blocked.
The news of sending message by wire to a reasonable distance in
real time was received with great warmth
by the print industry across the world which was assessing a
bright future for it was not possible to reach
larger number of people and at a distance not possible to cover
before.
How telegraph system came about?
Fires, smoke signals, and drums have been used since antiquity
to transmit messages over long
distances. The term
telegraph
was coined by scientist Claude Chappe to describe
such methods, a version of
which was invented by him and his brothers to signal each other
while in school. In 1793 Chappe
introduced in France a form of this system for the transmission
of messages based on stations with towers
using a code to transmit signals by the position of crossed
arms.
The idea of the electric telegraph was born when the first
experimenters with electricity noticed that electric
charges could travel through wires over distances. In 1753 in
Scotland Charles Morrison described a system
of 26 wires for transmitting the 26 letters of the alphabet.
Electrostatic charges traveling through these wires
deflected suspended balls at the receiving station. However,
this was never developed as a practical system.
During the early 19th century, several scientists experimented
with the transmission of messages through
electric wires. At this time scientists had gained access to a
steady, low-voltage source of electricity. Karl
Friedrich Gauss and Wilhelm Weber transmitted signals over wires
and detected them with sensitive
galvanometers around 1833. In England Charles Wheatstone
developed a telegraph with a five-needle
galvanometer that indicated the transmitted letters. The
Wheatstone telegraph actually came into use,
linking Liverpool with Manchester in 1839. In Germany Carl
Steinheil developed a telegraph that printed
coded messages on a ribbon.
The electromagnet, a magnet whose field appears when current is
on and disappears when it is off, was
discovered in the 1820s. The American painter Samuel Morse first
became acquainted with an
electromagnet when it was shown to him by a young chemist he met
on a transatlantic ship. Morse realized
that a magnet turning on and off by transmission of a current
from a distant source could be used to send
messages. He soon enlisted America's greatest scientist of the
time, Joseph Henry, to develop ways to cause
an electromagnet to work at a distance. The electric telegraph
became truly functional with the idea of using
a code of dots and dashes to transmit the letters of the
alphabet. Despite this technical help, Morse is given
credit for the invention because he put together a practical
system and got people to accept it.
Morse patented his telegraph in 1837 and officially inaugurated
a link between Baltimore, Maryland, and
Washington, DC, on May 14, 1844, by transmitting the message
"What hath God wrought." The message
was transmitted by a telegraph key, a special switch that allows
an electric current to be rapidly switched in
and out; it was printed in the dot-dash code on ribbons of
paper.
Morse's telegraph quickly spread in the United States, and later
it superseded the existing systems of
Wheatstone and Steinheil in Europe. In 1862, 240,000 km (150,000
mi) of telegraph cable covered the
world, of which 77,000 km (48,000 mi) were in the United States
and 24,000 km (15,000 mi) in Great
Britain. Europe and the United States became linked by an
underwater telegraph cable in 1866.
All rapid long-distance communication within private and public
sectors depended on the telegraph
throughout the remainder of the nineteenth century. Applications
were many: Railroads used the Morse
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telegraph to aid in the efficiency and safety of railroad
operations, the Associated Press to dispatch news,
industry for the transmission of information about stocks and
commodities, and the general public to send
messages. The telegraph's military value was demonstrated during
the Civil War (1861–1865) as a way to
control troop deployment and intelligence. However, the rival
technologies of the telephone and radio
would soon replace the telegraph as a primary source of
communication.
Days of the Morse Code
Data was transmitted at about four to
six bits per second in the latter half of the
1800s, which was as fast as a human hand could
tap out Morse code. The unit on the right is the
telegraph key. A metal bar on the receiver (left)
simply banged against another bar when the
current passed through, creating a clicking
sound.
The print medium was still enjoying from the
facility of telegraph that another great facility was made
available to it as the period of industrial growth got
into top gear in the 19th
century. The new invention was telephone –
a point to point messaging facility by
spoken words. The information conveying system by reporters of
the print media and talking to men-inpower
for obtaining information and passing on to millions others the
next day seemed as a dream come
true.
Telephone in historic perspective
Throughout history, people have devised methods for
communicating over long distances. The
earliest methods involved crude systems such as drum beating or
smoke signaling. These systems evolved
into optical telegraphy and by the early 1800s, electric
telegraphy. The first simple telephones, which were
comprised of a long string and two cans, were known in the early
eighteenth century.
A working electrical voice-transmission system was first
demonstrated by Johann Philipp Reis in 1863. His
machine consisted of a vibrating membrane that opened or closed
an electric circuit. While Reis only used
his machine to demonstrate the nature of sound, other inventors
tried to find more practical applications of
this technology. They were found by Alexander Graham Bell in
1876 when he was awarded a patent for the
first operational telephone. This invention proved to
revolutionize the way people communicate throughout
the world.
