Module 1

• Communication is the process of exchanging information.
• Two of the main barriers to human communication are language and distance.
• Human communication took a dramatic leap forward in the late nineteenth century when electricity was discovered and its many applications were explored.
• The telegraph was invented in 1844 and the telephone in 1876. Radio was discovered in 1887 and demonstrated in 1895.
• Marconi is generally credited with inventing radio, but he did not.

  Although he was a key developer and the first deployer of radio, the real credit goes to Heinrich Hertz, who fi rst discovered radio waves,

  and Nicola Tesla, who first developed real radio applications.
• In electronic communication systems, the message is referred to as information, or an intelligence signal.
• The first step in sending a message is to convert it into electronic form suitable for transmission.
• Transducers convert physical characteristics into electrical signals.
• The transmitter itself is a collection of electronic components and circuits designed to convert the electrical signal to a signal suitable for transmission over a given communication medium.
• Transmitters are made up of oscillators, amplifi ers, tuned circuits and filters, modulators, frequency mixers, frequency synthesizers, and other circuits.
• The communication channel is the medium by which the electronic signal is sent from one place to another.
• Many different types of media are used in communication systems,

  including wire conductors, fiber-optic cable, and free space.
• A receiver is a collection of electronic components and circuits that accepts the transmitted message from the channel and converts it back to a form understandable by humans.
• most communication equipment incorporates circuits that both send and receive. These units are commonly referred to as transceivers.
• Signal attenuation, or degradation, is inevitable no matter what the medium of transmission.
• Attenuation is proportional to the square of the distance between the transmitter and receiver.
• Noise. Its affect is experienced in the receiver part of any communications system.
• The measure of noise is usually expressed in terms of the signal-to-noise (S/N) ratio (SNR), which is the signal power divided by the noise power and can be stated numerically or in terms of decibels (dB).
• The simplest way in which electronic communication is conducted is one-way communications, normally referred to as simplex communication.
• The form of two-way communication in which only one party transmits at a time is known as half duplex communication
• People communicating with one another over the telephone can talk and listen simultaneously called full duplex communication.
• An analog signal is a smoothly and continuously varying voltage or current.
• Digital signals do not vary continuously, but change in steps or in discrete increments.
• Most digital signals use binary or two-state codes.
• Modulation makes the information signal more compatible with the medium.
• Multiplexing allows more than one signal to be transmitted concurrently over a single medium.
• Putting the original voice, video, or digital signals directly into the medium is referred to as baseband transmission.
• The information or intelligence to be sent is said to be impressed upon the carrier. The carrier is usually a sine wave generated by an oscillator. The carrier is fed to a circuit called a modulator along with the baseband intelligence signal. The intelligence signal changes the carrier in a unique way. The modulated carrier is amplifi ed and sent to the antenna for transmission. This process is called broadband transmission.
• The range of electromagnetic signals encompassing all frequencies is referred to as the electromagnetic spectrum.
• Frequency is the number of times a particular phenomenon occurs in a

  given period of time.
• Wavelength is the distance occupied by one cycle of a wave, and it

  is usually expressed in meters.
• Bandwidth is that portion of the electromagnetic spectrum occupied by a signal. It is also the frequency range over which a receiver or other electronic circuit operates. More specifically, bandwidth is the difference between the upper and lower frequency limits of the signal or the equipment operation range.
• The modulation process causes other signals, called sidebands.
• In practice, this means that there are many more 10-kHz channels at the higher frequencies than at the lower frequencies.
• The Federal Communications Commission (FCC) was formed in 1934 to regulate interstate and foreign communication.
• The International Telecommunications Union (ITU), an agency of the United Nations that is headquartered in Geneva, Switzerland.
• The National Telecommunications and Information Administration (NTIA) performs a similar function for government and military services.
• World Administrative Radio Conferences, held approximately every two years.
• Standards are specifications and guidelines that companies and individuals follow to ensure compatibility between transmitting and receiving equipment in communication systems.