Radio WavesRadio Waves

Electromagnetic RadiationElectromagnetic Radiation

Radio Transmission and ReceptionRadio Transmission and Reception

Modulation TechniquesModulation Techniques

Spring 2006

UCSD Physics 8 2006

2

ElectromagnetismElectromagnetism

bull Electricity and magnetism are different facets of Electricity and magnetism are different facets of electromagnetismelectromagnetismndash recall that a static distribution of charges produces an electric fieldndash charges in motion (an electrical current) produce a magnetic fieldndash a changing magnetic field produces an electric field moving

charges

bull Electric and Magnetic fields produce forces on chargesElectric and Magnetic fields produce forces on chargesbull An An acceleratingaccelerating charge produces electromagnetic waves charge produces electromagnetic waves

(radiation)(radiation)bull Both electric and magnetic fields can transport energyBoth electric and magnetic fields can transport energy

ndash Electric field energy used in electrical circuits amp released in lightning

ndash Magnetic field carries energy through transformer

Spring 2006

UCSD Physics 8 2006

3

Electromagnetic RadiationElectromagnetic Radiation

bull Interrelated electric and magnetic fields traveling through Interrelated electric and magnetic fields traveling through spacespace

bull All electromagnetic radiation travels at All electromagnetic radiation travels at cc = 3 = 3101088 ms ms in in vacuum ndash vacuum ndash thethe cosmic speed limit cosmic speed limitndash real number is 2997924580 ms exactly

Spring 2006

UCSD Physics 8 2006

4

Examples of Electromagnetic RadiationExamples of Electromagnetic Radiation

bull AM and FM radio waves (including TV signals)AM and FM radio waves (including TV signals)bull Cell phone communication linksCell phone communication linksbull MicrowavesMicrowavesbull Infrared radiationInfrared radiationbull Light Light bull X-raysX-raysbull Gamma raysGamma raysbull What distinguishes these from one anotherWhat distinguishes these from one another

Spring 2006

UCSD Physics 8 2006

5

Wavelength (Frequency)Wavelength (Frequency)

Spring 2006

UCSD Physics 8 2006

6

The Electromagnetic SpectrumThe Electromagnetic Spectrum

bull Relationship between Relationship between frequencyfrequency speedspeed and and wavelengthwavelength

f f = = cc ff is is frequencyfrequency is is wavelengthwavelength cc is is speed of lightspeed of lightbull Different frequencies of electromagnetic radiation are Different frequencies of electromagnetic radiation are

better suited to different purposesbetter suited to different purposesbull The frequency of a radio wave determines its The frequency of a radio wave determines its

propagation characteristics through various mediapropagation characteristics through various media

Spring 2006

UCSD Physics 8 2006

7

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

Spring 2006

UCSD Physics 8 2006

8

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

Spring 2006

UCSD Physics 8 2006

9

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

Spring 2006

UCSD Physics 8 2006

10

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimum antenna length is 4 one-quarter wavelength

Spring 2006

UCSD Physics 8 2006

11

Encoding Information on Radio WavesEncoding Information on Radio Waves

bull What quantities characterize a radio waveWhat quantities characterize a radio wavebull Two common ways to carry analog information with Two common ways to carry analog information with

radio wavesradio wavesndash Amplitude Modulation (AM)ndash Frequency Modulation (FM) ldquostatic freerdquo

Spring 2006

UCSD Physics 8 2006

12

AM RadioAM Radiobull Amplitude Modulation (AM) uses changes in the Amplitude Modulation (AM) uses changes in the

signal signal strengthstrength to convey information to convey information

pressure modulation (sound)

electromagnetic wave modulation

Spring 2006

UCSD Physics 8 2006

13

AM Radio in PracticeAM Radio in Practice

bull Uses frequency range from 530 kHz to 1700 kHzUses frequency range from 530 kHz to 1700 kHzndash each station uses 9 kHzndash spacing is 10 kHz (a little breathing room) 117 channelsndash 9 kHz of bandwidth means 45 kHz is highest audio

frequency that can be encodedbull falls short of 20 kHz capability of human ear

bull Previous diagram is exaggeratedPrevious diagram is exaggeratedndash audio signal changes slowly with respect to radio carrier

bull typical speech sound of 500 Hz varies 1000 times slower than carrier

bull thus will see 1000 cycles of carrier to every one cycle of audio

Spring 2006

UCSD Physics 8 2006

14

FM RadioFM Radiobull Frequency Modulation (FM) uses changes in the Frequency Modulation (FM) uses changes in the

waversquos waversquos frequencyfrequency to convey information to convey information

pressure modulation (sound)

electromagnetic wavemodulation

Spring 2006

UCSD Physics 8 2006

15

FM Radio in PracticeFM Radio in Practicebull Spans 878 MHz to 1080 MHz in 200 kHz intervalsSpans 878 MHz to 1080 MHz in 200 kHz intervals

ndash 101 possible stationsndash example 91X runs from 910ndash912 MHz (centered at 911)

bull Nominally uses 150 kHz around centerNominally uses 150 kHz around centerndash 75 kHz on each sidendash 30 kHz for L + R (mono) 15 kHz audio capabilityndash 30 kHz offset for stereo difference signal (L - R)

bull Again figure exaggeratedAgain figure exaggeratedndash 75 kHz from band center modulation is gt 1000 times slower

than carrier so many cycles go by before frequency noticeably changes

Spring 2006

UCSD Physics 8 2006

16

AM vs FMAM vs FM

bull FM is not inherently higher frequency than AMFM is not inherently higher frequency than AMndash these are just choicesndash aviation band is 108ndash136 MHz uses AM technique

bull Besides the greater bandwidth (leading to stereo and Besides the greater bandwidth (leading to stereo and higher audio frequencies) FM is superior in immunity higher audio frequencies) FM is superior in immunity to environmental influencesto environmental influencesndash there are lots of ways to mess with an EM-waversquos amplitude

bull pass under a bridge

bull re-orient the antenna

ndash no natural processes mess with the frequencybull FM still works in the face of amplitude foolery

Spring 2006

UCSD Physics 8 2006

17

Frequency AllocationFrequency Allocation

Spring 2006

UCSD Physics 8 2006

18

Converting back to sound AMConverting back to sound AM

bull AM is easy just pass the AC signal from the antenna AM is easy just pass the AC signal from the antenna into a diodeinto a diodendash or better yet a diode bridgendash then use capacitor to smooth out bumps

bull but not so much as to smooth out audio bumps

B

D

radio signal

amplifierspeaker

Spring 2006

UCSD Physics 8 2006

19

Converting back to sound FMConverting back to sound FM

bull More sophisticatedMore sophisticatedndash need to compare instantaneous frequency to that of a

reference sourcendash then produce a voltage proportional to the differencendash Compute L = [(L+R) + (L-R)]2 R = [(L+R) - (L-R)]2ndash amplify the L and R voltages to send to speakers

bull Amplification is common to both schemesAmplification is common to both schemesndash intrinsic signal is far too weak to drive speaker

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments

Spring 2006

UCSD Physics 8 2006

2

ElectromagnetismElectromagnetism

bull Electricity and magnetism are different facets of Electricity and magnetism are different facets of electromagnetismelectromagnetismndash recall that a static distribution of charges produces an electric fieldndash charges in motion (an electrical current) produce a magnetic fieldndash a changing magnetic field produces an electric field moving

charges

bull Electric and Magnetic fields produce forces on chargesElectric and Magnetic fields produce forces on chargesbull An An acceleratingaccelerating charge produces electromagnetic waves charge produces electromagnetic waves

(radiation)(radiation)bull Both electric and magnetic fields can transport energyBoth electric and magnetic fields can transport energy

ndash Electric field energy used in electrical circuits amp released in lightning

ndash Magnetic field carries energy through transformer

Spring 2006

UCSD Physics 8 2006

3

Electromagnetic RadiationElectromagnetic Radiation

bull Interrelated electric and magnetic fields traveling through Interrelated electric and magnetic fields traveling through spacespace

bull All electromagnetic radiation travels at All electromagnetic radiation travels at cc = 3 = 3101088 ms ms in in vacuum ndash vacuum ndash thethe cosmic speed limit cosmic speed limitndash real number is 2997924580 ms exactly

Spring 2006

UCSD Physics 8 2006

4

Examples of Electromagnetic RadiationExamples of Electromagnetic Radiation

bull AM and FM radio waves (including TV signals)AM and FM radio waves (including TV signals)bull Cell phone communication linksCell phone communication linksbull MicrowavesMicrowavesbull Infrared radiationInfrared radiationbull Light Light bull X-raysX-raysbull Gamma raysGamma raysbull What distinguishes these from one anotherWhat distinguishes these from one another

Spring 2006

UCSD Physics 8 2006

5

Wavelength (Frequency)Wavelength (Frequency)

Spring 2006

UCSD Physics 8 2006

6

The Electromagnetic SpectrumThe Electromagnetic Spectrum

bull Relationship between Relationship between frequencyfrequency speedspeed and and wavelengthwavelength

f f = = cc ff is is frequencyfrequency is is wavelengthwavelength cc is is speed of lightspeed of lightbull Different frequencies of electromagnetic radiation are Different frequencies of electromagnetic radiation are

better suited to different purposesbetter suited to different purposesbull The frequency of a radio wave determines its The frequency of a radio wave determines its

propagation characteristics through various mediapropagation characteristics through various media

