Frequency Spectrum

Band	Range	Uses
Very Low Frequency(VLF)	3KHz-30KHz	Long range Radio Navigation
Low Frequency(LF)	30KHz-300KHz	Radio Beacons
Medium Frequency(MF)	300KHz-3MHz	AM Radio
High  Frequency(HF)	3MHz-30MHz	Citizen Band(CB)/Ship/Aircraft Communication
Very High Frequency(VHF)	30MHz-300MHz	VHF TV, FM Radio
Ultra High Frequency(UHF)	300MHz-3GHz	UHF TV, Cellular phones
Extremely High Frequency(EHF)	3GHz-30GHz	Satellite communication
Superior High Frequency(SHF)	30-GHz-300GHz	Radar, Satellite

Wireless Media

  It is also known as a wireless media. Wireless media transmit and receive electromagnetic signals without and electrical or optical conductor.  Here transmission and reception achieved by means of an antenna. For transmission antenna emits signal into medium and for reception antenna picks up electromagnetic signals from the surrounding medium. The two forms of transmission:

  Directional: - In this, transmitting antenna puts out a focused electromagnetic beam. The transmitting receiving antenna must be aligned, known as Point-to-Point Communication.

   Omni-directional: - In this the transmitted signal spreads out in all direction and be received by many antenna inspite of direction.

According to frequency range the wireless media is divided into three parts:-

·         Radiowave (30MHz-1GHz): Omni directional transmission

·         Microwave (1-40GHz): Point-to-Point Communication

·         Infrared (100GHz-1000 THz light frequencies): Local Point to Point, Multipoint application within confined areas.

Cable Transmission Media Comparison

Cable Transmission Media Comparison

Media	Cost	Ease of Installation	Capacity Range	Attenuation	Immunity from Interference
Unshielded Twisted Pair	Extremely Low	Very simple	1 to 100 Mbps	High, maximum effective range in 100s of meters	Low
Shielded Twisted Pair	Moderate	Simple to moderate	1 to 155 Mbps	High, maximum effective range in 100s of meters	Moderately low
Coaxial cable	Low to moderate	Simple	Varies by size and composition between 1 Mbps to Gbps	High, maximum effective range in low Kms	Moderate
Fiber Optic Cable	Moderate to high	Difficult	10 Mbps to Gbps	High, maximum effective range in 10s of Kms	High

Differences between analog and digital computers.

Analog Computer:

An analog computer is a form of computer that uses the continuously changeable aspects of physical phenomena such as electrical, mechanical, or hydraulic quantities to model the problem being solved. As an analog computer does not use discrete values, but rather continuous values, processes cannot be reliably repeated with exact equivalence.

 

Digital Computer: A digital computer is form computer that uses letters and numbers as inputs in processing and displays the result in monitors or other forms of output devices and can also store the output in memory to be used later. Following are some key differences between digital and analog computer

Analog Computer	No.	Digital Computer
This type of computer uses continuously changeable aspects of physical phenomena.	1	This type of computer runs by turning on and off electricity which are digital signals.
Electrical wave generated from pressure, temperature etc. such changeable data are used as input in analog computers.	2	Letters and numbers are used in digital computer to process data.
Analog computer uses physical devices like plotter etc. to display the output of an operation.	3	Digital computer can display output to monitor or on other devices.
Analog computers are less accurate.	4	Accuracy of digital computers is very high as it can take lot of decimal points into consideration in calculation
Speedometer, slide rule etc. are example analog computer	5	Generally all modern computers are digital computers such PC, laptop, notebook etc.

 

Computer Mouse

A computer mouse is a handheld hardware input device (also called Pointing device) that controls a cursor in a GUI and can move and select text, icons, files, and folders. For desktop computers, the mouse is placed on a flat surface such as a mouse pad or a desk and is placed in front of your computer.