primitive telecomunication

Indian telephones

The beginning of voice on wires:

28th January 1882, is a Red Letter Day in the history of Telephones in India. On this day the Telephone Exchanges in Calcutta, Madras, and Bombay were declared open. The exchange at Calcutta named "Central Exchange" was opened on 30-06-1882; the Central Telephone Exchange had 93 subscribers. In 1883 First telephone communication was established between Calcutta and Howrah through a cable laid beneath the floating Howrah Bridge.

The independent India had a few telephone lines. They were concentrated in metros like Bombay, Calcutta, Delhi, and Madras.

The railway control circuits were using the phone system for trains’ movement.

            It was still a manual switching system in which every call is to be put through manually. Gradually the system spread to state capitals and the district headquarters. 

Primitive communication system 

        

A small telephone exchange was opened in a district headquarter to start with. It was placed near the market area, or some suitable place centrally located in the town. Very few open wires served the main offices like the post office, polish station, administrative offices and business houses, and some VIPs connections. All connections taken together were probably less than 50[DELs] direct exchange lines.

The manual call switching board [switch board] was simple with indicator lamps to indicate the condition of phone lines by glowing small line lamps. Lines were terminated on line terminals [hole-like jacks]. A line lamp and associated line jack were the terminals of subscribers’ lines. To interconnect the callers to called subscribers [subs], a pair of connecting cords were used.

The telephone operator has to respond to the demand of the calling sub, answering the calling sub by inserting a cord into a line jack. Ascertain the called number and connect to the called line and give a manual ring to the called sub so that he lifts the handset; thus the connection is established between the caller and the called numbers.

This was a simple manual exchange; the power supply was managed centrally at the exchange itself and it was called CBNM [central battery nonmultiple] exchange system.

Initial exchanges for telephony were of this nature, throughout the nation in India prior to 1970 or so. The telephone operator was the software behind the call-switching activity.

Each subscriber was charged a monthly rent of Rupees 50/ towards the service given. The local calls were free of cast for the entire month.

Trunk circuits were established connecting with adjacent district headquarters and taluk headquarters. Some large villages were also connected with PCOs. Open wire lines [of tubular iron poles] were used. To construct open wire lines and to maintain these lines in working order; a separate staff called the line staff was recruited on a permanent basis. They were called linemen; line inspectors etc. The switching apparatus was maintained by a trained technician.

Multiple operators were used for rotational round-the-clock duties. A senior man among them has to supervise the operational activity; and manage the overall system.

The operator has to handle local calls, trunk calls, book the ticket, for trunk calls and establish trunk calls and charge the calls by noting the time of call connected and call disconnected.

These trunk calls (established) tickets were to be dispatched to the revenue accounting office in the divisional office, where the Divisional engineer’s office was established.

On the engineering side Divisional Engineer’s office, the Sub-divisional Engineer’s office, and the junior engineers’ office were established to manage the technical affairs of the working system.

             The background:

                          1837-telegraph

1864-existence of radio waves

1875-invention of telephone

1897-strowger exchange

1901-transmission of radio signals

1904-vaccum tube diode

1918-super heterodyne radio receiver

1948-mathematical theory of digital communication

1948-invention of transistor

1955-proposal of satellite communication

1958-silicon integrated circuit

1962-telstar satellite-bell lab

1966-use of fiber as a dielectric waveguide

1971-pocket switching theory

Bidar being the district headquarters had also a telephone system. In 1974 there were about 300 telephone lines in Bidar town. The primitive system of local telephone lines was, all overhead iron wires hanging along the local roads on tubular posts along the streets. They were terminated on a manual switchboard. The manual switching of local calls and trunk calls was done by telephone operators (TOs). Telephony was a new flourishing business undertaken by the communication ministry and the department was known as the Posts and Telegraphs (P&T) department.

            Talented taught students either of SSLC /PUC or of degree were regularly inducted or absorbed in the system, to cope up with the growth of telecommunication service.