Spring 2006

UCSD Physics 8 2006

7

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

Spring 2006

UCSD Physics 8 2006

8

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

Spring 2006

UCSD Physics 8 2006

9

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

Spring 2006

UCSD Physics 8 2006

10

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimum antenna length is 4 one-quarter wavelength

Spring 2006

UCSD Physics 8 2006

11

Encoding Information on Radio WavesEncoding Information on Radio Waves

bull What quantities characterize a radio waveWhat quantities characterize a radio wavebull Two common ways to carry analog information with Two common ways to carry analog information with

radio wavesradio wavesndash Amplitude Modulation (AM)ndash Frequency Modulation (FM) ldquostatic freerdquo

Spring 2006

UCSD Physics 8 2006

12

AM RadioAM Radiobull Amplitude Modulation (AM) uses changes in the Amplitude Modulation (AM) uses changes in the

signal signal strengthstrength to convey information to convey information

pressure modulation (sound)

electromagnetic wave modulation

Spring 2006

UCSD Physics 8 2006

13

AM Radio in PracticeAM Radio in Practice

bull Uses frequency range from 530 kHz to 1700 kHzUses frequency range from 530 kHz to 1700 kHzndash each station uses 9 kHzndash spacing is 10 kHz (a little breathing room) 117 channelsndash 9 kHz of bandwidth means 45 kHz is highest audio

frequency that can be encodedbull falls short of 20 kHz capability of human ear

bull Previous diagram is exaggeratedPrevious diagram is exaggeratedndash audio signal changes slowly with respect to radio carrier

bull typical speech sound of 500 Hz varies 1000 times slower than carrier

bull thus will see 1000 cycles of carrier to every one cycle of audio

Spring 2006

UCSD Physics 8 2006

14

FM RadioFM Radiobull Frequency Modulation (FM) uses changes in the Frequency Modulation (FM) uses changes in the

waversquos waversquos frequencyfrequency to convey information to convey information

pressure modulation (sound)

electromagnetic wavemodulation

Spring 2006

UCSD Physics 8 2006

15

FM Radio in PracticeFM Radio in Practicebull Spans 878 MHz to 1080 MHz in 200 kHz intervalsSpans 878 MHz to 1080 MHz in 200 kHz intervals

ndash 101 possible stationsndash example 91X runs from 910ndash912 MHz (centered at 911)

bull Nominally uses 150 kHz around centerNominally uses 150 kHz around centerndash 75 kHz on each sidendash 30 kHz for L + R (mono) 15 kHz audio capabilityndash 30 kHz offset for stereo difference signal (L - R)

bull Again figure exaggeratedAgain figure exaggeratedndash 75 kHz from band center modulation is gt 1000 times slower

than carrier so many cycles go by before frequency noticeably changes

Spring 2006

UCSD Physics 8 2006

16

AM vs FMAM vs FM

bull FM is not inherently higher frequency than AMFM is not inherently higher frequency than AMndash these are just choicesndash aviation band is 108ndash136 MHz uses AM technique

bull Besides the greater bandwidth (leading to stereo and Besides the greater bandwidth (leading to stereo and higher audio frequencies) FM is superior in immunity higher audio frequencies) FM is superior in immunity to environmental influencesto environmental influencesndash there are lots of ways to mess with an EM-waversquos amplitude

bull pass under a bridge

bull re-orient the antenna

ndash no natural processes mess with the frequencybull FM still works in the face of amplitude foolery

Spring 2006

UCSD Physics 8 2006

17

Frequency AllocationFrequency Allocation

Spring 2006

UCSD Physics 8 2006

18

Converting back to sound AMConverting back to sound AM

bull AM is easy just pass the AC signal from the antenna AM is easy just pass the AC signal from the antenna into a diodeinto a diodendash or better yet a diode bridgendash then use capacitor to smooth out bumps

bull but not so much as to smooth out audio bumps

B

D

radio signal

amplifierspeaker

Spring 2006

UCSD Physics 8 2006

19

Converting back to sound FMConverting back to sound FM

bull More sophisticatedMore sophisticatedndash need to compare instantaneous frequency to that of a

reference sourcendash then produce a voltage proportional to the differencendash Compute L = [(L+R) + (L-R)]2 R = [(L+R) - (L-R)]2ndash amplify the L and R voltages to send to speakers

bull Amplification is common to both schemesAmplification is common to both schemesndash intrinsic signal is far too weak to drive speaker

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments

Spring 2006

UCSD Physics 8 2006

3

Electromagnetic RadiationElectromagnetic Radiation

bull Interrelated electric and magnetic fields traveling through Interrelated electric and magnetic fields traveling through spacespace

bull All electromagnetic radiation travels at All electromagnetic radiation travels at cc = 3 = 3101088 ms ms in in vacuum ndash vacuum ndash thethe cosmic speed limit cosmic speed limitndash real number is 2997924580 ms exactly

Spring 2006

UCSD Physics 8 2006

4

Examples of Electromagnetic RadiationExamples of Electromagnetic Radiation

bull AM and FM radio waves (including TV signals)AM and FM radio waves (including TV signals)bull Cell phone communication linksCell phone communication linksbull MicrowavesMicrowavesbull Infrared radiationInfrared radiationbull Light Light bull X-raysX-raysbull Gamma raysGamma raysbull What distinguishes these from one anotherWhat distinguishes these from one another

Spring 2006

UCSD Physics 8 2006

5

Wavelength (Frequency)Wavelength (Frequency)

Spring 2006

UCSD Physics 8 2006

6

The Electromagnetic SpectrumThe Electromagnetic Spectrum

bull Relationship between Relationship between frequencyfrequency speedspeed and and wavelengthwavelength

f f = = cc ff is is frequencyfrequency is is wavelengthwavelength cc is is speed of lightspeed of lightbull Different frequencies of electromagnetic radiation are Different frequencies of electromagnetic radiation are

better suited to different purposesbetter suited to different purposesbull The frequency of a radio wave determines its The frequency of a radio wave determines its

propagation characteristics through various mediapropagation characteristics through various media

Spring 2006

UCSD Physics 8 2006

7

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

Spring 2006

UCSD Physics 8 2006

8

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

Spring 2006

UCSD Physics 8 2006

9

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

Spring 2006

UCSD Physics 8 2006

10

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimum antenna length is 4 one-quarter wavelength

Spring 2006

UCSD Physics 8 2006

11

Encoding Information on Radio WavesEncoding Information on Radio Waves

bull What quantities characterize a radio waveWhat quantities characterize a radio wavebull Two common ways to carry analog information with Two common ways to carry analog information with

radio wavesradio wavesndash Amplitude Modulation (AM)ndash Frequency Modulation (FM) ldquostatic freerdquo

Spring 2006

UCSD Physics 8 2006

12

AM RadioAM Radiobull Amplitude Modulation (AM) uses changes in the Amplitude Modulation (AM) uses changes in the

signal signal strengthstrength to convey information to convey information

pressure modulation (sound)

electromagnetic wave modulation

Spring 2006

UCSD Physics 8 2006

13

AM Radio in PracticeAM Radio in Practice

bull Uses frequency range from 530 kHz to 1700 kHzUses frequency range from 530 kHz to 1700 kHzndash each station uses 9 kHzndash spacing is 10 kHz (a little breathing room) 117 channelsndash 9 kHz of bandwidth means 45 kHz is highest audio

frequency that can be encodedbull falls short of 20 kHz capability of human ear

bull Previous diagram is exaggeratedPrevious diagram is exaggeratedndash audio signal changes slowly with respect to radio carrier

bull typical speech sound of 500 Hz varies 1000 times slower than carrier

bull thus will see 1000 cycles of carrier to every one cycle of audio

Spring 2006

UCSD Physics 8 2006

14

FM RadioFM Radiobull Frequency Modulation (FM) uses changes in the Frequency Modulation (FM) uses changes in the

waversquos waversquos frequencyfrequency to convey information to convey information

pressure modulation (sound)

electromagnetic wavemodulation

Spring 2006

UCSD Physics 8 2006

15

FM Radio in PracticeFM Radio in Practicebull Spans 878 MHz to 1080 MHz in 200 kHz intervalsSpans 878 MHz to 1080 MHz in 200 kHz intervals

ndash 101 possible stationsndash example 91X runs from 910ndash912 MHz (centered at 911)

bull Nominally uses 150 kHz around centerNominally uses 150 kHz around centerndash 75 kHz on each sidendash 30 kHz for L + R (mono) 15 kHz audio capabilityndash 30 kHz offset for stereo difference signal (L - R)

bull Again figure exaggeratedAgain figure exaggeratedndash 75 kHz from band center modulation is gt 1000 times slower

than carrier so many cycles go by before frequency noticeably changes

Spring 2006

UCSD Physics 8 2006

16

AM vs FMAM vs FM

bull FM is not inherently higher frequency than AMFM is not inherently higher frequency than AMndash these are just choicesndash aviation band is 108ndash136 MHz uses AM technique

bull Besides the greater bandwidth (leading to stereo and Besides the greater bandwidth (leading to stereo and higher audio frequencies) FM is superior in immunity higher audio frequencies) FM is superior in immunity to environmental influencesto environmental influencesndash there are lots of ways to mess with an EM-waversquos amplitude

bull pass under a bridge

bull re-orient the antenna

ndash no natural processes mess with the frequencybull FM still works in the face of amplitude foolery

