LESSON
4
TELEGRAPH
I. Consider the
following
questions in
the group of
four. A
spokesperson will report
on your discussion
to the
whole group.
1. Why is telegraph still popular now?
2. Are there any private wire systems in
3. What can you say about modern telegraph
services in our country?
II.
Read the text
below and check its
comprehension.
Telegraph
Telegraph is a system of communication
employing electrical apparatus to transmit and receive signals in accordance
with a code of electrical pulses. Originally the term telegraphy referred to
any form of communication over long distances in which messages were
transmitted by signs or sounds.
The Morse Telegraph
The first electrical instruments for
telegraphic transmission were invented in the
While experimenting with his
instrument, Morse found that signals could be transmitted successfully for only
about
Because telegraphy was too expensive for widespread
use,
several means of sending some messages simultaneously over a single
line were developed. In duplex telegraphy, the earliest advance of this kind,
one message can be transmitted simultaneously in each direction between two
stations. In quadruples telegraphy, invented in 1874 by the American engineer
Thomas Edison, two messages were transmitted in each direction simultaneously.
In 1915 multiplex telegraphy came into use, permitting the transmission of
eight or more messages simultaneously. Because of this and the development of
teleprinting machines during the mid-1920s, the Morse manual telegraph system
of code and key was gradually discontinued for commercial use and replaced by
automatic wire and wireless radio-wave methods of transmission.
Automatic Telegraph
Systems
There are two basic systems of
modern telegraphic communication: the teleprinting system (teletype), which is
still in use, and the facsimile repro-duction system, which became obsolete in the
1980s.
Teleprinting
In teleprinting, the message is
received in the form of typed words on a pa-per form. In this system each letter of the
alphabet is represented by one of 31 combinations of five equal-interval electronic impulses, with the sequence of
used and unused intervals determining the
letter.
The start-stop printing code
uses seven pulses for each character,
the first pulse indicating the
begin-ning and the seventh pulse the end of the
letter.
The transmitter or teletypewriter consists of a typewriter like keyboard
and may or may not record the message
on tape before it is transmitted. The recei-ver is basically like a typewriter without
a keyboard that prints the message on
a tape or a paper form. Most machines in the start-stop system are both
transmitters and receivers. News organizations were among the major users of the teletype
and similar communications systems. By
the early 1990s, press
associations and broadcast media transmitted both text and pictures
electronically via satellite.
Facsimile
Reproduction
Facsimile telegraph systems, which send and
receive images and text, have been rendered largely obsolete by facsimile
transmission, commonly referred to as fax.
Telegraph Carrier Media
The electrical impulses that make up telegraph
messages may be carried through wire circuits or may be broadcast as radio
waves.
When Morse invented the telegraph,
the only way that a message could be carried from one point to another was by
wires strung directly from the transmitting device to the receiver, regardless
of the distance. The wire could carry only one message at a time, and
reamplification and signal correction devices had to be set up at regular
points along the line. By utilizing carrier currents, which are alternating
currents of a number of different frequencies, a single pair of wires can
simultaneously transmit hundreds of messages, for each frequency represents a
transmission channel. The various channels are combined at the sending station
into the carrier current transmitted by the telegraph wires. At the receiving
end the carrier current is passed through electrical filters, each of which
transmits only a particular frequency to an appropriate receiving device. Thus,
a great number of individual channels may be obtained with only one electrical
circuit.
Microwave Transmission
The use of microwave radio
transmission for long-distance telegraphic communication all over the world
grew to be of major importance after World War II ended in 1945. The first commercial microwave radio
link in telegraphy began operation between
Microwave telegraphy is capable of carrying vocal, printed, graphic,
photo-graphic, and video communication almost instantaneously and in large
quan-tities. It operates in the
4000-megahertz range of the
commercial communi-cations band. In this range, 40
voice bands are available in either direction, providing about 800 telegraph
channels. The radio signals originating at the broadcast source are relayed to
their destination by a series of parabolic reflector antennas mounted at the
top of tall masts. In order to overcome weakening of the signal by distance and
the curvature of the earth, these microwave relay antennas are placed at
line-of-sight intervals about
Modern Telegraph Services
In the 1950s and 1960s
a variety of public and private telegraphic services
became available from various carriers.
