Thursday, 26 December 2013

Some impotent tips to create different symbols through your computer Keyboard with a combination of Alt and Numbers from 0 to 9
Alt       +          1          =         
Alt       +          2          =         
Alt       +          3          =         
Alt       +          4          =         
Alt       +          5          =         
Alt       +          6          =         
Alt       +          7          =          •
Alt       +          8          =         
Alt       +          9          =         
Alt       +          10       =         
Alt       +          11       =         
Alt       +          12       =         
Alt       +          13       =         
Alt       +          14       =         
Alt       +          15       =         
Alt       +          16       =         
Alt       +          17       =         
Alt       +          18       =          ↕
Alt       +          19       =         
Alt       +          20       =          ¶
Alt       +          21       =          §
Alt       +          22       =         
Alt       +          23       =         
Alt       +          24       =          ↑
Alt       +          25       =          ↓
Alt       +          26       =          →
Alt       +          27       =          ←
Alt       +          28       =         
Alt       +          29       =          ↔
Alt       +          30       =         
Alt       +          31       =         
Alt       +          33       =          !
Alt       +          34       =          “
Alt       +          35       =          #
Alt       +          36       =          $
Alt       +          37       =          %
Alt       +          38       =          &
Alt       +          39       =          ‘
Alt       +          40       =          (
Alt       +          41       =          )
Alt       +          42       =          *
Alt       +          43       =          +
Alt       +          44       =          ,
Alt       +          45       =          -
Alt       +          46       =          .
Alt       +          47       =          /
Alt       +          48       =          0
Alt       +          58       =          :
Alt       +          59       =          ;
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Monday, 16 December 2013


Airplane engines may be classified as driven by propeller, Jet, Turbojet, and Rocket. Most engines originally were of the internal-combustion, piston-operated type, which may be air-or liquidcooled. 


During and after world war II, duct-type and gas-turbine engines became increasingly important, and since then jet


propulsion has became the main form of power in most commercial and military aircraft. The landing gear is the understructure that supports the weight of the craft when on


 the ground or on the water and that reduces the shock on landing. there are five common types-the Wheel, Float, Skid, and Ski types.

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Saturday, 7 December 2013

A communication satellite is, in fact, a microwave transmitter/receiver, known as earth stations, or ground stations. The satellite receives transmission on one frequency band(uplink), amplifies or repeat the signal, and transmit it on another frequency (downlink). A single orbiting satellite will operate on a number of frequency bands, called transponder channels, or simply transponders.

Thus, the satellites are transponders that are set in geostationary orbits directly over the equator. These geostationary orbits are 36000 km from the Earth’s surface. At this point, the gravitational force placed on the satellite that wants to filling it out into space. 
Microwaves use line of sight propagation. Microwaves frequency ranges from 1 to 300 GHz. Microwaves are used in cellular phones, satellite networks and wireless LANs. Microwaves are unidirectional. It is useful in unicasting i.e. one to one communication. To travel longer distances, the antennas must be taller. There should not be any obstacle in between. Usually mountain tops are the preferred positions for the antennas to avoid obstacles. Microwave can travel for one direction at a time. Fro two way communication two frequencies need to be allocated. At both ends a transceiver for operating two different frequencies. Repeaters are used along with antennas to generate the signal. Microwave is inexpensive and it allows you to communicate from anywhere.
Microwave is commonly used for both voice and television transmission.
There are two types of  antennas used for microwave communications, 
1. The parabolic dish and 
2. The horn.
The Parabolic dish is 3m in diameter and its shape is like a parabola. It focuses a narrow beam to achieve line of sight transmission. The parabolic dish acts a funnel, catching wide range of waves and directing to a common point.

In horn antenna, the outgoing transmission is broadcast up a stem and deflected outward in series of narrow parallel beams by the curved head. The scooped shape of the horn collects the received transmissions and deflected down into the stem.

Friday, 6 December 2013

Infrared signals used for short range communication. It has the frequency range from 300 GHz to 400 THz. It has wavelength from 1 mm to 770 mm. Infrared communications is achieved by using the transmitters/ receivers that modulate infrared light. Transceivers must be within the line of sight of each other directly or via reflection.
One disadvantage of infrared is that is dose not penetrate walls. We can not use infrared outside a building because sun’s rays contain infrared waves which can interfare with the communication.
When we infrared remote control, we do not interfare with the use of remote by our neighbours. It can be used for digital data transmission with high data rate.