Spring 2006

UCSD Physics 8 2006

17

Frequency AllocationFrequency Allocation

Spring 2006

UCSD Physics 8 2006

18

Converting back to sound AMConverting back to sound AM

bull AM is easy just pass the AC signal from the antenna AM is easy just pass the AC signal from the antenna into a diodeinto a diodendash or better yet a diode bridgendash then use capacitor to smooth out bumps

bull but not so much as to smooth out audio bumps

B

D

radio signal

amplifierspeaker

Spring 2006

UCSD Physics 8 2006

19

Converting back to sound FMConverting back to sound FM

bull More sophisticatedMore sophisticatedndash need to compare instantaneous frequency to that of a

reference sourcendash then produce a voltage proportional to the differencendash Compute L = [(L+R) + (L-R)]2 R = [(L+R) - (L-R)]2ndash amplify the L and R voltages to send to speakers

bull Amplification is common to both schemesAmplification is common to both schemesndash intrinsic signal is far too weak to drive speaker

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments

Spring 2006

UCSD Physics 8 2006

4

Examples of Electromagnetic RadiationExamples of Electromagnetic Radiation

bull AM and FM radio waves (including TV signals)AM and FM radio waves (including TV signals)bull Cell phone communication linksCell phone communication linksbull MicrowavesMicrowavesbull Infrared radiationInfrared radiationbull Light Light bull X-raysX-raysbull Gamma raysGamma raysbull What distinguishes these from one anotherWhat distinguishes these from one another

Spring 2006

UCSD Physics 8 2006

5

Wavelength (Frequency)Wavelength (Frequency)

Spring 2006

UCSD Physics 8 2006

6

The Electromagnetic SpectrumThe Electromagnetic Spectrum

bull Relationship between Relationship between frequencyfrequency speedspeed and and wavelengthwavelength

f f = = cc ff is is frequencyfrequency is is wavelengthwavelength cc is is speed of lightspeed of lightbull Different frequencies of electromagnetic radiation are Different frequencies of electromagnetic radiation are

better suited to different purposesbetter suited to different purposesbull The frequency of a radio wave determines its The frequency of a radio wave determines its

propagation characteristics through various mediapropagation characteristics through various media

Spring 2006

UCSD Physics 8 2006

7

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

Spring 2006

UCSD Physics 8 2006

8

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

Spring 2006

UCSD Physics 8 2006

9

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

Spring 2006

UCSD Physics 8 2006

10

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimum antenna length is 4 one-quarter wavelength

Spring 2006

UCSD Physics 8 2006

11

Encoding Information on Radio WavesEncoding Information on Radio Waves

bull What quantities characterize a radio waveWhat quantities characterize a radio wavebull Two common ways to carry analog information with Two common ways to carry analog information with

radio wavesradio wavesndash Amplitude Modulation (AM)ndash Frequency Modulation (FM) ldquostatic freerdquo

Spring 2006

UCSD Physics 8 2006

12

AM RadioAM Radiobull Amplitude Modulation (AM) uses changes in the Amplitude Modulation (AM) uses changes in the

signal signal strengthstrength to convey information to convey information

pressure modulation (sound)

electromagnetic wave modulation

Spring 2006

UCSD Physics 8 2006

13

AM Radio in PracticeAM Radio in Practice

bull Uses frequency range from 530 kHz to 1700 kHzUses frequency range from 530 kHz to 1700 kHzndash each station uses 9 kHzndash spacing is 10 kHz (a little breathing room) 117 channelsndash 9 kHz of bandwidth means 45 kHz is highest audio

frequency that can be encodedbull falls short of 20 kHz capability of human ear

bull Previous diagram is exaggeratedPrevious diagram is exaggeratedndash audio signal changes slowly with respect to radio carrier

bull typical speech sound of 500 Hz varies 1000 times slower than carrier

bull thus will see 1000 cycles of carrier to every one cycle of audio

Spring 2006

UCSD Physics 8 2006

14

FM RadioFM Radiobull Frequency Modulation (FM) uses changes in the Frequency Modulation (FM) uses changes in the

waversquos waversquos frequencyfrequency to convey information to convey information

pressure modulation (sound)

electromagnetic wavemodulation

Spring 2006

UCSD Physics 8 2006

15

FM Radio in PracticeFM Radio in Practicebull Spans 878 MHz to 1080 MHz in 200 kHz intervalsSpans 878 MHz to 1080 MHz in 200 kHz intervals

ndash 101 possible stationsndash example 91X runs from 910ndash912 MHz (centered at 911)

bull Nominally uses 150 kHz around centerNominally uses 150 kHz around centerndash 75 kHz on each sidendash 30 kHz for L + R (mono) 15 kHz audio capabilityndash 30 kHz offset for stereo difference signal (L - R)

bull Again figure exaggeratedAgain figure exaggeratedndash 75 kHz from band center modulation is gt 1000 times slower

than carrier so many cycles go by before frequency noticeably changes

Spring 2006

UCSD Physics 8 2006

16

AM vs FMAM vs FM

bull FM is not inherently higher frequency than AMFM is not inherently higher frequency than AMndash these are just choicesndash aviation band is 108ndash136 MHz uses AM technique

bull Besides the greater bandwidth (leading to stereo and Besides the greater bandwidth (leading to stereo and higher audio frequencies) FM is superior in immunity higher audio frequencies) FM is superior in immunity to environmental influencesto environmental influencesndash there are lots of ways to mess with an EM-waversquos amplitude

bull pass under a bridge

bull re-orient the antenna

ndash no natural processes mess with the frequencybull FM still works in the face of amplitude foolery

Spring 2006

UCSD Physics 8 2006

17

Frequency AllocationFrequency Allocation

Spring 2006

UCSD Physics 8 2006

18

Converting back to sound AMConverting back to sound AM

bull AM is easy just pass the AC signal from the antenna AM is easy just pass the AC signal from the antenna into a diodeinto a diodendash or better yet a diode bridgendash then use capacitor to smooth out bumps

bull but not so much as to smooth out audio bumps

B

D

radio signal

amplifierspeaker

Spring 2006

UCSD Physics 8 2006

19

Converting back to sound FMConverting back to sound FM

bull More sophisticatedMore sophisticatedndash need to compare instantaneous frequency to that of a

reference sourcendash then produce a voltage proportional to the differencendash Compute L = [(L+R) + (L-R)]2 R = [(L+R) - (L-R)]2ndash amplify the L and R voltages to send to speakers

bull Amplification is common to both schemesAmplification is common to both schemesndash intrinsic signal is far too weak to drive speaker

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments

Spring 2006

UCSD Physics 8 2006

5

Wavelength (Frequency)Wavelength (Frequency)

Spring 2006

UCSD Physics 8 2006

6

The Electromagnetic SpectrumThe Electromagnetic Spectrum

bull Relationship between Relationship between frequencyfrequency speedspeed and and wavelengthwavelength

f f = = cc ff is is frequencyfrequency is is wavelengthwavelength cc is is speed of lightspeed of lightbull Different frequencies of electromagnetic radiation are Different frequencies of electromagnetic radiation are

better suited to different purposesbetter suited to different purposesbull The frequency of a radio wave determines its The frequency of a radio wave determines its

propagation characteristics through various mediapropagation characteristics through various media

Spring 2006

UCSD Physics 8 2006

7

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

Spring 2006

UCSD Physics 8 2006

8

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

Spring 2006

UCSD Physics 8 2006

9

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

Spring 2006

UCSD Physics 8 2006

10

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimum antenna length is 4 one-quarter wavelength

Spring 2006

UCSD Physics 8 2006

11

Encoding Information on Radio WavesEncoding Information on Radio Waves

bull What quantities characterize a radio waveWhat quantities characterize a radio wavebull Two common ways to carry analog information with Two common ways to carry analog information with

radio wavesradio wavesndash Amplitude Modulation (AM)ndash Frequency Modulation (FM) ldquostatic freerdquo

