- Bharat Heavy Electricals Limited provides training on telecommunication systems. It is India's largest engineering firm involved in power and energy sectors. - Telecommunication involves transmission of information over distances using electronic devices like phones, TVs, radios. It works through telephone exchanges and uses various tones and frequencies. - A telephone exchange uses electromechanical or electronic switching systems to connect calls. It provides functions like conferencing, callback, and call transfer through facilities like tones, cables, and the main distribution frame.

1. BHARAT HEAVY ELECTRICALS LIMITED
TRAINING SUMMARY
ON
TELECOMMUNICATION
SYSTEMS
Submitted To : Submitted By:
Ms.Ashita Vermani Mr. Vikrant Negi
ET-K, IV Yr

2. THE ORGANIZATION
• Established more than 50 years ago
• Primarily set up to meet the needs of the power sector in the country.
• Largest engineering enterprise in India.
• Operations cover conversion, transmission, utilization and conservation of
energy in core sectors of the economy like Power, Industry and
Transportation.
•BHEL has 13 manufacturing divisions, 8 service centers and 4 Power
Sector Regional Centers, in addition to over 150 project sites spread all
over India and even abroad.

3. TELECOMMUNICATION
•Telecommunication is the assisted transmission over a distance for the
purpose of communication.
• It involves the use of electronic devices such as telephone, television,
radio or computer

4. BLOCK DIAGRAM OF
TELECOMMUNICATION SYSTEM

5. TELEPHONE EXCHANGE
• Often called Telephone Switch
• First telephone exchange was installed in 1878
• The first switching technology implemented was MANUAL SWITCHING which required
an operator.
• AUTOMATIC SWITCHING was introduced in 1891 and is of two types:-
1. ELECTROMECHANICAL
2. ELECTRONIC

6. 1. Electromechanical switching involved –
STEPPING SWITCH called as the STROWGER SWITHING SYSTEM
• It made use of a four number sequence to connect the call to a neighborhood
• Later on, area codes were created.
2. Electronic switching system
• Stored Program Control
• Made use of computers as central control
• High speed of operation

7. Fig. Electronic Exchange

8. ELECTRONIC EXCHANGES
Electronic Exchanges are of two types:
1.Tone type:
• sine waves are used.
• speed of dialing for a given number is more than that of Pulse type.
• Tone dialing handsets use a numeric keypad
2. Pulse type:
• square wave is used due to which the dialing speed is lesser.
• Pulse dialing handsets usually have rotary dials.

9. TONES USED IN MODERN TELEPHONY
1.Dial Tone :
•When handset is picked up from the cradle, then Dial tone is heard if a free line is
available.
•means that the instrument is ready to send the signals to the exchange.
•This tone is a continuous burble sound of 400 Hz. modulated by 25Hz. and is sent to the
calling subscriber as soon as his line seizes the free line.
• The subscriber must not dial before receiving this tone; otherwise he is liable to get wrong
connection.

10. 2. Busy Tone:
• When the called subscriber is engaged with other call, this tone is heard. It consists of
a sound of 400 Hz. which is regularly interrupted at equal intervals. It is generally on for
0.75 sec. and off for also 0.75 sec.
3. Ringing Tone:
• When a number is dialed then telephone of the called subscriber starts ringing.
• Ringing tone of interrupted 400 Hz. supplies modulated by 25 Hz.
• When this ringing tone is received, the calling subscriber knows that the connection is
completed and that the bell of the called subscriber is ringing.
4. Number Unobtainable Tone:
•This tone is sent when the number dialed cannot be obtained.

11. Powers providing circuits
• Outside the exchange
• Inside the exchange

12. Outside the Exchange:
• The voltage supplied in Indian Subcontinent is 220-volts/50 Hz. A.C. but for the
normal working of the exchange 48(46-53) volts of D.C. is required.
• Hence a Rectifier circuit, backed with battery array for power-failures, is used.
Inside the Exchange:
•Inside the telephone exchange various types of power supplies are used for
powering various modules (for example: - Line-cards, Ringer).

13. MAIN DISTRIBUTION FRAME(MDF)
• It is place where both external and internal cables are terminated.
• It carries all the protectors used in the exchange.
• This M.D.F. is an ideal place for testing purpose.
• Both the internal and the external cables are available at this frame and, therefore, both
external and internal wiring and lines can be tested for this purpose.

14. MAIN DISTRIBUTION FRAME(MDF)

15. FREQUENCIES USED IN TELEPHONY
•High band tone (1216 Hz. to 1645 Hz.)
•Low band tone (701 Hz. to 936 Hz.)
•1 to 5 fall in low band
•6 to 9, 0 fall in high band

16. HOOK SWITCH
•Off-hook for a tip condition or to describe a circuit that is in use (i.e., when a phone call is
in progress)
•On-hook for an idle circuit (i.e. no phone call is in progress)

17. TYPES OF CONNECTION
1) With wires i.e. cables
2) Wireless Microwave Links through
Satellite
CABLES :
1. Underground cables:
These types of cables run under the
Earth
2. Overhead cables

18. FAULTS IN AN EXCHANGE
1. Faults that occur from Line
• Break fault
Disconnection faults
"Telephone is dead".
• Loop fault
Line-Shorting faults
connectors are shorted
• Earth fault:
Wetting of connectors
Connectors can either touch from earth, with other connector or with any conductor (such as
metallic table, frame etc.)
2 . Faults that occur due to instrument
Dial tone breaks after two or three rings.
Instrument circuitry faulty.

19. FACILITY OF TELEPHONE
•CONFERENCE-3 PARTY
•LAST CALLER CALLBACK: 851
•APPOINTMENT REMINDER:852 then dial the time
•LAST NO. REDIAL: 854
•CALL PICK UP: 89-xxxx to pick up a call ringing at another location xxxx.
•CALL TRANSFER: 2 Parties conversing, any party can dial 3rd party, then Conversation
among them Hang-up. The party on line now Talks to 3rd party

20. THANK YOU