Telex
In
Broadband Exchange Service
This service, introduced in 1964,
provided subscribers
with a choice of high-quality radio channels for the
rapid transmission of data in various forms, for facsimile and other record
communications, and for voice communication. Improvements to the system made it
possible to achieve high-speed transmission between
computers and business machines.
Private
Wire Systems
These
services, used for high-speed exchange of
data, are leased by busi-nesses or government agencies that have
branches in
many
parts of the
world. They operate through digital computer centers by means of punched cards, perforated tape, and magnetic tape. The largest and most advanced of these
systems is the Automatic Digital Data Network (AUTODIN), which serves the U.S.Department of
Defense. The Advanced Record System
(ARS) serves the General Services Administration of
the federal government. Other private
wire systems serve large brokerage
firms and banks.
Computer
Centers
In response to the needs of
subscribers for a variety of communication and information services,
"computer-library" centers have been established to provide exchange
of data and collection of information of every possible type. The computer
centers are available to subscribers through
the Telex system and through normal telephone lines.
Comprehension Check Up
1. Who
invented the first electrical instruments
for telegraphic transmissi-on?
2. How were messages transmitted? 3. How did the original Morse receiver work?
3. What do you know about duplex, quadruplex and multiplex telegraphy? 4. What
are the basic systems of modern telegraphic communication? 5. How may the
electrical impulses be carried? 6. When did the commercial microwave radio
begin operation in telegraphy? 7. How does microwave telegraphy work? 8. When
was microwave transmission established? 9. What can you say about the Telex
system? 10. What did Broadband Exchange service provide subscribers with? 11.
What were private wire systems used for? 12. Why were computer centers
established?
III.
Choose the best answer.
1. The word telegraph refers to …
a) radio-relay system; b) system of
communication; c) pulse-modulation system; d) control system.
2. Duplex
telegraphy implies that…
a) four messages
can be transmitted simultaneously in each
direction bet-ween 2 stations; b) three messages can be transmitted simultaneously in
each direction between 2 stations; c)
two messages can be transmitted
simul-taneously in each direction between 2 stations; d) one
message can be trans-mitted
simultaneously in each direction between 2 stations.
3. The word receiver
defines …
a) equipment that
generates and sends electro-magnetic impulses; b) equip-ment that creates signals; c) equipment that receives signals; d) equipment that converts signals.
4. To transmit messages implies
that one should …
a) send information to smb.; b)
deliver messages; c) send a letter to smb.;
d) dial smb.’s number.
5. Telegraphic communication consists of
…
a) two basic systems: the teleprinting system
(teletype) and the facsimile; b) teletypewriter switching system; c) television
relay system; d) time-division multiplex system.
6. The word transmitter
refers to …
a) equipment that transforms
signals; b) equipment that reflects signals; c) equipment that sends out
signals; d) equipment that modulates signals.
7. The word communication means …
a) the process by which people exchange information; b) data
collection; c) the process of making a telephone call; d) the process of
mastering new technologies.
8. The best explanation of Telex
might be …
a) a triplex system; b) a system of sending
messages from one place to another; c) a system of direct-dial teleprinter exchange; d) an optical commu-nication system.
9. Microwave
telegraphy deals with …
a) scanning process; b) carrying
vocal, printed, graphic, photographic and
video communication almost
instantaneously; c) developing process; d) litho-graphy process.
10.
The best explanation of the Broadband Exchange Service
might be …
a) service which provides subscribers with a
choice of high-quality radio
channels
for the rapid transmission of data in various forms; b) long distance service;
c) broadcasting service; d) public radio communication system.
11. The word teleprinting means that …
a) the message
is received in the form of symbols;
b) the message is recei-ved in the form of codes; c)
the message is received in the form of typed words on a paper form; d) the
message is received in the form of digits.
12.
The best definition of
the Facsimile telegraph systems might be …
a) systems which disseminate information
from public information supplies
into home or office; b) paging systems; c) systems which display still frames
of information from a remote data base on a home TV set screen; d) systems
which send and receive images and texts.
IV.
Use the
right verb from those given below.
to lease, to send, to
deliver, to relay, to operate, to make up, to receive, to print, to record, to
set up, to mount.
V.
Are the following statements True or False?
1. The
first electrical instruments for telegraphic transmission were inven-ted in
VI.
Express the main idea of
each
paragraph
in one sentence.
VII.
Summarize the
text and be ready to retell it.
VIII.
Tell us about
the advantages and disadvantages of
using telegraph.