Spring 2006

UCSD Physics 8 2006

12

AM RadioAM Radiobull Amplitude Modulation (AM) uses changes in the Amplitude Modulation (AM) uses changes in the

signal signal strengthstrength to convey information to convey information

pressure modulation (sound)

electromagnetic wave modulation

Spring 2006

UCSD Physics 8 2006

13

AM Radio in PracticeAM Radio in Practice

bull Uses frequency range from 530 kHz to 1700 kHzUses frequency range from 530 kHz to 1700 kHzndash each station uses 9 kHzndash spacing is 10 kHz (a little breathing room) 117 channelsndash 9 kHz of bandwidth means 45 kHz is highest audio

frequency that can be encodedbull falls short of 20 kHz capability of human ear

bull Previous diagram is exaggeratedPrevious diagram is exaggeratedndash audio signal changes slowly with respect to radio carrier

bull typical speech sound of 500 Hz varies 1000 times slower than carrier

bull thus will see 1000 cycles of carrier to every one cycle of audio

Spring 2006

UCSD Physics 8 2006

14

FM RadioFM Radiobull Frequency Modulation (FM) uses changes in the Frequency Modulation (FM) uses changes in the

waversquos waversquos frequencyfrequency to convey information to convey information

pressure modulation (sound)

electromagnetic wavemodulation

Spring 2006

UCSD Physics 8 2006

15

FM Radio in PracticeFM Radio in Practicebull Spans 878 MHz to 1080 MHz in 200 kHz intervalsSpans 878 MHz to 1080 MHz in 200 kHz intervals

ndash 101 possible stationsndash example 91X runs from 910ndash912 MHz (centered at 911)

bull Nominally uses 150 kHz around centerNominally uses 150 kHz around centerndash 75 kHz on each sidendash 30 kHz for L + R (mono) 15 kHz audio capabilityndash 30 kHz offset for stereo difference signal (L - R)

bull Again figure exaggeratedAgain figure exaggeratedndash 75 kHz from band center modulation is gt 1000 times slower

than carrier so many cycles go by before frequency noticeably changes

Spring 2006

UCSD Physics 8 2006

16

AM vs FMAM vs FM

bull FM is not inherently higher frequency than AMFM is not inherently higher frequency than AMndash these are just choicesndash aviation band is 108ndash136 MHz uses AM technique

bull Besides the greater bandwidth (leading to stereo and Besides the greater bandwidth (leading to stereo and higher audio frequencies) FM is superior in immunity higher audio frequencies) FM is superior in immunity to environmental influencesto environmental influencesndash there are lots of ways to mess with an EM-waversquos amplitude

bull pass under a bridge

bull re-orient the antenna

ndash no natural processes mess with the frequencybull FM still works in the face of amplitude foolery

Spring 2006

UCSD Physics 8 2006

17

Frequency AllocationFrequency Allocation

Spring 2006

UCSD Physics 8 2006

18

Converting back to sound AMConverting back to sound AM

bull AM is easy just pass the AC signal from the antenna AM is easy just pass the AC signal from the antenna into a diodeinto a diodendash or better yet a diode bridgendash then use capacitor to smooth out bumps

bull but not so much as to smooth out audio bumps

B

D

radio signal

amplifierspeaker

Spring 2006

UCSD Physics 8 2006

19

Converting back to sound FMConverting back to sound FM

bull More sophisticatedMore sophisticatedndash need to compare instantaneous frequency to that of a

reference sourcendash then produce a voltage proportional to the differencendash Compute L = [(L+R) + (L-R)]2 R = [(L+R) - (L-R)]2ndash amplify the L and R voltages to send to speakers

bull Amplification is common to both schemesAmplification is common to both schemesndash intrinsic signal is far too weak to drive speaker

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments

Spring 2006

UCSD Physics 8 2006

6

The Electromagnetic SpectrumThe Electromagnetic Spectrum

bull Relationship between Relationship between frequencyfrequency speedspeed and and wavelengthwavelength

f f = = cc ff is is frequencyfrequency is is wavelengthwavelength cc is is speed of lightspeed of lightbull Different frequencies of electromagnetic radiation are Different frequencies of electromagnetic radiation are

better suited to different purposesbetter suited to different purposesbull The frequency of a radio wave determines its The frequency of a radio wave determines its

propagation characteristics through various mediapropagation characteristics through various media

Spring 2006

UCSD Physics 8 2006

7

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

Spring 2006

UCSD Physics 8 2006

8

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

Spring 2006

UCSD Physics 8 2006

9

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

Spring 2006

UCSD Physics 8 2006

10

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimum antenna length is 4 one-quarter wavelength

Spring 2006

UCSD Physics 8 2006

11

Encoding Information on Radio WavesEncoding Information on Radio Waves

bull What quantities characterize a radio waveWhat quantities characterize a radio wavebull Two common ways to carry analog information with Two common ways to carry analog information with

radio wavesradio wavesndash Amplitude Modulation (AM)ndash Frequency Modulation (FM) ldquostatic freerdquo

Spring 2006

UCSD Physics 8 2006

12

AM RadioAM Radiobull Amplitude Modulation (AM) uses changes in the Amplitude Modulation (AM) uses changes in the

signal signal strengthstrength to convey information to convey information

pressure modulation (sound)

electromagnetic wave modulation

Spring 2006

UCSD Physics 8 2006

13

AM Radio in PracticeAM Radio in Practice

bull Uses frequency range from 530 kHz to 1700 kHzUses frequency range from 530 kHz to 1700 kHzndash each station uses 9 kHzndash spacing is 10 kHz (a little breathing room) 117 channelsndash 9 kHz of bandwidth means 45 kHz is highest audio

frequency that can be encodedbull falls short of 20 kHz capability of human ear

bull Previous diagram is exaggeratedPrevious diagram is exaggeratedndash audio signal changes slowly with respect to radio carrier

bull typical speech sound of 500 Hz varies 1000 times slower than carrier

bull thus will see 1000 cycles of carrier to every one cycle of audio

Spring 2006

UCSD Physics 8 2006

14

FM RadioFM Radiobull Frequency Modulation (FM) uses changes in the Frequency Modulation (FM) uses changes in the

waversquos waversquos frequencyfrequency to convey information to convey information

pressure modulation (sound)

electromagnetic wavemodulation

Spring 2006

UCSD Physics 8 2006

15

FM Radio in PracticeFM Radio in Practicebull Spans 878 MHz to 1080 MHz in 200 kHz intervalsSpans 878 MHz to 1080 MHz in 200 kHz intervals

ndash 101 possible stationsndash example 91X runs from 910ndash912 MHz (centered at 911)

bull Nominally uses 150 kHz around centerNominally uses 150 kHz around centerndash 75 kHz on each sidendash 30 kHz for L + R (mono) 15 kHz audio capabilityndash 30 kHz offset for stereo difference signal (L - R)

bull Again figure exaggeratedAgain figure exaggeratedndash 75 kHz from band center modulation is gt 1000 times slower

than carrier so many cycles go by before frequency noticeably changes

Spring 2006

UCSD Physics 8 2006

16

AM vs FMAM vs FM

bull FM is not inherently higher frequency than AMFM is not inherently higher frequency than AMndash these are just choicesndash aviation band is 108ndash136 MHz uses AM technique

bull Besides the greater bandwidth (leading to stereo and Besides the greater bandwidth (leading to stereo and higher audio frequencies) FM is superior in immunity higher audio frequencies) FM is superior in immunity to environmental influencesto environmental influencesndash there are lots of ways to mess with an EM-waversquos amplitude

bull pass under a bridge

bull re-orient the antenna

ndash no natural processes mess with the frequencybull FM still works in the face of amplitude foolery

Spring 2006

UCSD Physics 8 2006

17

Frequency AllocationFrequency Allocation

Spring 2006

UCSD Physics 8 2006

18

Converting back to sound AMConverting back to sound AM

bull AM is easy just pass the AC signal from the antenna AM is easy just pass the AC signal from the antenna into a diodeinto a diodendash or better yet a diode bridgendash then use capacitor to smooth out bumps

bull but not so much as to smooth out audio bumps

B

D

radio signal

amplifierspeaker

Spring 2006

UCSD Physics 8 2006

19

Converting back to sound FMConverting back to sound FM

bull More sophisticatedMore sophisticatedndash need to compare instantaneous frequency to that of a

reference sourcendash then produce a voltage proportional to the differencendash Compute L = [(L+R) + (L-R)]2 R = [(L+R) - (L-R)]2ndash amplify the L and R voltages to send to speakers

bull Amplification is common to both schemesAmplification is common to both schemesndash intrinsic signal is far too weak to drive speaker

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments

Spring 2006

UCSD Physics 8 2006

7

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

Spring 2006

UCSD Physics 8 2006

8

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

Spring 2006

UCSD Physics 8 2006

9

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

Spring 2006

UCSD Physics 8 2006

10

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimum antenna length is 4 one-quarter wavelength

Spring 2006

UCSD Physics 8 2006

11

Encoding Information on Radio WavesEncoding Information on Radio Waves

bull What quantities characterize a radio waveWhat quantities characterize a radio wavebull Two common ways to carry analog information with Two common ways to carry analog information with

radio wavesradio wavesndash Amplitude Modulation (AM)ndash Frequency Modulation (FM) ldquostatic freerdquo

