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![Page 1: 12-1 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Electronics Principles & Applications Eighth Edition Chapter 12 Communications.](https://reader033.fdocuments.us/reader033/viewer/2022061306/5514735f5503462d4e8b617c/html5/thumbnails/1.jpg)
12-1
McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved.
ElectronicsElectronics
Principles & ApplicationsPrinciples & ApplicationsEighth EditionEighth Edition
Chapter 12Communications(student version)
Charles A. Schuler
©2013
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• Modulation and Demodulation• Simple Receivers• Superheterodyne Receivers• Frequency Modulation• Single Sideband• Wireless Data• Troubleshooting
INTRODUCTION
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Dear Student:
This presentation is arranged in segments. Each segmentis preceded by a Concept Preview slide and is followed by aConcept Review slide. When you reach a Concept Reviewslide, you can return to the beginning of that segment byclicking on the Repeat Segment button. This will allow youto view that segment again, if you want to.
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Concept Preview• Modulation is the process of adding information to
an RF signal.• The information signal controls the amplitude of
the RF signal when amplitude modulation is used.• The envelope of an AM signal has the same shape
as the information signal (oscilloscope display).• AM produces upper and lower sidebands.• A spectrum analyzer displays an AM signal’s
carrier and sidebands.
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Oscillator
A high-frequency oscillator can launch a radio wave.
The process of adding information to the radio signal is called modulation.
High frequencies are often called radio frequencies.
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Audio Frequency (AF)
Radio Frequency (RF)
AM = RF x AF + RF
Amplitude Modulation
Modulator
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Since the RF carrier frequency is muchhigher than the modulating frequency,
an actual oscilloscope displayof AM looks like this:
On a spectrum analyzer,AM looks like this:
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time
amp
litu
de
Oscilloscope
amp
litu
de
frequency
Spectrum Analyzer
fC = carrier frequency
LSB = fC - fAUDIO
USB = fC + fAUDIO
AM produces sum and difference frequencies called sidebands.
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+VCC
L C
2 LC
1fC =
AF
RF
(fC)
An amplitude modulator
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AM quiz
The process of placing information on acarrier wave is _________. modulation
With AM, the _________ of the carrier waveis controlled or varied. amplitude
The oscilloscope displays a graph of ________versus time. amplitude
The spectrum analyzer displays a graph of_________ versus time. frequency
A spectrum analyzer display of AM showsa carrier plus two ________. sidebands
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Concept Review• Modulation is the process of adding information to
an RF signal.• The information signal controls the amplitude of
the RF signal when amplitude modulation is used.• The envelope of an AM signal has the same shape
as the information signal (oscilloscope display).• AM produces upper and lower sidebands.• A spectrum analyzer displays an AM signal’s
carrier and sidebands.
Repeat Segment
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Concept Preview• Information signal recovery is called detection.
AM receivers often use a diode detector.• Tuned amplifiers provide selectivity so that only
the desired station will be received.• Superheterodyne receivers use an intermediate
frequency (IF) before detection.• A local oscillator is mixed with the desired station
to convert it to the intermediate frequency.• An image frequency will also mix with the
oscillator and produce the intermediate frequency.• Selectivity before the mixer eliminates the image.
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An AM detector
This capacitorapproaches a short
circuit at the carrier frequency.
AM in Audio outDiode
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Transmitter Diode
Antenna
Headphones
A very basic AM receiver
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A practical receiver needs tuned amplifiersto provide selectivity and sensitivity.
gain
frequency
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IF amplifier
Oscillator
Mixer
Antenna
Detector
It’s too difficult to simultaneously tuneseveral circuits. The IF amplifier is
permanently tuned to one frequency.
IF passbandCarrier andsidebands
The desired station frequency is mixed to the IF frequency.
Audio
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Frequency mixing is also called convertingor heterodyning. Receivers like this are
known as superheterodyne types.
IF amplifier
Oscillator
Mixer
Antenna
Detector
This is called the local oscillatorand it is tuned above the
station frequency by an amountequal to the IF frequency.
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IF amplifier
Oscillator
Mixer Detector
fSTATION = 1020 kHz
fLO = 1475 kHz
fIF = 455 kHz
Some typical frequencies:
Note: the two inputs to the mixer have a difference of 455 kHz.
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A tuned circuit before the mixer is required.
IF amplifier
Oscillator
Mixer Detector
fSTATION = 1020 kHz
fLO = 1475 kHz
fIF = 455 kHz
Superheterodyne receivers can also respond to the image frequency.
fIMAGE = 1930 kHz
(1930 - 1475 = 455)
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Receiver quiz
Recovering the information from a modulatedsignal is called __________. detection
AM detection is often accomplished with a_________ rectifier. diode
Radio receivers employ tuned amplifiers toprovide sensitivity and ______. selectivity
Superheterodyne receivers convert eachsignal to an _______ frequency. intermediate
A superhet can respond to one additionalfrequency called the _______. image
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Concept Review• Information signal recovery is called detection.