As no licensing is required, there is no frequency distribution issue in case of infrared. The association that has steup standards for communication is called Infrared Data Association. IrDA port is used to communicate a wireless keyboard to communicate with PC.
The radio waves are omnidirectional. While the microwaves are directional. Radio waves are used for one sender and multiple receivers i.e. for multicusting property. Because of this multicast communication, it is used by radio, television, cordless phones and pagers. Radio waves is a general term to encompass frequencies in the range 3 KHz to 1 GHz. The microwaves ranges in frequencies between 1 to 300 GHz. Broadcast radio term may be informally used for the FM radio and VHF television and number of data networking applications.
As the radio waves are omnidirectional, they do not require dish-shaped antennas with precise alignment. Radio waves used omnidirectional antennas that send the signals in all directions. We can  have different types of antennas based on wavelength and strength. Radio waves can penetrate walls. It can be considered as an advantage e.g. AM radio can receive signals inside the building. It has the disadvantage that radio waves band is relatively narrow and if we subdivide it ferther, it becomes narrower resulting in lower data rate for digital communications. Another problem with the radio waves are multipath interference. Reflection from different sources can create multiple paths between antennas which is evident when TV receiption displays multiple images. But because of longer wavelength, radio waves suffer less attenuation.

Radio waves band is regulated by authorities like FCC in United States
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Thursday, 5 December 2013

For wireless communication, signals can travel from source to destination in several ways they are ground propagation, sky propagation and line-of-sight propagation.
Radio waves travel through the lowest portion of the atmosphere. These low frequency signal emanate in all directions from the transmitting antenna and follow the curvature of the planet. Distance depends on the amount of power in the signal. This type of propagation is called Ground Propagation.
Higher frequency radio waves propagate upward into the layer of the atmosphere where particles exist as ions (ionosphere). This type of transmission allows greater distances with lower power output and is called as Sky Propagation.
When very high frequency signals are transmitted in straight lines directly from antenna to antenna, it is called line-of-sight propagation. Antennas must be directional, facing each other, and either tall enough or close enough together not to be affected by the curvature of the earth.
 The part of electromagnetic spectrum, defined as radio and microwaves, can be further divided into eight ranges, called bands. These bands are rated from very low frequency (VLF) to Extremely High frequency (EHF)
Very Low Frequency :: These waves propagate as surface waves, usually through air, sometimes through water. VLF may be affected by atmospheric noise. VLF waves are usually used for long range radio navigation and submarine communication.
Low Frequency :: these waves propagate as surface waves. Attenuation is higher during daytime. These waves are usually used for long range radio navigation or navigational locatiors.
Middle Frequency :: These waves rely on line-of sight antennas to increase and control absorption problems. These waves are used for AM radio, radio direction finding and emergency frequencies.
High Frequency :: these waves are used for amature radio, citizen’s band radio, international broadcasting, military communication, telephone and telegraph.
Very High Frequency :: these waves use line-of-sight propagation and are used for VHF television, FM radio, aircraft AM radio and aircraft navigation.
Ultra High Frequency :: these waves use line-of sight propagation and are used for television, mobile phone, cellular radio, paging and microwave links.
Super High Frequency :: these waves are transmitted either line-of-sight or into the space. They are used for terrestrial and satellite microwave and radar communication.

Extremely High Frequency :: These waves are transmitted into space and are used for radar, satellite and experimental communication. 
Light actually originates from the accelerated motion of electrons of atom. Atoms emit light in tiny packets of energy called photons. Photons move through space as electromagnetic waves, which are a form of energy with magnetic and electrical components. The electromagnetic waves travels at the same speed of light (c) through vacuum, no matter what their frequency the number of oscillations per second of a wave is called its frequency, f, and is measured in Hz. The distance between two consecutive maxima is called the wave length denoted by (lamda)

The classification of electromagnetic waves according to frequency is the tlectromagnetic spectrum. Light that we is only one part of this whole spectrum. The electromagnetic spectrum is a contiuous range of waves extending from radio waves to gama rays. The description names of the sections are merely a historical classification, for all waves are the same in nature,
differing principally in frequency and wavelength; all travel at the same speed. The underlying principle that makes light and all other electromagnetic waves travel at one fixed speed is the conservation of energy.

