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12-1 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Electronics Principles & Applications Eighth Edition Chapter 12 Communications.

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Presentation on theme: "12-1 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Electronics Principles & Applications Eighth Edition Chapter 12 Communications."— Presentation transcript:

1 12-1 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Electronics Principles & Applications Eighth Edition Chapter 12 Communications (student version) Charles A. Schuler ©2013

2 12-2 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Modulation and Demodulation Simple Receivers Superheterodyne Receivers Frequency Modulation Single Sideband Wireless Data Troubleshooting INTRODUCTION

3 12-3 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Dear Student: This presentation is arranged in segments. Each segment is preceded by a Concept Preview slide and is followed by a Concept Review slide. When you reach a Concept Review slide, you can return to the beginning of that segment by clicking on the Repeat Segment button. This will allow you to view that segment again, if you want to.

4 12-4 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 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 signals carrier and sidebands.

5 12-5 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 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.

6 12-6 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Audio Frequency (AF) Radio Frequency (RF) AM = RF x AF + RF Amplitude Modulation Modulator

7 12-7 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Since the RF carrier frequency is much higher than the modulating frequency, an actual oscilloscope display of AM looks like this: On a spectrum analyzer, AM looks like this:

8 12-8 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. time amplitude Oscilloscope amplitude frequency Spectrum Analyzer f C = carrier frequency LSB = f C - f AUDIO USB = f C + f AUDIO AM produces sum and difference frequencies called sidebands.

9 12-9 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. +V CC L C 2 LC 1 f C = AF RF (f C ) An amplitude modulator

10 12-10 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. AM quiz The process of placing information on a carrier wave is _________. modulation With AM, the _________ of the carrier wave is 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 shows a carrier plus two ________. sidebands

11 12-11 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 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 signals carrier and sidebands. Repeat Segment

12 12-12 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 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.

13 12-13 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. An AM detector This capacitor approaches a short circuit at the carrier frequency. AM in Audio out Diode

14 12-14 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Transmitter Diode Antenna Headphones A very basic AM receiver

15 12-15 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. A practical receiver needs tuned amplifiers to provide selectivity and sensitivity. gain frequency

16 12-16 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. IF amplifier Oscillator Mixer Antenna Detector Its too difficult to simultaneously tune several circuits. The IF amplifier is permanently tuned to one frequency. IF passband Carrier and sidebands The desired station frequency is mixed to the IF frequency. Audio

17 12-17 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Frequency mixing is also called converting or heterodyning. Receivers like this are known as superheterodyne types. IF amplifier Oscillator Mixer Antenna Detector This is called the local oscillator and it is tuned above the station frequency by an amount equal to the IF frequency.

18 12-18 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. IF amplifier Oscillator Mixer Detector f STATION = 1020 kHz f LO = 1475 kHz f IF = 455 kHz Some typical frequencies: Note: the two inputs to the mixer have a difference of 455 kHz.

19 12-19 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. A tuned circuit before the mixer is required. IF amplifier Oscillator Mixer Detector f STATION = 1020 kHz f LO = 1475 kHz f IF = 455 kHz Superheterodyne receivers can also respond to the image frequency. f IMAGE = 1930 kHz ( = 455)

20 12-20 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Receiver quiz Recovering the information from a modulated signal is called __________. detection AM detection is often accomplished with a _________ rectifier. diode Radio receivers employ tuned amplifiers to provide sensitivity and ______. selectivity Superheterodyne receivers convert each signal to an _______ frequency. intermediate A superhet can respond to one additional frequency called the _______. image

21 12-21 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 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

22 12-22 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 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.

23 12-23 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Audio Frequency (AF) Frequency Modulation RF Oscillator One way to accomplish this is to use a varicap diode in the oscillator tank circuit. The audio signal changes the varicap bias and the resonant frequency of the tank circuit.

24 12-24 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. On a spectrum analyzer, FM shows more sidebands than AM. fCfC Upper sidebands Lower sidebands FM usually requires more bandwidth than AM.

25 12-25 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Noise is always a problem in any communication system. FM has an advantage over AM since it offers better noise rejection. LIMITER FM signal plus noise Noise removed An FM receiver can use an amplitude limiter to remove noise. An AM receiver cannot since the modulation would be defeated. Modulation preserved

26 12-26 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Audio Frequency (AF) Radio Frequency (RF) DSBSC = RF x AF DSBSC Modulation Balanced modulator

27 12-27 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Audio Frequency (AF) Radio Frequency (RF) Spectrum analyzer DSBSC Modulation Balanced modulator LSB USB No carrier

28 12-28 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. frequency Balanced modulator Bandpass filter The lower sideband is not in the passband. Since the sidebands are redundant, one can be filtered out to decrease bandwidth. SSBSC Only the upper sideband is transmitted.

29 12-29 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. IF amplifier Mixer Oscillator Detector Oscillator A superheterodyne SSB receiver requires a second oscillator to replace the missing carrier.

30 12-30 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. FM and SSB quiz With FM, amplitude noise can be removed with a ___________. limiter FM needs more bandwidth than AM since there are more _________. sidebands A balanced modulator produces sidebands but no ___________. carrier In SSB, one of the sidebands can be eliminated by using a ____________. filter SSB demodulation requires an oscillator to replace the missing _________. carrier

31 12-31 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 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

32 12-32 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 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.

33 12-33 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 1 Multiple input and multiple output antennas at both transmitter and receiver (smart antenna technology) 2 The original specification was released as IEEE in 1997 followed by a and b in Direct-sequence spread spectrum 4 Frequency-hopping spread spectrum 5 Orthogonal frequency-division multiplexing 6 IEEE y is licensed by the FCC in the United States.

34 12-34 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Bluetooth (IEEE ) Range: 10 to 100 meters Power: 1 to 100 mW Sensitivity: 0.1 nW (-70 dBm) Data rate: 1 Mbps Bluetooth II: 3 Mbps Frequency: 2.4 GHz (same as b and g) 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.

35 12-35 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Radio Frequency Identification Devices (RFID) extend barcode technology into many new application areas.

36 12-36 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Inductive Reader and Tag

37 12-37 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Backscatter Reader and Tag

38 12-38 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 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.

39 12-39 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Wireless troubleshooting Software problems include: Adapters are disabled Adapters are not authenticated Adapters are not configured properly

40 12-40 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. Wireless network troubleshooting Hardware problems include: Adapters are physically turned off or missing Interference Distance and obstructions to the signal Multipath signal distortion

41 12-41 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 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.

42 12-42 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 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.

43 12-43 McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. REVIEW Modulation and Demodulation Simple Receivers Superheterodyne Receivers Frequency Modulation Single Sideband Wireless Data Troubleshooting


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