2. McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Electronics Principles & Applications Seventh Edition Chapter 12 Communications (student version) Charles A. Schuler McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved.

3. McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Modulation and Demodulation Simple Receivers Superheterodyne Receivers Frequency Modulation Single Sideband Receiver Troubleshooting INTRODUCTION

4. McGraw-Hill © 2008 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.

5. McGraw-Hill © 2008 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 signal’s carrier and sidebands.

6. McGraw-Hill © 2008 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.

7. McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Audio Frequency (AF) Radio Frequency (RF) AM = RF x AF + RF Amplitude Modulation Modulator

8. McGraw-Hill © 2008 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:

9. McGraw-Hill © 2008 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.

10. McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. +V CC L C 22 LC 1 f C = AF RF (f C ) An amplitude modulator

11. McGraw-Hill © 2008 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

12. McGraw-Hill © 2008 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 signal’s carrier and sidebands. Repeat Segment

13. McGraw-Hill © 2008 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.

14. McGraw-Hill © 2008 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

15. McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Transmitter Diode Antenna Headphones A very basic AM receiver

16. McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. A practical receiver needs tuned amplifiers to provide selectivity and sensitivity. gain frequency

17. McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. IF amplifier Oscillator Mixer Antenna Detector It’s 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

18. McGraw-Hill © 2008 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.

19. McGraw-Hill © 2008 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.

20. McGraw-Hill © 2008 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 (1930 - 1475 = 455)

21. McGraw-Hill © 2008 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

22. McGraw-Hill © 2008 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

23. McGraw-Hill © 2008 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.

24. McGraw-Hill © 2008 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.

25. McGraw-Hill © 2008 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.

26. McGraw-Hill © 2008 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

27. McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Audio Frequency (AF) Radio Frequency (RF) DSBSC = RF x AF DSBSC Modulation Balanced modulator

28. McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Audio Frequency (AF) Radio Frequency (RF) Spectrum analyzer DSBSC Modulation Balanced modulator LSB USB No carrier

29. McGraw-Hill © 2008 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.

30. McGraw-Hill © 2008 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.

31. McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Bluetooth Range: 10 to 100 meters Power: 1 to 100 mW Sensitivity: 0.1 nW (-70 dBm) Frequency: 2.4 GHz Data rate: 1 Mbit/s

32. McGraw-Hill © 2008 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.

33. McGraw-Hill © 2008 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

34. McGraw-Hill © 2008 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

35. McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. REVIEW Modulation and Demodulation Simple Receivers Superheterodyne Receivers Frequency Modulation Single Sideband Receiver Troubleshooting