Spring 2006

UCSD Physics 8 2006

12

AM RadioAM Radiobull Amplitude Modulation (AM) uses changes in the Amplitude Modulation (AM) uses changes in the

signal signal strengthstrength to convey information to convey information

pressure modulation (sound)

electromagnetic wave modulation

Spring 2006

UCSD Physics 8 2006

13

AM Radio in PracticeAM Radio in Practice

bull Uses frequency range from 530 kHz to 1700 kHzUses frequency range from 530 kHz to 1700 kHzndash each station uses 9 kHzndash spacing is 10 kHz (a little breathing room) 117 channelsndash 9 kHz of bandwidth means 45 kHz is highest audio

frequency that can be encodedbull falls short of 20 kHz capability of human ear

bull Previous diagram is exaggeratedPrevious diagram is exaggeratedndash audio signal changes slowly with respect to radio carrier

bull typical speech sound of 500 Hz varies 1000 times slower than carrier

bull thus will see 1000 cycles of carrier to every one cycle of audio

Spring 2006

UCSD Physics 8 2006

14

FM RadioFM Radiobull Frequency Modulation (FM) uses changes in the Frequency Modulation (FM) uses changes in the

waversquos waversquos frequencyfrequency to convey information to convey information

pressure modulation (sound)

electromagnetic wavemodulation

Spring 2006

UCSD Physics 8 2006

15

FM Radio in PracticeFM Radio in Practicebull Spans 878 MHz to 1080 MHz in 200 kHz intervalsSpans 878 MHz to 1080 MHz in 200 kHz intervals

ndash 101 possible stationsndash example 91X runs from 910ndash912 MHz (centered at 911)

bull Nominally uses 150 kHz around centerNominally uses 150 kHz around centerndash 75 kHz on each sidendash 30 kHz for L + R (mono) 15 kHz audio capabilityndash 30 kHz offset for stereo difference signal (L - R)

bull Again figure exaggeratedAgain figure exaggeratedndash 75 kHz from band center modulation is gt 1000 times slower

than carrier so many cycles go by before frequency noticeably changes

Spring 2006

UCSD Physics 8 2006

16

AM vs FMAM vs FM

bull FM is not inherently higher frequency than AMFM is not inherently higher frequency than AMndash these are just choicesndash aviation band is 108ndash136 MHz uses AM technique

bull Besides the greater bandwidth (leading to stereo and Besides the greater bandwidth (leading to stereo and higher audio frequencies) FM is superior in immunity higher audio frequencies) FM is superior in immunity to environmental influencesto environmental influencesndash there are lots of ways to mess with an EM-waversquos amplitude

bull pass under a bridge

bull re-orient the antenna

ndash no natural processes mess with the frequencybull FM still works in the face of amplitude foolery

Spring 2006

UCSD Physics 8 2006

17

Frequency AllocationFrequency Allocation

Spring 2006

UCSD Physics 8 2006

18

Converting back to sound AMConverting back to sound AM

bull AM is easy just pass the AC signal from the antenna AM is easy just pass the AC signal from the antenna into a diodeinto a diodendash or better yet a diode bridgendash then use capacitor to smooth out bumps

bull but not so much as to smooth out audio bumps

B

D

radio signal

amplifierspeaker

Spring 2006

UCSD Physics 8 2006

19

Converting back to sound FMConverting back to sound FM

bull More sophisticatedMore sophisticatedndash need to compare instantaneous frequency to that of a

reference sourcendash then produce a voltage proportional to the differencendash Compute L = [(L+R) + (L-R)]2 R = [(L+R) - (L-R)]2ndash amplify the L and R voltages to send to speakers

bull Amplification is common to both schemesAmplification is common to both schemesndash intrinsic signal is far too weak to drive speaker

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments

Spring 2006

UCSD Physics 8 2006

8

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

Spring 2006

UCSD Physics 8 2006

9

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

Spring 2006

UCSD Physics 8 2006

10

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimum antenna length is 4 one-quarter wavelength

Spring 2006

UCSD Physics 8 2006

11

Encoding Information on Radio WavesEncoding Information on Radio Waves

bull What quantities characterize a radio waveWhat quantities characterize a radio wavebull Two common ways to carry analog information with Two common ways to carry analog information with

radio wavesradio wavesndash Amplitude Modulation (AM)ndash Frequency Modulation (FM) ldquostatic freerdquo

Spring 2006

UCSD Physics 8 2006

12

AM RadioAM Radiobull Amplitude Modulation (AM) uses changes in the Amplitude Modulation (AM) uses changes in the

signal signal strengthstrength to convey information to convey information

pressure modulation (sound)

electromagnetic wave modulation

Spring 2006

UCSD Physics 8 2006

13

AM Radio in PracticeAM Radio in Practice

bull Uses frequency range from 530 kHz to 1700 kHzUses frequency range from 530 kHz to 1700 kHzndash each station uses 9 kHzndash spacing is 10 kHz (a little breathing room) 117 channelsndash 9 kHz of bandwidth means 45 kHz is highest audio

frequency that can be encodedbull falls short of 20 kHz capability of human ear

bull Previous diagram is exaggeratedPrevious diagram is exaggeratedndash audio signal changes slowly with respect to radio carrier

bull typical speech sound of 500 Hz varies 1000 times slower than carrier

bull thus will see 1000 cycles of carrier to every one cycle of audio

Spring 2006

UCSD Physics 8 2006

14

FM RadioFM Radiobull Frequency Modulation (FM) uses changes in the Frequency Modulation (FM) uses changes in the

waversquos waversquos frequencyfrequency to convey information to convey information

pressure modulation (sound)

electromagnetic wavemodulation

Spring 2006

UCSD Physics 8 2006

15

FM Radio in PracticeFM Radio in Practicebull Spans 878 MHz to 1080 MHz in 200 kHz intervalsSpans 878 MHz to 1080 MHz in 200 kHz intervals

ndash 101 possible stationsndash example 91X runs from 910ndash912 MHz (centered at 911)

bull Nominally uses 150 kHz around centerNominally uses 150 kHz around centerndash 75 kHz on each sidendash 30 kHz for L + R (mono) 15 kHz audio capabilityndash 30 kHz offset for stereo difference signal (L - R)

bull Again figure exaggeratedAgain figure exaggeratedndash 75 kHz from band center modulation is gt 1000 times slower

than carrier so many cycles go by before frequency noticeably changes

Spring 2006

UCSD Physics 8 2006

16

AM vs FMAM vs FM

bull FM is not inherently higher frequency than AMFM is not inherently higher frequency than AMndash these are just choicesndash aviation band is 108ndash136 MHz uses AM technique

bull Besides the greater bandwidth (leading to stereo and Besides the greater bandwidth (leading to stereo and higher audio frequencies) FM is superior in immunity higher audio frequencies) FM is superior in immunity to environmental influencesto environmental influencesndash there are lots of ways to mess with an EM-waversquos amplitude

bull pass under a bridge

bull re-orient the antenna

ndash no natural processes mess with the frequencybull FM still works in the face of amplitude foolery

Spring 2006

UCSD Physics 8 2006

17

Frequency AllocationFrequency Allocation

Spring 2006

UCSD Physics 8 2006

18

Converting back to sound AMConverting back to sound AM

bull AM is easy just pass the AC signal from the antenna AM is easy just pass the AC signal from the antenna into a diodeinto a diodendash or better yet a diode bridgendash then use capacitor to smooth out bumps

bull but not so much as to smooth out audio bumps

B

D

radio signal

amplifierspeaker

Spring 2006

UCSD Physics 8 2006

19

Converting back to sound FMConverting back to sound FM

bull More sophisticatedMore sophisticatedndash need to compare instantaneous frequency to that of a

reference sourcendash then produce a voltage proportional to the differencendash Compute L = [(L+R) + (L-R)]2 R = [(L+R) - (L-R)]2ndash amplify the L and R voltages to send to speakers

bull Amplification is common to both schemesAmplification is common to both schemesndash intrinsic signal is far too weak to drive speaker

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments

Spring 2006

UCSD Physics 8 2006

9

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

Spring 2006

UCSD Physics 8 2006

10

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimum antenna length is 4 one-quarter wavelength

Spring 2006

UCSD Physics 8 2006

11

Encoding Information on Radio WavesEncoding Information on Radio Waves

bull What quantities characterize a radio waveWhat quantities characterize a radio wavebull Two common ways to carry analog information with Two common ways to carry analog information with

radio wavesradio wavesndash Amplitude Modulation (AM)ndash Frequency Modulation (FM) ldquostatic freerdquo

Spring 2006

UCSD Physics 8 2006

12

AM RadioAM Radiobull Amplitude Modulation (AM) uses changes in the Amplitude Modulation (AM) uses changes in the

signal signal strengthstrength to convey information to convey information

pressure modulation (sound)

electromagnetic wave modulation

Spring 2006

UCSD Physics 8 2006

13

AM Radio in PracticeAM Radio in Practice

bull Uses frequency range from 530 kHz to 1700 kHzUses frequency range from 530 kHz to 1700 kHzndash each station uses 9 kHzndash spacing is 10 kHz (a little breathing room) 117 channelsndash 9 kHz of bandwidth means 45 kHz is highest audio

frequency that can be encodedbull falls short of 20 kHz capability of human ear

bull Previous diagram is exaggeratedPrevious diagram is exaggeratedndash audio signal changes slowly with respect to radio carrier

bull typical speech sound of 500 Hz varies 1000 times slower than carrier

bull thus will see 1000 cycles of carrier to every one cycle of audio

Spring 2006

UCSD Physics 8 2006

14

FM RadioFM Radiobull Frequency Modulation (FM) uses changes in the Frequency Modulation (FM) uses changes in the

waversquos waversquos frequencyfrequency to convey information to convey information

pressure modulation (sound)

electromagnetic wavemodulation

Spring 2006

UCSD Physics 8 2006

15

FM Radio in PracticeFM Radio in Practicebull Spans 878 MHz to 1080 MHz in 200 kHz intervalsSpans 878 MHz to 1080 MHz in 200 kHz intervals

ndash 101 possible stationsndash example 91X runs from 910ndash912 MHz (centered at 911)

bull Nominally uses 150 kHz around centerNominally uses 150 kHz around centerndash 75 kHz on each sidendash 30 kHz for L + R (mono) 15 kHz audio capabilityndash 30 kHz offset for stereo difference signal (L - R)

bull Again figure exaggeratedAgain figure exaggeratedndash 75 kHz from band center modulation is gt 1000 times slower

than carrier so many cycles go by before frequency noticeably changes

Spring 2006

UCSD Physics 8 2006

16

AM vs FMAM vs FM

bull FM is not inherently higher frequency than AMFM is not inherently higher frequency than AMndash these are just choicesndash aviation band is 108ndash136 MHz uses AM technique

bull Besides the greater bandwidth (leading to stereo and Besides the greater bandwidth (leading to stereo and higher audio frequencies) FM is superior in immunity higher audio frequencies) FM is superior in immunity to environmental influencesto environmental influencesndash there are lots of ways to mess with an EM-waversquos amplitude

bull pass under a bridge

bull re-orient the antenna

ndash no natural processes mess with the frequencybull FM still works in the face of amplitude foolery