I was a 1973 science graduate (B.Sc.) and I was inducted as TO in 1974. The Gulbarga division had four districts covering Bellary, Raichir, Gulbarga, and Bidar. Gulbarga local area had a 700 lines telephones system, all managed manually. The telephone operator was the blood and nerve of the operating system for putting through calls and serving each and every inquiry of the customers.

            Telephone being the fastest method of communication was established in cities and towns. The growth and modernization were slow.

            Trunk lines were constructed by erecting tubular posts along the state highways and other road networks. The Indian railways used the service of telecom for trains’ movement. The trains' control and block lines were maintained by P&T. The engineering supervisors, technicians, sub-inspectors ‘and linemen were the people to construct and maintain the trunk lines. Two separate parallel conducting wires which enable the path for the speech current to pass through them were called trunk circuits. All these local lines and trunk lines were terminated on manual switchboards and were handled by TOs.

Normally all taluka headquarters were connected to the district headquarters by trunk circuits. And Bhalki was one such taluka in Bidar district. There was a trunk line between Bhalki and Bidar along the railway route. This route was further extended to Kamalnagar, Aurad, and Santapur. Some villages were directly terminated to the board and these lines were known as PCOs (public call offices). A post office of the village houses a phone instrument and the postmaster keeps the call records. There were about 70 working lines at the Bhalki telephone exchange. There were five telephone operators to handle the telephone traffic of the town. One of them would be the head operator. He was supposed to keep all the records of calls established and dispatch the tickets to the divisional office for the calculation of call charges on individual lines. The exchange system was very simple at Bhalki. A CB non-multiple board, a small MDF, a battery room, and a carrier system of 1+3 type, were housed in a rented building. The external plant was, a bit of cable laid up to the Gunj main circle and local lines feeding the shops. The engineering supervisor groups Bidar was in charge of the system.

            The customers who used these services were billed monthly and if the bill is not paid, the line was disconnected temporarily to press the party to pay the dues. The revenue collection was thus regular and prompt. But the main problem was the manual-working, especially during night hours, human nature is to sleep but they were made to work like machines and they did not.

            These early telephone lines were of open wire type. The iron wires (galvanized) were drawn right from the switching office to the subscribers’ premises, along the streets. The trunk lines were going along the roads and they were exposed to wind currents, the rains, and the night colds and mid-day heat of summer. There was ware and tare. If the line is loose or the span length from pole to pole is kept long, the wires got contact with each other due to wind disturbances, and the line is short-circuited and hence dead. Sometimes there will be a break of conductors and supporting posts slanting due to heavy rains. These were to be attended promptly to restore the telephone services. Telegraph lines were also working between post offices. A written message was generated known as a telegram and sent to the concerned party.

            This simple system of connecting people manually by building circuits by operators from place to place as a cascade was a well-established practice of manual switching. Suppose that a subscriber at Bhalki wants to communicate with a person at Gangavathi the call is to be routed through Bidar-Gulbarga-Raichur and then to Gangavathi, the terminal destination of the called party. Since there were limited circuits between towns, there used to be delay to establish a call. There will be a lot of waiting time for a call to mature. The average waiting will be more than one hour for any trunk call. And there was no substitute or alternate method to that of calling a person in need. The marketing people, the businessmen the executives were badly in need of telephone services.

            A letter takes 4 days, a telegram takes 24 hours, and a trunk call takes 2 hours, to communicate. A trunk call is a two-way speaking system and no such facility can be had by other means of communication. Thus it was of immense use to a business to happen between two parties placed far away.

            But the service was not steady and there used to be interruptions again and again due to the lines going out of order. Physical lines running kilometers and being exposed to an open environment, caused a lot of inconvenience and the first party to face the angry customer was the on-duty telephone operator.

            A technique to increase the trunk line capacity was developed by building carrier systems on physical lines. The first one such system was a three-channel carrier system. The advent of electronic circuitry in its primitive stage gave rise to these speech carriers working in addition to the physical lines. That is if there existed a physical line between two places, it was possible to increase the circuits to a 1+3 system of trunks. This increased the availability of circuits between two stations and call waiting time was reduced to 50%. This was a milestone in manual telephony.

