1. Principles & Applications
Electronics
Principles & Applications
Eighth Edition
Charles A. Schuler
Chapter 12
Communications
(student version)
©2013

2. INTRODUCTION Modulation and Demodulation Simple Receivers
Superheterodyne Receivers
Frequency Modulation
Single Sideband
Wireless Data
Troubleshooting

3. 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. 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.

5. Oscillator A high-frequency oscillator can launch a radio wave.
High frequencies are often called radio frequencies.
Learning Outcome 1: Define modulation and demodulation. Page
Oscillator
The process of adding information to
the radio signal is called modulation.

6. Amplitude Modulation Modulator Radio Frequency (RF) AM = RF x AF + RF
Learning Outcome 1: Define modulation and demodulation. Page Also, Learning Outcome 2: Describe AM, FM and SSB.
Audio Frequency (AF)

7. On a spectrum analyzer, AM looks like this:
Since the RF carrier frequency is much
higher than the modulating frequency,
an actual oscilloscope display
of AM looks like this:
Learning Outcome 1: Define modulation and demodulation. Page Also, Learning Outcome 2: Describe AM, FM and SSB.
On a spectrum analyzer,
AM looks like this:

8. Oscilloscope fC = carrier frequency Spectrum Analyzer
amplitude
time
fC = carrier frequency
amplitude
frequency
Spectrum Analyzer
Learning Outcome 1: Define modulation and demodulation. Page Also, Learning Outcome 4: Predict the bandwidth of AM.
LSB = fC - fAUDIO
USB = fC + fAUDIO
AM produces sum and difference frequencies called sidebands.

9. An amplitude modulatorAF
+VCC 2p LC 1
fC = L C RF
Learning Outcome 1: Define modulation and demodulation. Page Also, Learning Outcome 2: Describe AM, FM and SSB.
(fC)
An amplitude modulator

10. The process of placing information on a carrier wave is _________.
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
Learning Outcome 1: Define modulation and demodulation. Page Also, Learning Outcome 2: Describe AM, FM and SSB.
The spectrum analyzer displays a graph of
_________ versus time.
frequency
A spectrum analyzer display of AM shows
a carrier plus two ________.
sidebands

11. 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

12. 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. An AM detector AM in Diode Audio out This capacitor approaches a short
Learning Outcome 1: Define modulation and demodulation. Page 372
This capacitor
approaches a short
circuit at the
carrier frequency.
An AM detector

14. A very basic AM receiver
Antenna
A very basic
AM receiver
Learning Outcome 3: Explain receiver operation. Page
Transmitter
Diode
Headphones

15. A practical receiver needs tuned amplifiers
to provide selectivity and sensitivity.
Learning Outcome 3: Explain receiver operation. Page
gain
frequency

16. It’s too difficult to simultaneously tune
several circuits. The IF amplifier is
permanently tuned to one frequency.
Antenna
Audio
Mixer
IF amplifier
Detector
The desired station frequency
is mixed to the IF frequency.
Oscillator
Carrier and
sidebands
IF passband
Learning Outcome 5: Calculate the oscillator frequency for superheterodyne receivers. Page

17. Frequency mixing is also called converting
or heterodyning. Receivers like this are
known as superheterodyne types.
Antenna
Mixer
IF amplifier
Detector
Learning Outcome 5: Calculate the oscillator frequency for superheterodyne receivers. Page
This is called the local oscillator
and it is tuned above the
station frequency by an amount
equal to the IF frequency.
Oscillator

18. Some typical frequencies:
fSTATION = kHz
Some typical frequencies:
fIF = 455 kHz
Mixer
IF amplifier
Detector
Learning Outcome 5: Calculate the oscillator frequency for superheterodyne receivers. Page
Oscillator
fLO = kHz
Note: the two inputs to the mixer have a difference of 455 kHz.