Spring 2006

UCSD Physics 8 2006

17

Frequency AllocationFrequency Allocation

Spring 2006

UCSD Physics 8 2006

18

Converting back to sound AMConverting back to sound AM

bull AM is easy just pass the AC signal from the antenna AM is easy just pass the AC signal from the antenna into a diodeinto a diodendash or better yet a diode bridgendash then use capacitor to smooth out bumps

bull but not so much as to smooth out audio bumps

B

D

radio signal

amplifierspeaker

Spring 2006

UCSD Physics 8 2006

19

Converting back to sound FMConverting back to sound FM

bull More sophisticatedMore sophisticatedndash need to compare instantaneous frequency to that of a

reference sourcendash then produce a voltage proportional to the differencendash Compute L = [(L+R) + (L-R)]2 R = [(L+R) - (L-R)]2ndash amplify the L and R voltages to send to speakers

bull Amplification is common to both schemesAmplification is common to both schemesndash intrinsic signal is far too weak to drive speaker

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments

Spring 2006

UCSD Physics 8 2006

10

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimum antenna length is 4 one-quarter wavelength

Spring 2006

UCSD Physics 8 2006

11

Encoding Information on Radio WavesEncoding Information on Radio Waves

bull What quantities characterize a radio waveWhat quantities characterize a radio wavebull Two common ways to carry analog information with Two common ways to carry analog information with

radio wavesradio wavesndash Amplitude Modulation (AM)ndash Frequency Modulation (FM) ldquostatic freerdquo

Spring 2006

UCSD Physics 8 2006

12

AM RadioAM Radiobull Amplitude Modulation (AM) uses changes in the Amplitude Modulation (AM) uses changes in the

signal signal strengthstrength to convey information to convey information

pressure modulation (sound)

electromagnetic wave modulation

Spring 2006

UCSD Physics 8 2006

13

AM Radio in PracticeAM Radio in Practice

bull Uses frequency range from 530 kHz to 1700 kHzUses frequency range from 530 kHz to 1700 kHzndash each station uses 9 kHzndash spacing is 10 kHz (a little breathing room) 117 channelsndash 9 kHz of bandwidth means 45 kHz is highest audio

frequency that can be encodedbull falls short of 20 kHz capability of human ear

bull Previous diagram is exaggeratedPrevious diagram is exaggeratedndash audio signal changes slowly with respect to radio carrier

bull typical speech sound of 500 Hz varies 1000 times slower than carrier

bull thus will see 1000 cycles of carrier to every one cycle of audio

Spring 2006

UCSD Physics 8 2006

14

FM RadioFM Radiobull Frequency Modulation (FM) uses changes in the Frequency Modulation (FM) uses changes in the

waversquos waversquos frequencyfrequency to convey information to convey information

pressure modulation (sound)

electromagnetic wavemodulation

Spring 2006

UCSD Physics 8 2006

15

FM Radio in PracticeFM Radio in Practicebull Spans 878 MHz to 1080 MHz in 200 kHz intervalsSpans 878 MHz to 1080 MHz in 200 kHz intervals

ndash 101 possible stationsndash example 91X runs from 910ndash912 MHz (centered at 911)

bull Nominally uses 150 kHz around centerNominally uses 150 kHz around centerndash 75 kHz on each sidendash 30 kHz for L + R (mono) 15 kHz audio capabilityndash 30 kHz offset for stereo difference signal (L - R)

bull Again figure exaggeratedAgain figure exaggeratedndash 75 kHz from band center modulation is gt 1000 times slower

than carrier so many cycles go by before frequency noticeably changes

Spring 2006

UCSD Physics 8 2006

16

AM vs FMAM vs FM

bull FM is not inherently higher frequency than AMFM is not inherently higher frequency than AMndash these are just choicesndash aviation band is 108ndash136 MHz uses AM technique

bull Besides the greater bandwidth (leading to stereo and Besides the greater bandwidth (leading to stereo and higher audio frequencies) FM is superior in immunity higher audio frequencies) FM is superior in immunity to environmental influencesto environmental influencesndash there are lots of ways to mess with an EM-waversquos amplitude

bull pass under a bridge

bull re-orient the antenna

ndash no natural processes mess with the frequencybull FM still works in the face of amplitude foolery

Spring 2006

UCSD Physics 8 2006

17

Frequency AllocationFrequency Allocation

Spring 2006

UCSD Physics 8 2006

18

Converting back to sound AMConverting back to sound AM

bull AM is easy just pass the AC signal from the antenna AM is easy just pass the AC signal from the antenna into a diodeinto a diodendash or better yet a diode bridgendash then use capacitor to smooth out bumps

bull but not so much as to smooth out audio bumps

B

D

radio signal

amplifierspeaker

Spring 2006

UCSD Physics 8 2006

19

Converting back to sound FMConverting back to sound FM

bull More sophisticatedMore sophisticatedndash need to compare instantaneous frequency to that of a

reference sourcendash then produce a voltage proportional to the differencendash Compute L = [(L+R) + (L-R)]2 R = [(L+R) - (L-R)]2ndash amplify the L and R voltages to send to speakers

bull Amplification is common to both schemesAmplification is common to both schemesndash intrinsic signal is far too weak to drive speaker

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments

Spring 2006

UCSD Physics 8 2006

11

Encoding Information on Radio WavesEncoding Information on Radio Waves

bull What quantities characterize a radio waveWhat quantities characterize a radio wavebull Two common ways to carry analog information with Two common ways to carry analog information with

radio wavesradio wavesndash Amplitude Modulation (AM)ndash Frequency Modulation (FM) ldquostatic freerdquo

Spring 2006

UCSD Physics 8 2006

12

AM RadioAM Radiobull Amplitude Modulation (AM) uses changes in the Amplitude Modulation (AM) uses changes in the

signal signal strengthstrength to convey information to convey information

pressure modulation (sound)

electromagnetic wave modulation

Spring 2006

UCSD Physics 8 2006

13

AM Radio in PracticeAM Radio in Practice

bull Uses frequency range from 530 kHz to 1700 kHzUses frequency range from 530 kHz to 1700 kHzndash each station uses 9 kHzndash spacing is 10 kHz (a little breathing room) 117 channelsndash 9 kHz of bandwidth means 45 kHz is highest audio

frequency that can be encodedbull falls short of 20 kHz capability of human ear

bull Previous diagram is exaggeratedPrevious diagram is exaggeratedndash audio signal changes slowly with respect to radio carrier

bull typical speech sound of 500 Hz varies 1000 times slower than carrier

bull thus will see 1000 cycles of carrier to every one cycle of audio

Spring 2006

UCSD Physics 8 2006

14

FM RadioFM Radiobull Frequency Modulation (FM) uses changes in the Frequency Modulation (FM) uses changes in the

waversquos waversquos frequencyfrequency to convey information to convey information

pressure modulation (sound)

electromagnetic wavemodulation

Spring 2006

UCSD Physics 8 2006

15

FM Radio in PracticeFM Radio in Practicebull Spans 878 MHz to 1080 MHz in 200 kHz intervalsSpans 878 MHz to 1080 MHz in 200 kHz intervals

ndash 101 possible stationsndash example 91X runs from 910ndash912 MHz (centered at 911)

bull Nominally uses 150 kHz around centerNominally uses 150 kHz around centerndash 75 kHz on each sidendash 30 kHz for L + R (mono) 15 kHz audio capabilityndash 30 kHz offset for stereo difference signal (L - R)

bull Again figure exaggeratedAgain figure exaggeratedndash 75 kHz from band center modulation is gt 1000 times slower

than carrier so many cycles go by before frequency noticeably changes

Spring 2006

UCSD Physics 8 2006

16

AM vs FMAM vs FM

bull FM is not inherently higher frequency than AMFM is not inherently higher frequency than AMndash these are just choicesndash aviation band is 108ndash136 MHz uses AM technique

bull Besides the greater bandwidth (leading to stereo and Besides the greater bandwidth (leading to stereo and higher audio frequencies) FM is superior in immunity higher audio frequencies) FM is superior in immunity to environmental influencesto environmental influencesndash there are lots of ways to mess with an EM-waversquos amplitude

bull pass under a bridge

bull re-orient the antenna

ndash no natural processes mess with the frequencybull FM still works in the face of amplitude foolery

