Communications Introduction

Mr. Hennessy/Mr. DiMeglioUxbridge High School

1/08

Communications is Defined as

The sharing of thoughts and ideas through a variety of mediums from a sender to a receiver and the message must be comprehended.

All the ways (radio, phone, computer, semaphore, etc.) in which information is sent, received, stored, retreived and understood.

Semaphore is the use of flags to send a message

Communications System Model

OUTPUTOUTPUTINPUTINPUTGoalGoal

FEEDBACKFEEDBACK

ENCODETRANSMITINGCHANNELRECEIVERDECODE

PROCESS

The Message

Communications Systems - Process encode to prepare a message for transmission.

Encoding is when a signal is translated into a form that the communications system can transmit

transmit to send a message down a channel (wires, fiber optics (using a laser), coaxial cable, sound waves, radio waves, etc. The medium is the way the signal must be sent for that channel.

receive to get a message or take delivery of the signal decode to change a signal back from the channel

medium into something you can understand. For example; when the electrical signal in a phone is converted to audio, a form that is useful to the receiver.

Communications Systems - Process Destination – The receiver of the information. A

person, computer or other machine. Storage – Information can be stored or archived

for later use. Information can be stored in files and books (hard copies), electronically on hard drives, flash drives, media cards, CD’s or DVD’s music files, photographs or video tapes.

Retrieval – Information that is stored must be able to be retrieved and a system must be in place for the retrieval. Dewey Decimal Classification is an example of a system used in libraries across the country for retrieval of books.

Signal, Signal: is the part of a communication

system that carries information in a medium.

In wires the signal is sent by moving electrons. (electricity)

Fiber Optics signal is light Air would be sound waves. Space uses electromagnetic waves either

high frequency radio waves or microwaves

Analog vs Digital Analog signals: Analog signals

are continuous and vary within some range, rather than using an on and off pattern. The graph of an analog signal is a continuous wave with peaks and valleys.

Digital signals: Digital signals have a limited set of numerical values, and are either on or off or 0’s and 1’s.

Fiber Optic Cable

Fiber Continued/ Refraction

During Refraction, light passes from one medium into another. When the densities of the medium vary, the light that passes through them will either slow down or speed up, therefore changing the angle of the light.

This bending is call the angle of refraction.

Total internal refection Total internal reflection confines light within

optical fibers (similar to looking down a mirror made in the shape of a long paper towel tube).

Because the cladding has a lower refractive index, light rays reflect back into the core if they encounter the cladding at a shallow angle (red lines).

Critical Angle

A ray that exceeds a certain "critical" angle escapes from the fiber (yellow line). 

The benefit is not having to regenerate the signal as often in a fiber optic cable.

Fiber Continued Because you can send many frequencies within a

single fiber and there is no magnetic fields that are produced from the light signal, there is no interference noise that is produced. This allows many signals on the same line simultaneously. Is a big advantage to Optical Fiber.

Cable vs. Fiber

Why use fiber optic cable or copper wire? When a signal is produced in a copper wire

you also induce a magnetic field around that wire. Because there are unusually bundles of wires that are twisted together the magnetic fields that surround the wires tend to create an interference called “cross talk” or noise.

Typical Coaxial cable wire

A. Protective PVC B. Copper conductor (Shield layer)

C. Dielectric material D. Signal conductor