19. Superheterodyne receivers can also respond to the image frequency.
fSTATION = kHz
fIMAGE = kHz
( = 455)
A tuned circuit before the mixer is required.
fIF = 455 kHz
Mixer
IF amplifier
Detector
Learning Outcome 6: Calculate the image frequency for superheterodyne receivers. Page
Oscillator
fLO = kHz

20. 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. 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. 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. Frequency Modulation One way to accomplish this is to use a
varicap diode in the oscillator tank circuit. RF
Oscillator
Learning Outcome 2: List the characteristics of FM and SSB. Page
The audio signal changes the
varicap bias and the resonant
frequency of the tank circuit.
Audio Frequency (AF)

24. On a spectrum analyzer, FM shows more sidebands than AM.
Lower
sidebands
Upper
sidebands
Learning Outcome 2: List the characteristics of FM and SSB. Page fC
FM usually requires more bandwidth than AM.

25. An FM receiver can use an amplitude limiter
Noise is always a problem in any communication system. FM
has an advantage over AM since it offers better noise rejection.
FM signal
plus noise
Noise
removed
LIMITER
Modulation
preserved
Learning Outcome 2: List the characteristics of FM and SSB. Page
An FM receiver can use an amplitude limiter
to remove noise. An AM receiver cannot
since the modulation would be defeated.

26. DSBSC Modulation Balanced modulator Radio Frequency (RF)
DSBSC = RF x AF
Balanced
modulator
Learning Outcome 2: List the characteristics of FM and SSB. Page
Audio Frequency (AF)

27. DSBSC Modulation Balanced modulator LSB No carrier USB
Radio Frequency (RF)
DSBSC Modulation
Spectrum analyzer
Balanced
modulator
Learning Outcome 2: List the characteristics of FM and SSB. Page
LSB
No carrier
USB
Audio Frequency (AF)

28. Since the sidebands are redundant, one
can be filtered out to decrease bandwidth.
Balanced
modulator
Bandpass
filter
SSBSC
The lower
sideband
is not in the
passband.
Only the
upper
sideband is
transmitted.
Learning Outcome 2: List the characteristics of FM and SSB. Page
frequency

29. A superheterodyne SSB receiver requires a
second oscillator to replace the missing carrier.
Mixer
IF amplifier
Detector
Oscillator
Oscillator
Learning Outcome 2: List the characteristics of FM and SSB. Page

30. With FM, amplitude noise can be removed with a ___________. limiter
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
Learning Outcome 2: List the characteristics of FM and SSB. Page
In SSB, one of the sidebands can be eliminated
by using a ____________.
filter
SSB demodulation requires an oscillator to
replace the missing _________.
carrier

31. 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. 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.
Learning Outcome 7: Describe wireless data systems. Page 388 – 393.

33. 3 Direct-sequence spread spectrum 4 Frequency-hopping spread spectrum
Learning Outcome 7: Describe wireless data systems. Page 388 – 393.
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 1999.
3 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. Bluetooth (IEEE 802.15) 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
802.11b and g)
Learning Outcome 7: Describe wireless data systems. Page 388 – 393.
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. Radio Frequency Identification Devices (RFID) extend barcode technology into many new application areas.
Learning Outcome 7: Describe wireless data systems. Page 388 – 393.

36. Inductive Reader and Tag
Learning Outcome 7: Describe wireless data systems. Page 388 – 393.

37. Backscatter Reader and Tag
Learning Outcome 7: Describe wireless data systems. Page 388 – 393.

38. 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.
Learning Outcome 8: Troubleshoot receivers. Page 394 – 395.

39. Wireless troubleshooting
Software problems include:
Adapters are disabled
Adapters are not authenticated
Adapters are not configured properly
Learning Outcome 9: Troubleshoot wireless data systems. Page 395 – 398.

40. Wireless network troubleshooting
Hardware problems include:
Adapters are physically turned off or missing
Interference
Distance and obstructions to the signal
Multipath signal distortion
Learning Outcome 9: Troubleshoot wireless data systems. Page 395 – 398.

41. 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.
Learning Outcome 9: Troubleshoot wireless data systems. Page 395 – 398.

42. 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.
Learning Outcome 9: Troubleshoot wireless data systems. Page 395 – 398.

43. REVIEW Modulation and Demodulation Simple Receivers
Superheterodyne Receivers
Frequency Modulation
Single Sideband
Wireless Data
Troubleshooting