Bell's interest in telephony was primarily derived from his
background in vocal physiology and his speech
instruction to the deaf. His breakthrough experiment occurred on
June 2, 1875. He and his assistant,
Thomas Watson, were working on a harmonic telegraph. When a reed
stuck on Watson's transmitter an
intermittent current was converted to a continuous current. Bell
was able to hear the sound on his receiver
confirming his belief that sound could be transmitted and
reconverted through an electric wire by using a
continuous electric current.
The original telephone design that Bell patented was much
different than the phone we know today. In a
real sense, it was just a modified version of a telegraph. The
primary difference was that it could transmit
true sound. Bell continued to improve upon his design. After two
years, he created a magnetic telephone
which was the precursor to modern phones. This design consisted
of a transmitter, receiver, and a magnet.
The transmitter and receiver each contained a diaphragm, which
is a metal disk. During a phone call, the
vibrations of the caller's voice caused the diaphragm in the
transmitter to move. This motion was
transferred along the phone line to the receiver. The receiving
diaphragm began vibrating thereby producing
sound and completing the call.
While the magnetic phone was an important breakthrough, it had
significant drawbacks. For example,
callers had to shout to overcome noise and voice distortions.
Additionally, there was a time lapse in the
transmission which resulted in nearly incoherent conversations.
These problems were eventually solved as
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the telephone underwent numerous design changes. The first
phones made available to consumers used a
single microphone. This required the user to speak into it and
then put it to the ear to listen. Thomas
Edison introduced a model that had a moveable listening earpiece
and stationary speaking tube. When
placing a call, the receiver was lifted and the user was
connected directly to an operator who would then
switch wires manually to transmit. In 1878, the first manual
telephone exchange was opened. It served 21
customers in New Haven, Connecticut. Use of the telephone spread
rapidly and in 1891, the first automatic
number calling mechanism was introduced.
Long-distance service was first made available in 1881. However,
the transmission rates were not good and
it was difficult to hear. In 1900, two workers at Bell System
designed loading coils that could minimize
distortions. In 1912, the vacuum tube was adapted to the phone
as an amplifier. This made it possible to
have a transcontinental phone line, first demonstrated in 1915.
In 1956, a submarine cable was laid across
the Atlantic to allow transatlantic telephone communication. The
telecommunication industry was
revolutionized in 1962 when orbiting communication satellites
were utilized. In 1980, a fiber-optic system
was introduced, again revolutionizing the industry.
Background
Telephones still operate on the same basic principles that Bell
introduced over one hundred years
ago. If a person wishes to make a call, they pick up the
handset. This causes the phone to be connected to a
routing network. When the numbers are pressed on a touch-tone
keypad, signals are sent down the phone
line to the routing station. Here, each digit is recognized as a
combination of tone frequencies. The specific
number combination causes a signal to be sent to another phone
causing it to ring. When that phone is
picked up, a connection between the two phones is initiated.
The mouthpiece acts as a microphone. Sound waves from the user's
voice cause a thin, plastic disk inside
the phone to vibrate. This changes the distance between the
plastic disk and another metal disk. The
intensity of an electric field between the two disks is changed
as a result and a varying electric current is sent
down the phone line. The receiver on the other phone picks up
this current. As it enters the receiver, it
passes through a set of electromagnets. These magnets cause a
metal diaphragm to vibrate. This vibration
reproduces the voice that initiated the current. An amplifier in
the receiver makes it easier to hear. When
one of the phones is hung up the electric current is broken,
causing all of the routing connections to be
released.
The system of transmission presented describes what happens
during a local call. It varies slightly for other
types of calls such as long distance or cellular. Long distance
calls are not always connected directly through
wires. In some cases, the signal is converted to a satellite
dish signal and transmitted via a satellite. For
cellular phones, the signal is sent to a cellular antenna. Here,
it is sent via radio waves to the appropriate cell
phone.
With the combination of telegraph and telephone systems,
scientists worked to hand over print media
another great facility in the form of telex
Telex
By 1935, message routing was the last great barrier to full
automation. Large telegraphy providers
began to develop systems that used telephone-like rotary dialing
to connect teletypes. These machines were
called "telex". Telex machines first performed
rotary-telephone-style pulse dialing, and then sent baud dots
code. This "type A" telex routing functionally automated message
routing.
The first wide-coverage telex network was implemented in Germany
during the 1930s. The network was
used to communicate within the government. At the then-blinding
rate of 45.5 bits per second, up to 25
telex channels could share a single long-distance telephone
channel, making telex the least expensive
method of reliable long-distance communication. |
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