            Later on, automatic local exchange switches of Strowger technology were introduced in towns and district places. This reduced the burden of connecting local calls manually. The customer on hearing the dial tone has to dial the required number himself. This automatic system was built on the electro-magnetic principle and uni-selectors and two motion selectors were involved in the process of switching a local call. To monitor the working of these selectors, technicians were employed. They used to rectify the faulty switches. Here again, there was a problem of wrong switching due to the switch going faulty. Wrong switching added to the revenue bill of the customer and a cause of dispute.

            Once the internal system is made automatic, the customer has to dial the local number himself. Thus the burden of the operator is reduced to a considerable extent. He has to concentrate on trunk booking, answering incoming trunk lines to receive incoming calls from other stations, and to put-through the booked calls. Unmanned small auto exchanges of lesser capacity were terminated on these trunk boards to put through calls originating from those exchanges.

            At district head quarts, there was larger trunk traffics. Therefore, the numbers of boards were more and the trunk lines were available as multiples at many boards. The boards were called positions. At metros, there were still more positions and hundreds of operators were working continuously round-the-clock. The duty hours of an operator were normally 8 hours. They were coming to duty on shifts. This was the system of manually switching calls.

            Bulk of trunk routes was needed to handle the growing traffic between metros. The coaxial cables were laid between the major metros. Later when electronic integrated circuits were developed, new microwave systems started appearing in the field to build wireless trunk routes. The microwave towers were erected at about a distance of 50km span length. Repeaters were installed at such locations and the station was maintained with batteries and engine alternators. Between1980-85, most of the metros were connected by microwaves. This technical up-gradation gave rise to the availability of plenty of trunk lines between cities. Now, the local and trunk were automatic and subscriber trunk dialing was introduced between many cities. Thus the need for the operator is slowly eliminated from the system. The operators were surplus and they were used for miscellaneous works. The technical manpower was increased to maintain the new systems. During Rajeev Gandhi as prime minister of India, one Mr.Shyam Pitroda came to India and he took the task to create all electronic switching systems. Thus there onwards everything was automatic and by this time most of the surplus staff were either retired or absorbed into service center handling. There were rapid expansions everywhere and a lot of new addition of assets both internal and external systems. The working lines at district headquarters grew tenfold in a span of a decade time.

Thus the communication network grew and works were specialized and a separate internal wing was dedicated to maintain the major trunk routes. Similar to railway zones, telecom regions were established to handle the system effectively.

            All such things happened but most of the village population remained out of this facility. The demand was building up and the service was not available to villages. About 50% of the villages were not having communication links. If there are PCOs, they were not maintained as desired due to technical reasons. Efforts were made to install VPTs. But they did not serve the real purpose.

            Meanwhile, optic fiber cables were developed and being inducted into the system.

These simple optic fibers were having a very large capacity to increase the channels just by replacing the end units of trunk routers. They were cost-effective and more stable and most of the microwaves were replaced by OFC cables. In metros, multi-exchange cables, called junction cables were replaced by OFC cables. Also, interior towns in a district were connected to district headquarters by these optic fiber networks.

            India as a whole when considered, lot of backside activity, for store management, activities at ITI terminals, transport of stores to local store yards, and making available when needed, all such things are to be taken into account. A place of 100 crore people, a vast territory, and a gigantic task force to make things happen. Telecom stores, zonal offices, telecom circles, and divisions were buzzing places with full of activity to organize and to implement the decisions made by heads of the task.

  

Date of birth:     03-08-1951.

Education:   B Sc Maths and Physics.

Employment:

            1974- Telephone operator.

            1980- Telephone inspector.

            1084- Junior Engineer.

            1999- Sub Divisional Engineer.

Retired from service on 01-02-2009.

