Signals and Codes

1. Section 1 Signals and Telecommunication Chapter 18 Signals and Codes • A signal is anything that serves to direct, guide, or warn. • Signals can be sent in the form of gestures, flags, lights, shapes, colors, or even electric current. • Codes are used to send signals. • Acode is a set of rules used to interpret data. • Signals are sent in many different forms. • Both electricity and electromagnetic waves offer excellent ways to send signals that can travel long distances. • A transducer converts signals. • A speaker converts an incoming electrical signal into sound.

2. Section 1 Signals and Telecommunication Chapter 18 Transducers

3. Section 1 Signals and Telecommunication Chapter 18 Signals and Codes

4. Section 1 Signals and Telecommunication Chapter 18 Telecommunication • Telecommunication is the sending of visible or audible information by electromagnetic means. • An analog signal varies continuously within a range. • An analog signal is a signal whose properties, such as amplitude and frequency, can change continuously in a given range. • Analog signals consisting of radio waves can be used to transmit picture, sound, and telephone messages.

5. Section 1 Signals and Telecommunication Chapter 18 Telecommunication, continued • Digital signals consist of separate bits of information. • Adigital signal is a signal that can be represented as a sequence of discrete values. • A binary digital signal consists of a series of zeros and ones. • Each binary digit is called a bit. • In electrical form, 0 and 1 are represented by the two states of an electric current:off (no current present) and on (current present).

6. Section 1 Signals and Telecommunication Chapter 18 Binary Code

7. Section 1 Signals and Telecommunication Chapter 18 Telecommunication, continued • Sound can be stored digitally. • Sound can be described by noting the air pressure changes. • The air pressure is measured in numbers and represented in binary digits. • Digital signals can be sent quickly and accurately. • Digital signals have many advantages over analog signals. • Noise and static have less effect on digital transmissions.

8. Section 1 Signals and Telecommunication Chapter 18 Telecommunication Today • Optical fibers are more efficient than metal wires. • An optical fiber is a transparent thread of plastic or glass that transmits light. • These fibers carry signals that are represented by pulses of light emitted by a laser. • The optical-fiber system is lighter and smaller than the wire-cable system. • A single optical fiber can carry 11 000 conversations at once using the present coding system.

9. Section 1 Signals and Telecommunication Chapter 18 Telecommunication Today, continued • Relay systems make it possible to send messages across the world. • Microwave towers should be tall. • Communications satellites receive and transmit electromagnetic waves. • A satellite receives a microwave signal, called anuplink, from a ground station on Earth. • The uplink signal has frequency of around 6 GHz. • The satellite then processes and transmits a downlink signal to another ground station. • The downlink signal typically has a lower frequency of about 4 GHz.

10. Section 1 Signals and Telecommunication Chapter 18 Telecommunication Today, continued • Many communications satellites have geostationary orbits. • These satellites orbit Earth every 24 hours, the same amount of time it takes for Earth to rotateonce. • The position of the satellite relative to the ground doesn’t change. • The orbit of this type of satellite is called ageostationary orbit, or ageosynchronous orbit.

11. Section 2 Telephone, Radio, and Television Chapter 18 Telephones • The electret microphone vibrates with sound waves, creating an analog signal. • In anelectret microphone, an electrically charged membrane is mounted over anelectret, which is a material that has a constant electric charge. • The electrical signal that is created is transmitted as variations in an electric current between your telephone and the telephone of the person to whom you are talking. • The movement of the speaker cone converts the analog signal back into sound waves.

12. Section 2 Telephone, Radio, and Television Chapter 18 Telephone The sound waves from your voice are transformed by the microphone into an analog electrical signal. A speaker converts the analog electrical signal back to sound waves.

13. Section 2 Telephone, Radio, and Television Chapter 18 Telephones, continued • Telephone messages are sent through a medium in physical transmission. • Sometimes telephone conversations travel a short distance by wire and then are carried by light through fiber-optic cables. • The electrical signal is converted into a light or optical signal by a laser diode. • Transmission of signals by wires or optical fibers is calledphysical transmission.

14. Section 2 Telephone, Radio, and Television Chapter 18 Telephones, continued • Messages traveling longer distances are sent by atmospheric transmission. • Atmospheric transmission is the passage of an electromagnetic wave signal through the atmosphere between a transmitter and a receiver. • Computers help route calls. • Cellular phones transmit messages in the form of electromagnetic waves. • A cellular phone is a small radio transmitter/receiver, ortransceiver.

15. Section 2 Telephone, Radio, and Television Chapter 18 Radio and Television • Sound waves are converted to electromagnetic waves for radio broadcast. • An electronic device called an amplifier increases the power of the weak signal produced by a microphone. • The oscillator in the transmitter produces a carrier, which is a signal of constant frequency and amplitude. • A carrier is a wave that can be modulated to send a signal.

16. Section 2 Telephone, Radio, and Television Chapter 18 Radio and Television, continued • In a specialized circuit in the transmitter the audio signal and the carrier signal combine, and the audio signal changes, or modulates, the carrier wave. • Modulate means to change a wave’s amplitude or frequency in order to send a signal. • The result isa signal of constant frequency with an amplitude that is shaped by the audio signal.