Spring 2006

UCSD Physics 8 2006

17

Frequency AllocationFrequency Allocation

Spring 2006

UCSD Physics 8 2006

18

Converting back to sound AMConverting back to sound AM

bull AM is easy just pass the AC signal from the antenna AM is easy just pass the AC signal from the antenna into a diodeinto a diodendash or better yet a diode bridgendash then use capacitor to smooth out bumps

bull but not so much as to smooth out audio bumps

B

D

radio signal

amplifierspeaker

Spring 2006

UCSD Physics 8 2006

19

Converting back to sound FMConverting back to sound FM

bull More sophisticatedMore sophisticatedndash need to compare instantaneous frequency to that of a

reference sourcendash then produce a voltage proportional to the differencendash Compute L = [(L+R) + (L-R)]2 R = [(L+R) - (L-R)]2ndash amplify the L and R voltages to send to speakers

bull Amplification is common to both schemesAmplification is common to both schemesndash intrinsic signal is far too weak to drive speaker

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments

Spring 2006

UCSD Physics 8 2006

12

AM RadioAM Radiobull Amplitude Modulation (AM) uses changes in the Amplitude Modulation (AM) uses changes in the

signal signal strengthstrength to convey information to convey information

pressure modulation (sound)

electromagnetic wave modulation

Spring 2006

UCSD Physics 8 2006

13

AM Radio in PracticeAM Radio in Practice

bull Uses frequency range from 530 kHz to 1700 kHzUses frequency range from 530 kHz to 1700 kHzndash each station uses 9 kHzndash spacing is 10 kHz (a little breathing room) 117 channelsndash 9 kHz of bandwidth means 45 kHz is highest audio

frequency that can be encodedbull falls short of 20 kHz capability of human ear

bull Previous diagram is exaggeratedPrevious diagram is exaggeratedndash audio signal changes slowly with respect to radio carrier

bull typical speech sound of 500 Hz varies 1000 times slower than carrier

bull thus will see 1000 cycles of carrier to every one cycle of audio

Spring 2006

UCSD Physics 8 2006

14

FM RadioFM Radiobull Frequency Modulation (FM) uses changes in the Frequency Modulation (FM) uses changes in the

waversquos waversquos frequencyfrequency to convey information to convey information

pressure modulation (sound)

electromagnetic wavemodulation

Spring 2006

UCSD Physics 8 2006

15

FM Radio in PracticeFM Radio in Practicebull Spans 878 MHz to 1080 MHz in 200 kHz intervalsSpans 878 MHz to 1080 MHz in 200 kHz intervals

ndash 101 possible stationsndash example 91X runs from 910ndash912 MHz (centered at 911)

bull Nominally uses 150 kHz around centerNominally uses 150 kHz around centerndash 75 kHz on each sidendash 30 kHz for L + R (mono) 15 kHz audio capabilityndash 30 kHz offset for stereo difference signal (L - R)

bull Again figure exaggeratedAgain figure exaggeratedndash 75 kHz from band center modulation is gt 1000 times slower

than carrier so many cycles go by before frequency noticeably changes

Spring 2006

UCSD Physics 8 2006

16

AM vs FMAM vs FM

bull FM is not inherently higher frequency than AMFM is not inherently higher frequency than AMndash these are just choicesndash aviation band is 108ndash136 MHz uses AM technique

bull Besides the greater bandwidth (leading to stereo and Besides the greater bandwidth (leading to stereo and higher audio frequencies) FM is superior in immunity higher audio frequencies) FM is superior in immunity to environmental influencesto environmental influencesndash there are lots of ways to mess with an EM-waversquos amplitude

bull pass under a bridge

bull re-orient the antenna

ndash no natural processes mess with the frequencybull FM still works in the face of amplitude foolery

Spring 2006

UCSD Physics 8 2006

17

Frequency AllocationFrequency Allocation

Spring 2006

UCSD Physics 8 2006

18

Converting back to sound AMConverting back to sound AM

bull AM is easy just pass the AC signal from the antenna AM is easy just pass the AC signal from the antenna into a diodeinto a diodendash or better yet a diode bridgendash then use capacitor to smooth out bumps

bull but not so much as to smooth out audio bumps

B

D

radio signal

amplifierspeaker

Spring 2006

UCSD Physics 8 2006

19

Converting back to sound FMConverting back to sound FM

bull More sophisticatedMore sophisticatedndash need to compare instantaneous frequency to that of a

reference sourcendash then produce a voltage proportional to the differencendash Compute L = [(L+R) + (L-R)]2 R = [(L+R) - (L-R)]2ndash amplify the L and R voltages to send to speakers

bull Amplification is common to both schemesAmplification is common to both schemesndash intrinsic signal is far too weak to drive speaker

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments

Spring 2006

UCSD Physics 8 2006

13

AM Radio in PracticeAM Radio in Practice

bull Uses frequency range from 530 kHz to 1700 kHzUses frequency range from 530 kHz to 1700 kHzndash each station uses 9 kHzndash spacing is 10 kHz (a little breathing room) 117 channelsndash 9 kHz of bandwidth means 45 kHz is highest audio

frequency that can be encodedbull falls short of 20 kHz capability of human ear

bull Previous diagram is exaggeratedPrevious diagram is exaggeratedndash audio signal changes slowly with respect to radio carrier

bull typical speech sound of 500 Hz varies 1000 times slower than carrier

bull thus will see 1000 cycles of carrier to every one cycle of audio

Spring 2006

UCSD Physics 8 2006

14

FM RadioFM Radiobull Frequency Modulation (FM) uses changes in the Frequency Modulation (FM) uses changes in the

waversquos waversquos frequencyfrequency to convey information to convey information

pressure modulation (sound)

electromagnetic wavemodulation

Spring 2006

UCSD Physics 8 2006

15

FM Radio in PracticeFM Radio in Practicebull Spans 878 MHz to 1080 MHz in 200 kHz intervalsSpans 878 MHz to 1080 MHz in 200 kHz intervals

ndash 101 possible stationsndash example 91X runs from 910ndash912 MHz (centered at 911)

bull Nominally uses 150 kHz around centerNominally uses 150 kHz around centerndash 75 kHz on each sidendash 30 kHz for L + R (mono) 15 kHz audio capabilityndash 30 kHz offset for stereo difference signal (L - R)

bull Again figure exaggeratedAgain figure exaggeratedndash 75 kHz from band center modulation is gt 1000 times slower

than carrier so many cycles go by before frequency noticeably changes

Spring 2006

UCSD Physics 8 2006

16

AM vs FMAM vs FM

bull FM is not inherently higher frequency than AMFM is not inherently higher frequency than AMndash these are just choicesndash aviation band is 108ndash136 MHz uses AM technique

bull Besides the greater bandwidth (leading to stereo and Besides the greater bandwidth (leading to stereo and higher audio frequencies) FM is superior in immunity higher audio frequencies) FM is superior in immunity to environmental influencesto environmental influencesndash there are lots of ways to mess with an EM-waversquos amplitude

bull pass under a bridge

bull re-orient the antenna

ndash no natural processes mess with the frequencybull FM still works in the face of amplitude foolery

Spring 2006

UCSD Physics 8 2006

17

Frequency AllocationFrequency Allocation

Spring 2006

UCSD Physics 8 2006

18

Converting back to sound AMConverting back to sound AM

bull AM is easy just pass the AC signal from the antenna AM is easy just pass the AC signal from the antenna into a diodeinto a diodendash or better yet a diode bridgendash then use capacitor to smooth out bumps

bull but not so much as to smooth out audio bumps

B

D

radio signal

amplifierspeaker

Spring 2006

UCSD Physics 8 2006

19

Converting back to sound FMConverting back to sound FM

bull More sophisticatedMore sophisticatedndash need to compare instantaneous frequency to that of a

reference sourcendash then produce a voltage proportional to the differencendash Compute L = [(L+R) + (L-R)]2 R = [(L+R) - (L-R)]2ndash amplify the L and R voltages to send to speakers

bull Amplification is common to both schemesAmplification is common to both schemesndash intrinsic signal is far too weak to drive speaker