Wednesday, 4 December 2013

Fiber optic cable is now extensively used as a communication medium for backbone networks due to its low cost wide bandwidth. Its data transfer rate now arrived at 1600 Gbps. Some cable TV companies used a combination of optical fiber and coaxial cable. Here optical fiber provides the backbone network and the coaxial cable gives service connection to the  users. 100Base-FX and 1000Base-X LAN uses optical fiber cable.
Fiber optic cables have several advantages over the metallic cables such as coaxial cable and twisted-pair.
HIGHER BANDWIDTH:: fiber optic cable can provide very high bandwidth and therefore high data rate then the coaxial and twisted-pair cable.
LESS ATTENUATION:: It offers less attenuation  then metallic cables. Hence signal can travel up to 50 Km without repeater in a fiber optic cable.
IMMUNITY TO ELECTROMAGNETIC INTERFERENCE :: Electromagnetic noise cannot affect a light signal traveling through a fiber  optic cable.
RESISTANCE TO CORROSION :: Fiber optic cables are not affected by corrosive substances.
LIGHT WEIGHT :: These are much lighter in weight then metallic cables.
GREATER IMMUNITY TO TAPPING :: Light signals are very difficult to tapped then an electrical signal. Hence signal passing through a fiber optic cable has greater immunity to tapping.
Despite of many advantages, fiber optic cable has some disadvantages also. These are ::
DIFFICULT TO INSTALL AND MAINTAIN :: Since fiber optic cable is a new technology, so skill personal for installation and maintenance of fiber optic cable is scarce.
UNIDIRECTIONAL SIGNAL PROPAGATION :: Light propagation is unidirectional. So if we require bidirectional communication, we need two fiber cables.

COST:: the fiber optic cables and the interfaces are expansive till date in comparison to other types of cables.

Tuesday, 3 December 2013

Fiber optic cable is a communication medium made of glass or plastic that can transmite signals in the form of light. In optics there is a principle which states that when a beam of light travels from denser medium to rerer medium then it deviates away from the normal drawn at the point of incidence at the junction of the two media.
If the angle of incidence is such that the angle of refraction is 90 degree then the angle of incidence is called critical angle. Now if the angle of incidence is greater then critical angle then the refracted ray would re-enter into the denser medium. This phenomenon is called total internal reflaction.
In optical fiber light signals travel by following the principle of total internal reflaction. In an optical fiber, a glass or plastic core is surrounded by a cladding of less dense glass or plastic. This difference in density facilities total internal reflection for a light signal that travels through the cable.
Current technology provides two modes of light propagation through an optical fiber. These two modes are MONO MODE and MULTI MODE. Further fiber optic cable has two varieties STEP INDEX and GRADED INDEX.
In Step index fiber, core and cladding has a definite boundary. In graded index fiber, density of the fiber is gradually decreases from inner core to the outer boundary.
In mono mode, step index fiber is used. Mono mode fibers are of the order of 8-10 microns in diameter. Mono mode fibers are costly and they can transmit light signal to a longer distance then multi mode fiber. A highly focused beam of light is injected into the fiber at an incident angle close to the horizontal line. Its density is also much lower so that the critical angle is almost equal to 90 degree. Therefore the reflected beam also propagates in almost horizontal line. The delay is minimum here.
Multi mode operation can transmit multiple beams of light signal at a time. These fibers are thicker in diameter then the mono mode fiber, of the order of 50 microns. These are cheaper but can transmit signal to a shorter distance. In multi mode both step index and graded index cables are used.

Sunday, 1 December 2013

Bus is an electrical way through which the processor communicates with the internal and external devices. Buses are assemble with the computer.
Bus transfer data between the computer sub-system. It sends instructions and commands to and from the processor.
It connects all internal computer peripherals devices which can easily communicate with the CPU.
There are mainly three types of buses.
                1.   Address bus
                2.   Data bus or memory bus
                3.   Control bus
Address Bus::
Address bus selects the memory address where data comes from and goes to input and output respectively and address bus carries addresses information in most processors, memory is connected to the processor  with separate address and data buses.
Acomputer with a 32 bit address bus can directly address 4gb of physical memory, with 36 bits can address 64 gb.
Data bus or Memory bus::
The data bus is also referred to as memory bus it can connect the memory sum system to the chipset and the processor in same computer system, the processor and memory buses do specific task it connect the CPU to the main memory.
Control Bus::
Control bus also called timing control bus. It is used by the CPU to direct and monitor the actions of other computer. It transmits read, write, interrupt and acknowledge signals. It also directs the CPU and Monitor.the action of the other functional areas of the computer.
There are also two other buses. They are Local memory bus and Case bus.
Local memory bus directly mounted on printed circuit board (PCB) it provides a common communication path among major components as chips.
It is a single and efficient muster bus. It can read from and write to data buses in a unique way.

A case bus connects a processor to its internal or external memory case or cases.
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