Some important changes:                                     

• Mores code telegraphy
• Manual telephony
• Electro-magnetic strowger exchanges
• Cross-bar switching systems
• Teleprinter [telex] exchanges  
• Electronic exchanges                                                                                                                                                                                                  

                                                                               

Trunk lines:

• Open wire trunks[physical line]
• Three-channel carrier systems
• Eight channel systems
• Microwave links [line of sight communication links]
• Digital microwave systems
• Optic fiber cables links[light wave guides]

           

                                                                                                                                                               

The Atom

The Atomic Theory:

In 1911, Rutherford proposed a revolutionary view of the atom. He suggested that the atom consisted of a small, dense core of positively charged particles in the center (or nucleus) of the atom, surrounded by a swirling ring of electrons. The nucleus was so dense that the alpha particles would bounce off of it, but the electrons were so tiny, and spread out at such great distances, that the alpha particles would pass right through this area of the atom. Rutherford's atom resembled a tiny solar system with the positively charged nucleus always at the center and the electrons revolving around the nucleus.

Interpreting Rutherford's Gold Foil Experiment: The positively charged particles in the nucleus of the atom were called protons.  Protons carry an equal, but opposite, charge to electrons, but protons are much larger and heavier than electrons.  

In 1932, James Chadwick discovered a third type of subatomic particle, which he named the neutron. Neutrons help stabilize the protons in the atom's nucleus. Because the nucleus is so tightly packed together, the positively charged protons would tend to repel each other normally. Neutrons help to reduce the repulsion between protons and stabilize the atom's nucleus. Neutrons always reside in the nucleus of atoms and they are about the same size as protons. However, neutrons do not have any electrical charge; they are electrically neutral.

Atoms are electrically neutral because the number of protons (+ charges) is equal to the number of electrons (- charges) and thus the two cancel out.  As the atom gets larger, the number of protons increases, and so does the number of electrons (in the neutral state of the atom). 

Each element has its own distinct line spectra.  

To Bohr, the line spectra phenomenon showed that atoms could not emit energy continuously, but only in very precise quantities (he described the energy emitted as quantized). Because the emitted light was due to the movement of electrons, Bohr suggested that electrons could not move continuously in the atom (as Rutherford had suggested) but only in precise steps. Bohr hypothesized that electrons occupy specific energy levels. When an atom is excited, such as during heating, electrons can jump to higher levels. When the electrons fall back to lower energy levels, precise quanta of energy are released as specific wavelengths (lines) of light.

Under Bohr's theory, an electron's energy levels (also called electron shells) can be imagined as concentric circles around the nucleus. Normally, electrons exist in the ground state, meaning they occupy the lowest energy level possible (the electron shell closest to the nucleus). When an electron is excited by adding energy to an atom (for example, when it is heated), the electron will absorb energy, "jump" to a higher energy level, and spin in the higher energy level. After a short time, this electron will spontaneously "fall" back to a lower energy level, giving off a quantum of light energy. Key to Bohr's theory was the fact that the electron could only "jump" and "fall" to precise energy levels, thus emitting a limited spectrum of light.

Properties of elements repeat periodically. Similar elements form a group.

	I	II		III	IV	V	VI	VII	VIII
	H								He
	1								2
	Li	Be		B	C	N	O	F	Ne
	3	4		5	6	7	8	9	10
	Na	Mg		Al	Si	P	S	Cl	Ar
	11	12		13	14	15	16	17	18
	K	Ca		Ga	Ge	As	Se	Br	Kr
	19	20	Transition	31	32	33	34	35	36
	Rb	Sr	metals	In	Sn	Sb	Te	I	Xe
	37	38		49	50	51	52	53	54
	Cs	Ba		Tl	Pb	Bi	Po	At	Rn
	55	56		81	82	83	84	85	86

            Formation of compounds

All things are made up of tiny particles called atoms. Helium, neon, argon, krypton are inert gases. They have 2, 8, 8, and 8 electrons respectively in their outermost shell. If any atom gets eight electrons in the outer shell, it becomes stable. This is the octet rule.

Oxygen has six electrons in the outermost shell. They are called valence electrons. If however, there are eight electrons in its valence shell, it becomes stable. The electron affinity of oxygen is more. By losing electrons into the neighborhood or gaining electrons from the neighborhood, atoms become stable in form [compounds].

Sl no	Name	Symbol	configuration
1	Hydrogen	H	1
2	Carbon	C	2,    4
3	oxygen	O	2,    6
4	Sodium	Na	2,    8,   1
5	Chlorine	Cl	2,    8,   7

Atoms can share electrons to form molecules.

