Radio historyRadio history

1906: On Christmas Eve, "Silent Night" via violin was the first US radio program of voice and music.

1888: Hertz detects radio waves.

1899: Marconi establishes first radio link between England and France.

1923: 500,000 radios are sold in U.S.

1926: The first radio jingle, for Wheaties.

1933: President Roosevelt lifts the nation’s spirit via his radio addresses

1939: WWII reports from war front are broadcast to US from London

1933: FCC created to regulate broadcasting

1938: “War of the Worlds” broadcast creates panic

To understand how radios work, you must first understand sound

waves!Radio waves, like sound waves, can be

described by their three properties-

Frequency,

Amplitude,

And

Wavelength

What is sound?

Mechanical energy that causes the particles of a medium to

vibrate back and forth

• Type of wave :– Longitudinal

•Energy travels withthe wave

• Sound cannot travel through space. Why?

no medium• Requires a medium:

– Solids, liquids and gases

Properties of a medium that affect speed

• Elastic (the ability to retain shape under stress)– More elastic the faster sound travels– Ex. Steel has a higher Elasticity then rubber; a solid

more elastic than liquid/gas– Temperature is an elastic property

• Higher temp, faster molecules, faster sound

• Inertial properties – (greater the inertia of molecules within a substance i.e

density, pressure the more difficult to move the molecules from original state)

– Ex. Sound travels faster in helium than air

Speed of sound-340 m/s in air

What is mach?

it is a term used to compare the speed of something to the speed of sound

mach 1- the speed of sound

mach 2- twice the speed of sound

Intensity (loudness)• Amount of energy in a sound wave – measured

in dB (decibles) • Determined by the amplitude

• High intensity- loud (lg. Amplitude)• Low intensity- soft (sm. Amplitude)

Pitch• How low or high the sound is

• Depends on frequency– High frequency- high pitch– Low frequency- low pitch

Frequency is the number of waves per second. It is measured in units called Hertz (Hz) after the man who first detected radio waves. Amplitude is one half the distance from the crest to the trough.

Frequency is the number of waves per second. It is measured in units called Hertz (Hz) after the man who first detected radio waves

High Frequency

Low Frequency

Medium Frequency

Infrasound and UltrasoundHumans can hear frequencies between 20Hz and 20,000Hz

Frequencies below 20Hz are Infrasound, while frequencies above 20,000Hz are Ultrasound

What’d you say?0 Hz 10 Hz 100 Hz 1,000 Hz 10,000 Hz 100,000 Hz

Bats hunt at night and can’t see their prey. What advantage does being able to hear ultrasonic frequencies give bats?

Elephants travel in large herds and seeing the leader of the group isn’t always possible. What advantage does being able to hear infrasonic frequencies give elephants?

Human

Bat

Elephant

Dog

How do we produce sound from an electric pulse?

• Transducer: converts energy from one form to another

What are some examples of transducers?

Electromagnetic:

• Antenna - converts electromagnetic waves into electric current and vice versa.

• Cathode ray tube (CRT) - converts electrical signals into visual form

• Fluorescent lamp, light bulb - converts electrical power into visible light

• Photodetector or Photoresistor (LDR) - converts changes in light levels into resistance changes

Electroacoustic:

Loudspeaker, earphone - converts electrical signals into sound (amplified signal → magnetic field → motion → air pressure)Microphone - converts sound into an electrical signal (air pressure → motion of conductor/coil → magnetic field → signal)Pick up (music technology) - converts motion of metal strings into an electrical signal (magnetism → electricity (signal))Hydrophone - converts changes in water pressure into an electrical formSonar transponder (water pressure → motion of conductor/coil → magnetic field → signal)

Doppler Effect

• A change in frequency (pitch) due to the motion of either the source or the observer

Doppler EffectStationary

Sonic Boom

• The shock wave produced due to speed of a plane breaking the sound barrier

• Usually 2 thumps (front and tail)• http://umscitech.wikispaces.com/file/view/E-

Chuck+Yeager+Broke+Sound+Barrier+60+Years+Ago+-+VOA+Story.mov

SONARSOund Navigation And Ranging

• is a technique that uses sound waves in a medium to navigate or to detect other objects with a transponder.

Now how are radio waves sent?• Check out this site :

http://www.pbs.org/wgbh/aso/tryit/radio/#