Section 3: Radio Communication Radio Transmission – The music and the words are sent to the radio by radio waves. – The radio’s metal antenna detects the radio waves – The electrons in the antenna vibrate and create a electric current – The information about the music and the words are sent to the speakers – The music and words are transferred to your ears

Section 3:Radio Communication Dividing the Radio Spectrum – Radio Stations are assigned a particular frequency. – Turning the dial of your radio changes frequencies. – The set frequency is called a carrier wave. – The radio station has to send information about the sounds that you are hearing. – The information is sent by modifying the carrier wave.

Section 3:Radio Communication AM Radio (Amplitude Modulation) – Radio Stations broadcasts information by varying amplitude of the carrier wave – Your radio detects these changes – The changing electric current makes the speaker vibrate – 540,000-1,600,000 Hz

Section 3:Radio Communication FM Radio (Frequency Modulation) – The frequency is varied to create FM waves. – The strength of the waves are fixed – FM tends to be more clear than AM – 88 million to 108 million Hz – The frequency is much stronger and more clear than AM

Section 3:Radio Communication Television – Television and radio transmitters are similar. – These signals are broadcasted by a carrier wave. – The audio of TV is broadcasted by FM waves – The color and brightness of the show is broadcasted by AM waves.

Section 3:Radio Communication Cathode-Ray Tubes – The CRT in a color TV produces three electron beams that are focused by a magnetic field and strike the screen. – The screen is specked with rectangular spots. Red Green Blue – These spots are grouped with one of each

Section 3:Radio Communication Cathode-Ray Tubes (cont) – The image is created when the three electron beams of CRT sweep back and forth. – By varying the brightness of each spot in a group the spots form any color.

Section 3:Radio Communication Telephones – Until 1950, human operators were needed to connect many calls. – When you speak into a telephone: A microphone converts sound waves into an electrical signal. The waves are transmitted to and from a microwave tower. – It uses another signal for receiving information from the base station

Section 3:Radio Communication Telephones – The base stations are several kilometers apart. – The area each one covers is called a cell. – If you move from one cell to another the signal automatically switches.

Section 3:Radio Communication Cordless telephones – Like a cellular telephone a cordless phone is a transceiver. – Transceivers transmits one signal and can receive another. – You must be within range of the base unit – Many cordless phones have frequency buttons.

Section 3:Radio Communication Pagers – Allows messages to be sent to a small radio receiver. – A caller leaves a message at a terminal – At the terminal the message is changed into a signal. – The signal is transmitted to the pager after receiving a ID number. – Newer pagers can send data and also receive.

Section 3:Radio Communication Communications Satellites – Thousands of satellites have been launched into orbit. – A station broadcasts a high-frequency microwave signal to the satellite. – The satellite receives the signal, amplifies it and then transmits it to a certain area on the globe. – The frequencies are different than those on earth.

Section 3:Radio Communication Satellite Telephone Systems – IF you have a moble telephone, you can make a phone call when sailing across the ocean. – The phone sends a direct signal to a satellite. – The call is passed on to the telephone network. – Satellite links work well for one-way transmissions – Long term delays are common in two-way transmissions.

Section 3:Radio Communication Television Satellites – The satellite-reception dishes that you sometimes see in yards – Communications satellites use microwaves rather than the longer-wavelength radio waves used for normal television broadcasts. – Short wavelength microwaves travel more easily through the atmosphere. – The ground receiver dishes are rounded to focus the waves onto an antenna.

Section 3:Radio Communication The Global Positioning System – Helps lost hikers – GPS is a system of satellites, ground monitoring stations and receivers that determine your location. – Often four or five of the satellites are needed to show your location.