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments

Spring 2006

UCSD Physics 8 2006

14

FM RadioFM Radiobull Frequency Modulation (FM) uses changes in the Frequency Modulation (FM) uses changes in the

waversquos waversquos frequencyfrequency to convey information to convey information

pressure modulation (sound)

electromagnetic wavemodulation

Spring 2006

UCSD Physics 8 2006

15

FM Radio in PracticeFM Radio in Practicebull Spans 878 MHz to 1080 MHz in 200 kHz intervalsSpans 878 MHz to 1080 MHz in 200 kHz intervals

ndash 101 possible stationsndash example 91X runs from 910ndash912 MHz (centered at 911)

bull Nominally uses 150 kHz around centerNominally uses 150 kHz around centerndash 75 kHz on each sidendash 30 kHz for L + R (mono) 15 kHz audio capabilityndash 30 kHz offset for stereo difference signal (L - R)

bull Again figure exaggeratedAgain figure exaggeratedndash 75 kHz from band center modulation is gt 1000 times slower

than carrier so many cycles go by before frequency noticeably changes

Spring 2006

UCSD Physics 8 2006

16

AM vs FMAM vs FM

bull FM is not inherently higher frequency than AMFM is not inherently higher frequency than AMndash these are just choicesndash aviation band is 108ndash136 MHz uses AM technique

bull Besides the greater bandwidth (leading to stereo and Besides the greater bandwidth (leading to stereo and higher audio frequencies) FM is superior in immunity higher audio frequencies) FM is superior in immunity to environmental influencesto environmental influencesndash there are lots of ways to mess with an EM-waversquos amplitude

bull pass under a bridge

bull re-orient the antenna

ndash no natural processes mess with the frequencybull FM still works in the face of amplitude foolery

Spring 2006

UCSD Physics 8 2006

17

Frequency AllocationFrequency Allocation

Spring 2006

UCSD Physics 8 2006

18

Converting back to sound AMConverting back to sound AM

bull AM is easy just pass the AC signal from the antenna AM is easy just pass the AC signal from the antenna into a diodeinto a diodendash or better yet a diode bridgendash then use capacitor to smooth out bumps

bull but not so much as to smooth out audio bumps

B

D

radio signal

amplifierspeaker

Spring 2006

UCSD Physics 8 2006

19

Converting back to sound FMConverting back to sound FM

bull More sophisticatedMore sophisticatedndash need to compare instantaneous frequency to that of a

reference sourcendash then produce a voltage proportional to the differencendash Compute L = [(L+R) + (L-R)]2 R = [(L+R) - (L-R)]2ndash amplify the L and R voltages to send to speakers

bull Amplification is common to both schemesAmplification is common to both schemesndash intrinsic signal is far too weak to drive speaker

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments

Spring 2006

UCSD Physics 8 2006

15

FM Radio in PracticeFM Radio in Practicebull Spans 878 MHz to 1080 MHz in 200 kHz intervalsSpans 878 MHz to 1080 MHz in 200 kHz intervals

ndash 101 possible stationsndash example 91X runs from 910ndash912 MHz (centered at 911)

bull Nominally uses 150 kHz around centerNominally uses 150 kHz around centerndash 75 kHz on each sidendash 30 kHz for L + R (mono) 15 kHz audio capabilityndash 30 kHz offset for stereo difference signal (L - R)

bull Again figure exaggeratedAgain figure exaggeratedndash 75 kHz from band center modulation is gt 1000 times slower

than carrier so many cycles go by before frequency noticeably changes

Spring 2006

UCSD Physics 8 2006

16

AM vs FMAM vs FM

bull FM is not inherently higher frequency than AMFM is not inherently higher frequency than AMndash these are just choicesndash aviation band is 108ndash136 MHz uses AM technique

bull Besides the greater bandwidth (leading to stereo and Besides the greater bandwidth (leading to stereo and higher audio frequencies) FM is superior in immunity higher audio frequencies) FM is superior in immunity to environmental influencesto environmental influencesndash there are lots of ways to mess with an EM-waversquos amplitude

bull pass under a bridge

bull re-orient the antenna

ndash no natural processes mess with the frequencybull FM still works in the face of amplitude foolery

Spring 2006

UCSD Physics 8 2006

17

Frequency AllocationFrequency Allocation

Spring 2006

UCSD Physics 8 2006

18

Converting back to sound AMConverting back to sound AM

bull AM is easy just pass the AC signal from the antenna AM is easy just pass the AC signal from the antenna into a diodeinto a diodendash or better yet a diode bridgendash then use capacitor to smooth out bumps

bull but not so much as to smooth out audio bumps

B

D

radio signal

amplifierspeaker

Spring 2006

UCSD Physics 8 2006

19

Converting back to sound FMConverting back to sound FM

bull More sophisticatedMore sophisticatedndash need to compare instantaneous frequency to that of a

reference sourcendash then produce a voltage proportional to the differencendash Compute L = [(L+R) + (L-R)]2 R = [(L+R) - (L-R)]2ndash amplify the L and R voltages to send to speakers

bull Amplification is common to both schemesAmplification is common to both schemesndash intrinsic signal is far too weak to drive speaker

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments

Spring 2006

UCSD Physics 8 2006

16

AM vs FMAM vs FM

bull FM is not inherently higher frequency than AMFM is not inherently higher frequency than AMndash these are just choicesndash aviation band is 108ndash136 MHz uses AM technique

bull Besides the greater bandwidth (leading to stereo and Besides the greater bandwidth (leading to stereo and higher audio frequencies) FM is superior in immunity higher audio frequencies) FM is superior in immunity to environmental influencesto environmental influencesndash there are lots of ways to mess with an EM-waversquos amplitude

bull pass under a bridge

bull re-orient the antenna

ndash no natural processes mess with the frequencybull FM still works in the face of amplitude foolery

Spring 2006

UCSD Physics 8 2006

17

Frequency AllocationFrequency Allocation

Spring 2006

UCSD Physics 8 2006

18

Converting back to sound AMConverting back to sound AM

bull AM is easy just pass the AC signal from the antenna AM is easy just pass the AC signal from the antenna into a diodeinto a diodendash or better yet a diode bridgendash then use capacitor to smooth out bumps

bull but not so much as to smooth out audio bumps

B

D

radio signal

amplifierspeaker

Spring 2006

UCSD Physics 8 2006

19

Converting back to sound FMConverting back to sound FM

bull More sophisticatedMore sophisticatedndash need to compare instantaneous frequency to that of a

reference sourcendash then produce a voltage proportional to the differencendash Compute L = [(L+R) + (L-R)]2 R = [(L+R) - (L-R)]2ndash amplify the L and R voltages to send to speakers

bull Amplification is common to both schemesAmplification is common to both schemesndash intrinsic signal is far too weak to drive speaker

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments

Spring 2006

UCSD Physics 8 2006

17

Frequency AllocationFrequency Allocation

Spring 2006

UCSD Physics 8 2006

18

Converting back to sound AMConverting back to sound AM

bull AM is easy just pass the AC signal from the antenna AM is easy just pass the AC signal from the antenna into a diodeinto a diodendash or better yet a diode bridgendash then use capacitor to smooth out bumps

bull but not so much as to smooth out audio bumps

B

D

radio signal

amplifierspeaker

Spring 2006

UCSD Physics 8 2006

19

Converting back to sound FMConverting back to sound FM

bull More sophisticatedMore sophisticatedndash need to compare instantaneous frequency to that of a

reference sourcendash then produce a voltage proportional to the differencendash Compute L = [(L+R) + (L-R)]2 R = [(L+R) - (L-R)]2ndash amplify the L and R voltages to send to speakers

bull Amplification is common to both schemesAmplification is common to both schemesndash intrinsic signal is far too weak to drive speaker

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments

Spring 2006

UCSD Physics 8 2006

18

Converting back to sound AMConverting back to sound AM

bull AM is easy just pass the AC signal from the antenna AM is easy just pass the AC signal from the antenna into a diodeinto a diodendash or better yet a diode bridgendash then use capacitor to smooth out bumps

bull but not so much as to smooth out audio bumps

B

D

radio signal

amplifierspeaker

Spring 2006

UCSD Physics 8 2006

19

Converting back to sound FMConverting back to sound FM

bull More sophisticatedMore sophisticatedndash need to compare instantaneous frequency to that of a

reference sourcendash then produce a voltage proportional to the differencendash Compute L = [(L+R) + (L-R)]2 R = [(L+R) - (L-R)]2ndash amplify the L and R voltages to send to speakers

bull Amplification is common to both schemesAmplification is common to both schemesndash intrinsic signal is far too weak to drive speaker

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments

Spring 2006

UCSD Physics 8 2006

19

Converting back to sound FMConverting back to sound FM

bull More sophisticatedMore sophisticatedndash need to compare instantaneous frequency to that of a

reference sourcendash then produce a voltage proportional to the differencendash Compute L = [(L+R) + (L-R)]2 R = [(L+R) - (L-R)]2ndash amplify the L and R voltages to send to speakers

bull Amplification is common to both schemesAmplification is common to both schemesndash intrinsic signal is far too weak to drive speaker

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments

Spring 2006

UCSD Physics 8 2006

20

AssignmentsAssignments

bull HW5 12E24 13E13 13E15 13E16 13P7 HW5 12E24 13E13 13E15 13E16 13P7 13P9 13P11 13P9 13P11 plus additional requiredplus additional required problems problems available on websiteavailable on website

• Radio Waves
• Electromagnetism
• Electromagnetic Radiation
• Examples of Electromagnetic Radiation
• Wavelength (Frequency)
• The Electromagnetic Spectrum
• Generation of Radio Waves
• Slide 8
• Polarization of Radio Waves
• Reception of Radio Waves
• Encoding Information on Radio Waves
• AM Radio
• AM Radio in Practice
• FM Radio
• FM Radio in Practice
• AM vs FM
• Frequency Allocation
• Converting back to sound AM
• Converting back to sound FM
• Assignments