CHAPTER 3 : THE ELECTROMAGNETIC

SPECTRUM Section: 4: Wireless Communication

I. Radio and Television: Have you ever wondered how these programs reach you?

A. Transmission antennas send out, or broadcast, radio waves in

all directions. Radio waves carry information from the

antenna of a broadcasting station to the receiving antenna of

your radio or television.

1. two methods to transmit the signals.

a. Amplitude modulation

b. Frequency modulation

2. Radio stations broadcast using either method

3. TV stations use AM for pictures and FM for sound

4. Amplitude modulation (AM) – is a method of transmitting signals

by changing the amplitude of a wave.

a. Sound is converted in electronic signals at an broadcasting

station

b. These signals are converted into a pattern of changes in the

amplitude of a radio wave.

c. have long wavelengths

d. Reflected by ionoshpere

e. Broadcast over long

distances

5. Frequency Modulation (FM)- is a method of transmitting signals

by changing the frequency of a wave.

a. Travel as changes, or modulations, in the frequency of a wave.

b. Amplitude of the wave remains constant

c. Have higher energy and frequencies than AM waves

d. Pass through the ionosphere instead of being reflected back

e. Do not travels as far as AM waves

f. Produce better sound quality

6. The Radio Spectrum-

A. Used by:

1. taxi drivers, firefighters, and police officers

B. FCC assigns different radio frequencies for different

uses

1. AM stations use kilohertz (kHz), 535-1605 kHz

2. FM stations use megahertz (MHz), 88-108MHz

a. Hertz = 1 cycle/second

3. TV stations uses 2 sets of frequencies

a. VHF (very high frequency) 54-216 MHz

b. UHF (ultra high frequency) 470-806 MHz

II. Cellular Phones

A. Cellular phones transmit and receive signals using high-

frequency microwaves.

1. cellular phones work only when near a cellular

system

2. cellular system = regions divided into many

small cells, or geographical areas

3. cell phone sends out microwaves

4. tower picks up the microwaves and sends

it to a hub.

4. hub sends it to a receiver

5. receiver to a receiving cell phone

II. Communications Satellites

A. Communications satellites receive radio, television, and

telephone signals and relay the signals back to receivers on

Earth.

1. multiple satellites needed bc a satellite can only

“see” part of Earth at any given time

B. Satellite Phone Systems –

1. radio waves from one phone are sent to a

communicating satellite, which sends it to a

receiving phone.

2. results in being able to call from anywhere in

the world (cost is greater)

C. Television Satellites

1. both TV networks and cable companies use communication

satellites.

a. 1st TV signal changed into AM or FM waves

b. waves sent to satellite

c. Signals relayed to local stations around the world

2. Age of satellite Dishes

a. First dishes were very large

b. current dishes are much smaller

c. TV signals from satellites often are scrambled

to make sure that only people who pay for the

programs can use the signal. (use a decoding box)

D. Global Positioning System (GPS)

1. GPS- is a system of navigation originally designed for the military.

a. Uses a network of satellites that broadcast radio signals to

Earth.

b. Signals carry info that tells you your exact location on Earth’s

surface or in the air.

2. Commonly used in phones, cars, boats, airplanes, etc…