AM receivers often use a diode detector.• Tuned amplifiers provide selectivity so that only
the desired station will be received.• Superheterodyne receivers use an intermediate
frequency (IF) before detection.• A local oscillator is mixed with the desired station
to convert it to the intermediate frequency.• An image frequency will also mix with the
oscillator and produce the intermediate frequency.• Selectivity before the mixer eliminates the image.
Repeat Segment
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Concept Preview• With frequency modulation (FM), the information
signal controls the frequency of the carrier.• FM produces more sidebands than AM and thus
has greater bandwidth.• Noise and static can be removed from an FM
signal by clipping.• The carrier in an AM signal can be eliminated by
using a balanced modulator.• Single sideband AM also eliminates one of the
sidebands.
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Audio Frequency (AF)
Frequency Modulation
RFOscillator
One way to accomplish this is to use a varicap diode in the oscillator tank circuit.
The audio signal changes thevaricap bias and the resonantfrequency of the tank circuit.
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On a spectrum analyzer, FM shows more sidebands than AM.
fC
Uppersidebands
Lowersidebands
FM usually requires more bandwidth than AM.
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Noise is always a problem in any communication system. FM has an advantage over AM since it offers better noise rejection.
LIMITER
FM signalplus noise
Noiseremoved
An FM receiver can use an amplitude limiter to remove noise. An AM receiver cannot since the modulation would be defeated.
Modulationpreserved
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Audio Frequency (AF)
Radio Frequency (RF)
DSBSC = RF x AF
DSBSC Modulation
Balancedmodulator
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Audio Frequency (AF)
Radio Frequency (RF)
Spectrum analyzer
DSBSC Modulation
Balancedmodulator
LSB USBNo carrier
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frequency
Balancedmodulator
Bandpassfilter
The lowersideband
is not in thepassband.
Since the sidebands are redundant, one can be filtered out to decrease bandwidth.
SSBSC
Only theupper
sideband istransmitted.
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IF amplifierMixer
Oscillator
Detector
Oscillator
A superheterodyne SSB receiver requires a second oscillator to replace the missing carrier.
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FM and SSB quiz
With FM, amplitude noise can be removedwith a ___________. limiter
FM needs more bandwidth than AM sincethere are more _________. sidebands
A balanced modulator produces sidebandsbut no ___________. carrier
In SSB, one of the sidebands can be eliminatedby using a ____________. filter
SSB demodulation requires an oscillator toreplace the missing _________. carrier
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Concept Review• With frequency modulation (FM), the information
signal controls the frequency of the carrier.• FM produces more sidebands than AM and thus
has greater bandwidth.• Noise and static can be removed from an FM
signal by clipping.• The carrier in an AM signal can be eliminated by
using a balanced modulator.• Single sideband AM also eliminates one of the
sidebands.
Repeat Segment
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Wireless data devices are providing faster and more convenient communication and operation in several key areas. Here, the discussion is limited to WiFi, Bluetooth, and RFID technology.
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1 Multiple input and multiple output antennas at both transmitter and receiver (smart antenna technology)2 The original specification was released as IEEE 802.11 in 1997 followed by 802.11a and 802.11b in 1999.3 Direct-sequence spread spectrum4 Frequency-hopping spread spectrum5 Orthogonal frequency-division multiplexing6 IEEE 802.11y is licensed by the FCC in the United States.
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Bluetooth (IEEE 802.15)Range: 10 to 100 metersPower: 1 to 100 mWSensitivity: 0.1 nW (-70 dBm)Data rate: 1 MbpsBluetooth II: 3 MbpsFrequency: 2.4 GHz (same as 802.11b and 802.11g)
Bluetooth technology is designed for personal area networks (PANs) and for appliances that don't require large data flows (printers, keyboards, mice, personal computers, and mobile phones). Bluetooth enable automobiles allow hands-free phone operation.
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Radio Frequency Identification Devices (RFID) extend barcode technology into many new application areas.
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Inductive Reader and Tag
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Backscatter Reader and Tag
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Receiver troubleshooting
• Signal injection is standard practice.
• Both AF and RF signal generators may be required.
• Some receivers may require adjustments of their tuned circuits. This is called alignment.
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Wireless troubleshooting
Software problems include:
• Adapters are disabled
• Adapters are not authenticated
• Adapters are not configured properly
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Wireless network troubleshooting
Hardware problems include:
• Adapters are physically turned off or missing
• Interference
• Distance and obstructions to the signal
• Multipath signal distortion
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A field-strength meter can be used to determine if transmitters are working at all. However, this type of go/no-go test will only identify a limited range of possible problems.
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More advanced wireless network troubleshooting can be accomplished with dedicated test equipment or with special software running on general purpose equipment such as notebook computers and some portable devices.
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REVIEW
• Modulation and Demodulation• Simple Receivers• Superheterodyne Receivers• Frequency Modulation• Single Sideband• Wireless Data• Troubleshooting