17. Section 2 Telephone, Radio, and Television Chapter 18 Radio and Television, continued • Modulation can be either AM or FM. • Most broadcast carrier waves are modulated either byamplitude modulation (AM) or byfrequency modulation (FM). • In amplitude modulation, the audio signal increases and decreases the amplitude of the carrier wave in a pattern that matches the audio signal. • In frequency modulation, the audio signal affects the frequency of the carrier wave, changing it in a pattern that matches the audio signal

18. Section 2 Telephone, Radio, and Television Chapter 18 Radio and Television, continued • Higher frequency transmissions can follow only a simple straight line calledline-of-sight transmission. • AM frequencies between 540 and 1700 kHz can travel asground waves, which can follow the curvature of the Earth for some distance, unlike line-of-sight transmissions. • AM radio stations use sky waves to broadcast long distances. • Radio receivers convert electromagnetic waves back into sound. • The antenna of your radio receiver works as a transducer.

19. Section 2 Telephone, Radio, and Television Chapter 18 Radio

20. Section 2 Telephone, Radio, and Television Chapter 18 Radio and Television, continued • Television sets convert electromagnetic waves back into images and sound. • The carrier wave is passed to a detector that separates the audio and video electrical signals from the carrier. • The picture tube of a black-and-white television is a large cathode- ray tube or CRT. • Acathode-ray tube is a tube that uses an electron beam to create a display on a phosphorescent screen.

21. Section 2 Telephone, Radio, and Television Chapter 18 Radio and Television, continued • Color picture tubes produce electron beams. • Color picture tubes in some televisions produce three electron beams, one for each of the primary colors of light: red, blue, and green. • Each group of three dots is apixel, which is the smallest element of a display image

22. Section 2 Telephone, Radio, and Television Chapter 18 Television

23. Section 3 Computers and the Internet Chapter 18 Computers • A computer is an electronic device that can accept data and instructions, follow the instructions, and output the results. • Computers have been changing greatly since the 1940s. • The first electronic computer was the Electronic Numerical Integrator and Computer (ENIAC). • Computers carry out four functions. • Digital computers perform four basic functions: input, storage, processing, and output.

24. Section 3 Computers and the Internet Chapter 18 Computers, continued • Computer input is in the form of binary code. • Computers process binary data, including numbers, letters, and other symbols, in groups of eight bits. • Each bit can have only one of two values, usually represented as 1 and 0. • A group of eight bits is called abyte. • Computers must have a means of storing data. • Both hard drives and floppy drives are referred to asmagnetic media because theyuse disks coated with a magnetizable substance.

25. Section 3 Computers and the Internet Chapter 18 Computers, continued • Random-access memory is used for short-term storage of data and instructions. • Random-access memory is a storage device that allows a computer user to write and read data; it is the amount of data that the memory chips can hold at one time (abbreviation, RAM) • Read-only memory is for long-term storage of operating instructions. • Read-only memory is a memory device that contains data that can be read but cannot be changed (abbreviation, ROM)

26. Section 3 Computers and the Internet Chapter 18 CPU, RAM, and ROM

27. Section 3 Computers and the Internet Chapter 18 Computers, continued • Optical storage devices can be more permanent than magnetic disks. • Compact discs (CDs) and digital versatile discs (DVDs) are called optical media because the information on them is read by a laser light. • Operating systems control hardware. • The hardware is the parts or pieces of equipment that make up a computer. • The software is a set of instructions or commands that tells a computer what to do; a computer program. • The operating system is the software that controls a computer’s activities.

28. Section 3 Computers and the Internet Chapter 18 Computers, continued • The processing function is the primary operation of a computer. • Computing or data processing is carried out by thecentral processing unit, or CPU. • Chips have many components. • This chip, or microprocessor, consists of millions of tiny electronic parts, including resistors, transistors, and capacitors. • Logic circuits in the CPU make decisions. • The heart of the CPU is anarithmetic/logic unit, or ALU, which performs calculations and logic decisions. • The CPU also contains temporary data storage units, called registers.

29. Section 3 Computers and the Internet Chapter 18 Computers, continued • The CPU’s logic gates can be built up to evaluate data and make decisions. • A logic gate can open or close a circuit depending on the condition of two inputs. • One kind of logic gate is called an AND gate. • An AND gate closes the circuit and allows current to pass only when both inputs are in the “on” position. • Another type of logic gate is called an OR gate. • An OR gate closes the circuit and allows current to pass when one of the input is in the “on” position.

30. Section 3 Computers and the Internet Chapter 18 A Logic System

31. Section 3 Computers and the Internet Chapter 18 Computer Networks and the Internet • In local area networks, or LANs, all PCs are connected by cables to a central computer called a server. • A server consists of a computer with lots of memory and several hard-disk drives for storing huge amounts of information. • The Internet is a worldwide network of computers. • The Internet is a large computer network that connects many local and smaller networks all over the world.

32. Section 3 Computers and the Internet Chapter 18 Computer Networks and the Internet, continued • You need three things to use the Internet. • You need a computer with a modem to connect the computer to a telephone line. • The wordmodem is short for modulator/demodulator. • You need a software program called an Internet, or Web, browser. • You need a connection to an Internet service provider, or ISP.