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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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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