Example:- H2, O2, N2, CO2 [covalent bond formation]

            H─H,  O═O, N≡N,  O═C═O

Atoms can donate electrons to form molecules.[transfer of electrons]

Example:- NaCl , NaOH, CaCO₃, NH₄OH [ ionic bonds]

            Na⁺ Cl^-  , Na⁺ OH^-  ,  Ca²⁺CO₃^2-        NH4⁺ OH^-                

Sodium donated its outer shell electron to chlorine and both have now eight electrons in their outer shell and therefore they are stable.

The earth's atmosphere has N2, O2, CO2, and H2O molecules as gases.

Sea water is H2O with many dissolved compounds like NaCl, MgCl2, CaCl2, MgSO4 CaSO4 etc. Water is a polar molecule and a good solvent.

When oxides of non-metals dissolve into water, the water becomes acidic due to an excess of H+ ions in water. [Acid is formed]. The acids are more reactive.

When hydroxides dissolve in water, the water becomes basic due to an excess of OH- ions.

[Base is formed]. The bases are more reactive.

Therefore compounds can form by;

• Only covalent bonds.
• Only ionic bonds.
• By the combination of both, covalent and ionic bonds.

Chemistry is all about understanding the nature of atoms and the formation of bonds.

Enthalpy change:

While forming new bonds, energy is liberated. Therefore bond formation is exothermic.

(for Carbon to Carbon bond formation, energy is needed from an external source.)

Breaking bonds need energy. Therefore bond breaking is endothermic.

In a chemical change either energy is given out or energy is taken in. Energy is conserved.

Hydrogen and oxygen combine to form water. This is an exothermic reaction.

2H2(g) + O2(g) → 2H2O(l). two molecules of hydrogen gas combine with one molecule of oxygen to form two molecules of water.   

Oxidation and reduction:

Oxidation: - loss of electrons by any species is oxidation.

4Al (s) + 3O2 (g) → 2Al₂O₃ (s)

Aluminum is oxidized to Al2O3

Reduction: - a gain of electrons by any species is reduction.

            ZnO (s) + C (s) →Zn (s) + CO2 (g)

           

            Zinc oxide is reduced to Zn

The Earth's crust:

According to calculations by F. W. Clarke, a little more than 47 percent of Earth's crust consists of oxygen. It occurs mainly in the form of oxides, particularly silica, alumina, iron oxides, lime, magnesia, potash, and soda. Silica functions principally as an acid, forming silicates, and the most common minerals of igneous rocks are silicates. From a computation based on 1,672 analyses of all kinds of rocks, Clarke arrived at the following values for the average percentage composition: SiO₂=59.71; Al₂O₃=15.41; Fe₂O₃=2.63; FeO=3.52; MgO=4.36; CaO=4.90; Na₂O=3.55; K₂O=2.80; H₂O=1.52; TiO₂=0.60; and P₂O₅=0.22. (The total of these is 99.22 percent). All other constituents occur in very small quantities, usually much less than one percent.

The oxides combine in various ways. Some examples are given below.

§                     Potash and soda combine to produce mostly feldspars, but may also produce nepheline, leucite, and muscovite.

§                     Phosphoric acid with lime forms apatite.

§                     Titanium dioxide with ferrous oxide gives rise to ilmenite.

§                     Magnesia and iron oxides with silica crystallize as olivine or enstatite, or with alumina and lime form the complex ferromagnesian silicates (such as the pyroxenes, amphiboles, and biotites).

§                     Any silica in excess of that required to neutralize the bases separates out as quartz; excess alumina crystallizes as corundum.

These combinations must be regarded only as general tendencies, for there are numerous exceptions to the rules. The prevalent physical conditions also play a role in the formation of rocks.

Clarke also calculated the relative abundances of the principal rock-forming minerals and obtained the following results: apatite=0.6 percent, titanium minerals=1.5 percent, quartz=12.0 percent, feldspars=59.5 percent, biotite=3.8 percent, hornblende, and pyroxene=16.8 percent, for a total of 94.2 percent. These figures, however, can only be considered rough approximations